• MySQL 5.1 Reference Manual :: 17 MySQL Cluster NDB 6.X/7.X :: 17.3 MySQL Cluster Configuration :: 17.3.2 MySQL Cluster Configuration Files :: 17.3.2.6 Defining MySQL Cluster Data Nodes
  • 17.3.2.6. Defining MySQL Cluster Data Nodes

    The [ndbd] and [ndbd default] sections are used to configure the behavior of the cluster's data nodes.

    [ndbd] and [ndbd default] are always used as the section names whether you are using ndbd or (in MySQL Cluster NDB 6.4.0 and later) ndbmtd binaries for the data node processes.

    There are many parameters which control buffer sizes, pool sizes, timeouts, and so forth. The only mandatory parameters are:

    • Either ExecuteOnComputer or HostName, which must be defined in the local [ndbd] section.

    • The parameter NoOfReplicas, which must be defined in the[ndbd default]section, as it is common to all Cluster data nodes.

    Note

    It is no longer strictly necessary to set NoOfReplicas starting with MySQL Cluster NDB 6.3.25 and MySQL Cluster NDB 7.0.6, where it acquires a default value (2). However, it remains good practice to set it explicitly.

    Most data node parameters are set in the [ndbd default] section. Only those parameters explicitly stated as being able to set local values are allowed to be changed in the [ndbd] section. Where present, HostName, Id and ExecuteOnComputer must be defined in the local [ndbd] section, and not in any other section of config.ini. In other words, settings for these parameters are specific to one data node.

    For those parameters affecting memory usage or buffer sizes, it is possible to use K, M, or G as a suffix to indicate units of 1024, 1024×1024, or 1024×1024×1024. (For example, 100K means 100 × 1024 = 102400.) Parameter names and values are currently case-sensitive.

    Information about configuration parameters specific to MySQL Cluster Disk Data tables can be found later in this section.

    Beginning with MySQL Cluster NDB 6.4.0, all of these parameters also apply to ndbmtd (the multi-threaded version of ndbd). An additional data node configuration parameter MaxNoOfExecutionThreads applies to ndbmtd only, and has no effect when used with ndbd. For more information, see Section 17.4.3, “ndbmtd — The MySQL Cluster Data Node Daemon (Multi-Threaded)”.

    Identifying data nodes.  The Id value (that is, the data node identifier) can be allocated on the command line when the node is started or in the configuration file.

    • Id

      Restart Type node
        Permitted Values
      Type numeric
      Default
      Range 1-48

      This is the node ID used as the address of the node for all cluster internal messages. For data nodes, this is an integer in the range 1 to 48 inclusive. Each node in the cluster must have a unique identifier.

      This parameter can also be written as NodeId, although the short form is sufficient (and preferred for this reason).

    • ExecuteOnComputer

      Restart Type system
        Permitted Values
      Type string
      Default
      Range -

      This refers to the Id set for one of the computers defined in a [computer] section.

    • HostName

      Restart Type system
        Permitted Values
      Type string
      Default localhost
      Range -

      Specifying this parameter defines the hostname of the computer on which the data node is to reside. To specify a hostname other than localhost, either this parameter or ExecuteOnComputer is required.

    • ServerPort

      Restart Type node
        Permitted Values
      Type numeric
      Default
      Range 1-64K

      Each node in the cluster uses a port to connect to other nodes. By default, this port is allocated dynamically in such a way as to ensure that no two nodes on the same host computer receive the same port number, so it should normally not be necessary to specify a value for this parameter.

      However, if you need to be able to open specific ports in a firewall to permit communication between data nodes and API nodes (including SQL nodes), you can set this parameter to the number of the desired port in an [ndbd] section or (if you need to do this for multiple data nodes) the [ndbd default] section of the config.ini file, and then open the port having that number for incoming connections from SQL nodes, API nodes, or both.

      Note

      Connections from data nodes to management nodes is done via the ndb_mgmd management port (the management server's PortNumber; see Section 17.3.2.5, “Defining a MySQL Cluster Management Server”) so outgoing connections to that port from any data nodes should always be allowed.

    • TcpBind_INADDR_ANY

      Setting this parameter to TRUE or 1 binds IP_ADDR_ANY so that connections can be made from anywhere (for autogenerated connections). The default is FALSE (0).

      This parameter was added in MySQL Cluster NDB 6.2.0.

    • NodeGroup

      Version Introduced 5.1.30-ndb-6.4.0
      Restart Type initial, system
        Permitted Values
      Type numeric
      Default
      Range 0-64K

      This parameter can be used to assign a data node to a specific node group. It is read only when the cluster is started for the first time, and cannot be used to reassign a data node to a different node group online. It is generally not desirable to use this parameter in the [ndbd default] section of the config.ini file, and care must be taken not to assign nodes to node groups in such a way that an invalid numbers of nodes are assigned to any node groups.

      The NodeGroup parameter is chiefly intended for use in adding a new node group to a running MySQL Cluster without having to perform a rolling restart. For this purpose, you should set it to 65535 (the maximum value). You are not required to set a NodeGroup value for all cluster data nodes, only for those nodes which are to be started and added to the cluster as a new node group at a later time. For more information, see Section 17.5.11.3, “Adding MySQL Cluster Data Nodes Online: Detailed Example”.

      This parameter was added in MySQL Cluster NDB 6.4.0.

    • NoOfReplicas

      Restart Type initial, system
        Permitted Values
      Type numeric
      Default None
      Range 1-4
        Permitted Values
      Type numeric
      Default None
      Range 1-4
        Permitted Values
      Type numeric
      Default 2
      Range 1-4
        Permitted Values
      Type numeric
      Default 2
      Range 1-4

      This global parameter can be set only in the [ndbd default] section, and defines the number of replicas for each table stored in the cluster. This parameter also specifies the size of node groups. A node group is a set of nodes all storing the same information.

      Node groups are formed implicitly. The first node group is formed by the set of data nodes with the lowest node IDs, the next node group by the set of the next lowest node identities, and so on. By way of example, assume that we have 4 data nodes and that NoOfReplicas is set to 2. The four data nodes have node IDs 2, 3, 4 and 5. Then the first node group is formed from nodes 2 and 3, and the second node group by nodes 4 and 5. It is important to configure the cluster in such a manner that nodes in the same node groups are not placed on the same computer because a single hardware failure would cause the entire cluster to fail.

      If no node IDs are provided, the order of the data nodes will be the determining factor for the node group. Whether or not explicit assignments are made, they can be viewed in the output of the management client's SHOW command.

      Prior to MySQL Cluster NDB 6.3.25 and MySQL Cluster NDB 7.0.6, there was no default value for NoOfReplicas; beginning with these versions, the default value is 2, which is the recommended setting in most common usage scenarios. (Bug#44746)

      The maximum possible value is 4; currently, only the values 1 and 2 are actually supported (see Bug#18621).

      Important

      Setting NoOfReplicas to 1 means that there is only a single copy of all Cluster data; in this case, the loss of a single data node causes the cluster to fail because there are no additional copies of the data stored by that node.

      The value for this parameter must divide evenly into the number of data nodes in the cluster. For example, if there are two data nodes, then NoOfReplicas must be equal to either 1 or 2, since 2/3 and 2/4 both yield fractional values; if there are four data nodes, then NoOfReplicas must be equal to 1, 2, or 4.

    • DataDir

      Restart Type initial, node
        Permitted Values
      Type string
      Default .
      Range -

      This parameter specifies the directory where trace files, log files, pid files and error logs are placed.

      The default is the data node process working directory.

    • FileSystemPath

      Version Introduced 5.1.15-ndb-6.1.1
      Restart Type initial, node
        Permitted Values
      Type string
      Default DataDir
      Range -

      This parameter specifies the directory where all files created for metadata, REDO logs, UNDO logs (for Disk Data tables), and data files are placed. The default is the directory specified by DataDir.

      Note

      This directory must exist before the ndbd process is initiated.

      The recommended directory hierarchy for MySQL Cluster includes /var/lib/mysql-cluster, under which a directory for the node's file system is created. The name of this subdirectory contains the node ID. For example, if the node ID is 2, this subdirectory is named ndb_2_fs.

    • BackupDataDir

      Restart Type initial, node
        Permitted Values
      Type string
      Default FileSystemPath
      Range -

      This parameter specifies the directory in which backups are placed.

      Important

      The string '/BACKUP' is always appended to this value. For example, if you set the value of BackupDataDir to /var/lib/cluster-data, then all backups are stored under /var/lib/cluster-data/BACKUP. This also means that the effective default backup location is the directory named BACKUP under the location specified by the FileSystemPath parameter.

    Data Memory, Index Memory, and String Memory

    DataMemory and IndexMemory are [ndbd] parameters specifying the size of memory segments used to store the actual records and their indexes. In setting values for these, it is important to understand how DataMemory and IndexMemory are used, as they usually need to be updated to reflect actual usage by the cluster:

    • DataMemory

      Restart Type node
        Permitted Values
      Type numeric
      Default 80M
      Range 1M-1024G

      This parameter defines the amount of space (in bytes) available for storing database records. The entire amount specified by this value is allocated in memory, so it is extremely important that the machine has sufficient physical memory to accommodate it.

      The memory allocated by DataMemory is used to store both the actual records and indexes. There is a 16-byte overhead on each record; an additional amount for each record is incurred because it is stored in a 32KB page with 128 byte page overhead (see below). There is also a small amount wasted per page due to the fact that each record is stored in only one page.

      For variable-size table attributes in MySQL 5.1, the data is stored on separate datapages, allocated from DataMemory. Variable-length records use a fixed-size part with an extra overhead of 4 bytes to reference the variable-size part. The variable-size part has 2 bytes overhead plus 2 bytes per attribute.

      The maximum record size is currently 8052 bytes.

      The memory space defined by DataMemory is also used to store ordered indexes, which use about 10 bytes per record. Each table row is represented in the ordered index. A common error among users is to assume that all indexes are stored in the memory allocated by IndexMemory, but this is not the case: Only primary key and unique hash indexes use this memory; ordered indexes use the memory allocated by DataMemory. However, creating a primary key or unique hash index also creates an ordered index on the same keys, unless you specify USING HASH in the index creation statement. This can be verified by running ndb_desc -d db_name table_name in the management client.

      The memory space allocated by DataMemory consists of 32KB pages, which are allocated to table fragments. Each table is normally partitioned into the same number of fragments as there are data nodes in the cluster. Thus, for each node, there are the same number of fragments as are set in NoOfReplicas.

      In addition, due to the way in which new pages are allocated when the capacity of the current page is exhausted, there is an additional overhead of approximately 18.75%. When more DataMemory is required, more than one new page is allocated, according to the following formula:

      number of new pages = FLOOR(number of current pages × 0.1875) + 1
      

      For example, if 15 pages are currently allocated to a given table and an insert to this table requires additional storage space, the number of new pages allocated to the table is FLOOR(15 × 0.1875) + 1 = FLOOR(2.8125) + 1 = 2 + 1 = 3. Now 15 + 3 = 18 memory pages are allocated to the table. When the last of these 18 pages becomes full, FLOOR(18 × 0.1875) + 1 = FLOOR(3.3750) + 1 = 3 + 1 = 4 new pages are allocated, so the total number of pages allocated to the table is now 22.

      Note

      The “18.75% + 1” overhead is no longer required beginning with MySQL Cluster NDB 6.2.3 and MySQL Cluster NDB 6.3.0.

      Once a page has been allocated, it is currently not possible to return it to the pool of free pages, except by deleting the table. (This also means that DataMemory pages, once allocated to a given table, cannot be used by other tables.) Performing a node recovery also compresses the partition because all records are inserted into empty partitions from other live nodes.

      The DataMemory memory space also contains UNDO information: For each update, a copy of the unaltered record is allocated in the DataMemory. There is also a reference to each copy in the ordered table indexes. Unique hash indexes are updated only when the unique index columns are updated, in which case a new entry in the index table is inserted and the old entry is deleted upon commit. For this reason, it is also necessary to allocate enough memory to handle the largest transactions performed by applications using the cluster. In any case, performing a few large transactions holds no advantage over using many smaller ones, for the following reasons:

      • Large transactions are not any faster than smaller ones

      • Large transactions increase the number of operations that are lost and must be repeated in event of transaction failure

      • Large transactions use more memory

      The default value for DataMemory is 80MB; the minimum is 1MB. There is no maximum size, but in reality the maximum size has to be adapted so that the process does not start swapping when the limit is reached. This limit is determined by the amount of physical RAM available on the machine and by the amount of memory that the operating system may commit to any one process. 32-bit operating systems are generally limited to 2–4GB per process; 64-bit operating systems can use more. For large databases, it may be preferable to use a 64-bit operating system for this reason.

    • IndexMemory

      Restart Type node
        Permitted Values
      Type numeric
      Default 18M
      Range 1M-1T

      This parameter controls the amount of storage used for hash indexes in MySQL Cluster. Hash indexes are always used for primary key indexes, unique indexes, and unique constraints. Note that when defining a primary key and a unique index, two indexes will be created, one of which is a hash index used for all tuple accesses as well as lock handling. It is also used to enforce unique constraints.

      The size of the hash index is 25 bytes per record, plus the size of the primary key. For primary keys larger than 32 bytes another 8 bytes is added.

      The default value for IndexMemory is 18MB. The minimum is 1MB.

    • StringMemory

      Restart Type system
        Permitted Values (>= 5.1.6)
      Type numeric
      Default 5
      Range 0-4G

      This parameter determines how much memory is allocated for strings such as table names, and is specified in an [ndbd] or [ndbd default] section of the config.ini file. A value between 0 and 100 inclusive is interpreted as a percent of the maximum default value, which is calculated based on a number of factors including the number of tables, maximum table name size, maximum size of .FRM files, MaxNoOfTriggers, maximum column name size, and maximum default column value. In general it is safe to assume that the maximum default value is approximately 5 MB for a MySQL Cluster having 1000 tables.

      A value greater than 100 is interpreted as a number of bytes.

      Beginning with MySQL Cluster NDB 6.2.18, MySQL Cluster NDB 6.3.24, and MySQL Cluster NDB 7.0.5, the default value is 25—that is, 25 percent of the default maximum, or approximately 25 KB. (Previously, the default value was 5 beginning with MySQL 5.1.6; prior to MySQL 5.1.6, the default was 0.)

      Under most circumstances, the default value should be sufficient, but when you have a great many Cluster tables (1000 or more), it is possible to get Error 773 Out of string memory, please modify StringMemory config parameter: Permanent error: Schema error, in which case you should increase this value. 25 (25 percent) is not excessive, and should prevent this error from recurring in all but the most extreme conditions.

    The following example illustrates how memory is used for a table. Consider this table definition:

    CREATE TABLE example (
      a INT NOT NULL,
      b INT NOT NULL,
      c INT NOT NULL,
      PRIMARY KEY(a),
      UNIQUE(b)
    ) ENGINE=NDBCLUSTER;
    

    For each record, there are 12 bytes of data plus 12 bytes overhead. Having no nullable columns saves 4 bytes of overhead. In addition, we have two ordered indexes on columns a and b consuming roughly 10 bytes each per record. There is a primary key hash index on the base table using roughly 29 bytes per record. The unique constraint is implemented by a separate table with b as primary key and a as a column. This other table consumes an additional 29 bytes of index memory per record in the example table as well 8 bytes of record data plus 12 bytes of overhead.

    Thus, for one million records, we need 58MB for index memory to handle the hash indexes for the primary key and the unique constraint. We also need 64MB for the records of the base table and the unique index table, plus the two ordered index tables.

    You can see that hash indexes takes up a fair amount of memory space; however, they provide very fast access to the data in return. They are also used in MySQL Cluster to handle uniqueness constraints.

    Currently, the only partitioning algorithm is hashing and ordered indexes are local to each node. Thus, ordered indexes cannot be used to handle uniqueness constraints in the general case.

    An important point for both IndexMemory and DataMemory is that the total database size is the sum of all data memory and all index memory for each node group. Each node group is used to store replicated information, so if there are four nodes with two replicas, there will be two node groups. Thus, the total data memory available is 2 × DataMemory for each data node.

    It is highly recommended that DataMemory and IndexMemory be set to the same values for all nodes. Data distribution is even over all nodes in the cluster, so the maximum amount of space available for any node can be no greater than that of the smallest node in the cluster.

    DataMemory and IndexMemory can be changed, but decreasing either of these can be risky; doing so can easily lead to a node or even an entire MySQL Cluster that is unable to restart due to there being insufficient memory space. Increasing these values should be acceptable, but it is recommended that such upgrades are performed in the same manner as a software upgrade, beginning with an update of the configuration file, and then restarting the management server followed by restarting each data node in turn.

    Updates do not increase the amount of index memory used. Inserts take effect immediately; however, rows are not actually deleted until the transaction is committed.

    Transaction parameters.  The next three [ndbd] parameters that we discuss are important because they affect the number of parallel transactions and the sizes of transactions that can be handled by the system. MaxNoOfConcurrentTransactions sets the number of parallel transactions possible in a node. MaxNoOfConcurrentOperations sets the number of records that can be in update phase or locked simultaneously.

    Both of these parameters (especially MaxNoOfConcurrentOperations) are likely targets for users setting specific values and not using the default value. The default value is set for systems using small transactions, to ensure that these do not use excessive memory.

    • MaxNoOfConcurrentTransactions

      Restart Type system
        Permitted Values
      Type numeric
      Default 4096
      Range 32-4G

      Each cluster data node requires a transaction record for each active transaction in the cluster. The task of coordinating transactions is distributed among all of the data nodes. The total number of transaction records in the cluster is the number of transactions in any given node times the number of nodes in the cluster.

      Transaction records are allocated to individual MySQL servers. Each connection to a MySQL server requires at least one transaction record, plus an additional transaction object per table accessed by that connection. This means that a reasonable minimum for this parameter is

      MaxNoOfConcurrentTransactions =
          (maximum number of tables accessed in any single transaction + 1)
          * number of cluster SQL nodes
      

      Suppose that there are 4 SQL nodes using the cluster. A single join involving 5 tables requires 6 transaction records; if there are 5 such joins in a transaction, then 5 * 6 = 30 transaction records are required for this transaction, per MySQL server, or 30 * 4 = 120 transaction records total.

      This parameter must be set to the same value for all cluster data nodes. This is due to the fact that, when a data node fails, the oldest surviving node re-creates the transaction state of all transactions that were ongoing in the failed node.

      Changing the value of MaxNoOfConcurrentTransactions requires a complete shutdown and restart of the cluster.

      The default value is 4096.

    • MaxNoOfConcurrentOperations

      Restart Type node
        Permitted Values
      Type numeric
      Default 32K
      Range 32-4G

      It is a good idea to adjust the value of this parameter according to the size and number of transactions. When performing transactions of only a few operations each and not involving a great many records, there is no need to set this parameter very high. When performing large transactions involving many records need to set this parameter higher.

      Records are kept for each transaction updating cluster data, both in the transaction coordinator and in the nodes where the actual updates are performed. These records contain state information needed to find UNDO records for rollback, lock queues, and other purposes.

      This parameter should be set to the number of records to be updated simultaneously in transactions, divided by the number of cluster data nodes. For example, in a cluster which has four data nodes and which is expected to handle 1,000,000 concurrent updates using transactions, you should set this value to 1000000 / 4 = 250000.

      Read queries which set locks also cause operation records to be created. Some extra space is allocated within individual nodes to accommodate cases where the distribution is not perfect over the nodes.

      When queries make use of the unique hash index, there are actually two operation records used per record in the transaction. The first record represents the read in the index table and the second handles the operation on the base table.

      The default value is 32768.

      This parameter actually handles two values that can be configured separately. The first of these specifies how many operation records are to be placed with the transaction coordinator. The second part specifies how many operation records are to be local to the database.

      A very large transaction performed on an eight-node cluster requires as many operation records in the transaction coordinator as there are reads, updates, and deletes involved in the transaction. However, the operation records of the are spread over all eight nodes. Thus, if it is necessary to configure the system for one very large transaction, it is a good idea to configure the two parts separately. MaxNoOfConcurrentOperations will always be used to calculate the number of operation records in the transaction coordinator portion of the node.

      It is also important to have an idea of the memory requirements for operation records. These consume about 1KB per record.

    • MaxNoOfLocalOperations

      Restart Type node
        Permitted Values
      Type numeric
      Default UNDEFINED
      Range 32-4G

      By default, this parameter is calculated as 1.1 × MaxNoOfConcurrentOperations. This fits systems with many simultaneous transactions, none of them being very large. If there is a need to handle one very large transaction at a time and there are many nodes, it is a good idea to override the default value by explicitly specifying this parameter.

    Transaction temporary storage.  The next set of [ndbd] parameters is used to determine temporary storage when executing a statement that is part of a Cluster transaction. All records are released when the statement is completed and the cluster is waiting for the commit or rollback.

    The default values for these parameters are adequate for most situations. However, users with a need to support transactions involving large numbers of rows or operations may need to increase these values to enable better parallelism in the system, whereas users whose applications require relatively small transactions can decrease the values to save memory.

    • MaxNoOfConcurrentIndexOperations

      Restart Type node
        Permitted Values
      Type numeric
      Default 8K
      Range 0-4G

      For queries using a unique hash index, another temporary set of operation records is used during a query's execution phase. This parameter sets the size of that pool of records. Thus, this record is allocated only while executing a part of a query. As soon as this part has been executed, the record is released. The state needed to handle aborts and commits is handled by the normal operation records, where the pool size is set by the parameter MaxNoOfConcurrentOperations.

      The default value of this parameter is 8192. Only in rare cases of extremely high parallelism using unique hash indexes should it be necessary to increase this value. Using a smaller value is possible and can save memory if the DBA is certain that a high degree of parallelism is not required for the cluster.

    • MaxNoOfFiredTriggers

      Restart Type node
        Permitted Values
      Type numeric
      Default 4000
      Range 0-4G

      The default value of MaxNoOfFiredTriggers is 4000, which is sufficient for most situations. In some cases it can even be decreased if the DBA feels certain the need for parallelism in the cluster is not high.

      A record is created when an operation is performed that affects a unique hash index. Inserting or deleting a record in a table with unique hash indexes or updating a column that is part of a unique hash index fires an insert or a delete in the index table. The resulting record is used to represent this index table operation while waiting for the original operation that fired it to complete. This operation is short-lived but can still require a large number of records in its pool for situations with many parallel write operations on a base table containing a set of unique hash indexes.

    • TransactionBufferMemory

      Restart Type node
        Permitted Values
      Type numeric
      Default 1M
      Range 1K-4G

      The memory affected by this parameter is used for tracking operations fired when updating index tables and reading unique indexes. This memory is used to store the key and column information for these operations. It is only very rarely that the value for this parameter needs to be altered from the default.

      The default value for TransactionBufferMemory is 1MB.

      Normal read and write operations use a similar buffer, whose usage is even more short-lived. The compile-time parameter ZATTRBUF_FILESIZE (found in ndb/src/kernel/blocks/Dbtc/Dbtc.hpp) set to 4000 × 128 bytes (500KB). A similar buffer for key information, ZDATABUF_FILESIZE (also in Dbtc.hpp) contains 4000 × 16 = 62.5KB of buffer space. Dbtc is the module that handles transaction coordination.

    Scans and buffering.  There are additional [ndbd] parameters in the Dblqh module (in ndb/src/kernel/blocks/Dblqh/Dblqh.hpp) that affect reads and updates. These include ZATTRINBUF_FILESIZE, set by default to 10000 × 128 bytes (1250KB) and ZDATABUF_FILE_SIZE, set by default to 10000*16 bytes (roughly 156KB) of buffer space. To date, there have been neither any reports from users nor any results from our own extensive tests suggesting that either of these compile-time limits should be increased.

    • MaxNoOfConcurrentScans

      Restart Type node
        Permitted Values
      Type numeric
      Default 256
      Range 2-500

      This parameter is used to control the number of parallel scans that can be performed in the cluster. Each transaction coordinator can handle the number of parallel scans defined for this parameter. Each scan query is performed by scanning all partitions in parallel. Each partition scan uses a scan record in the node where the partition is located, the number of records being the value of this parameter times the number of nodes. The cluster should be able to sustain MaxNoOfConcurrentScans scans concurrently from all nodes in the cluster.

      Scans are actually performed in two cases. The first of these cases occurs when no hash or ordered indexes exists to handle the query, in which case the query is executed by performing a full table scan. The second case is encountered when there is no hash index to support the query but there is an ordered index. Using the ordered index means executing a parallel range scan. The order is kept on the local partitions only, so it is necessary to perform the index scan on all partitions.

      The default value of MaxNoOfConcurrentScans is 256. The maximum value is 500.

    • MaxNoOfLocalScans

      Restart Type node
        Permitted Values
      Type numeric
      Default UNDEFINED
      Range 32-4G

      Specifies the number of local scan records if many scans are not fully parallelized. If the number of local scan records is not provided, it is calculated as the product of MaxNoOfConcurrentScans and the number of data nodes in the system. The minimum value is 32.

    • BatchSizePerLocalScan

      Restart Type node
        Permitted Values
      Type numeric
      Default 64
      Range 1-992

      This parameter is used to calculate the number of lock records used to handle concurrent scan operations.

      The default value is 64; this value has a strong connection to the ScanBatchSize defined in the SQL nodes.

    • LongMessageBuffer

      Restart Type node
        Permitted Values
      Type numeric
      Default 1M
      Range 512K-4G
        Permitted Values
      Type numeric
      Default 4M
      Range 512K-4G

      This is an internal buffer used for passing messages within individual nodes and between nodes. In MySQL Cluster NDB 6.4.3 and earlier, the default is 1MB; beginning with MySQL Cluster NDB 7.0.4, it is 4MB.

      This parameter seldom needs to be changed from the default. However, when replicating a MySQL Cluster using ndbmtd for the data nodes, you may need to increase this value to 8MB (or possibly more) to prevent data node instability, because ndbmtd uses much more of this resource than ndbd does. Beginning with MySQL Cluster NDB 7.0.13 and MySQL Cluster NDB 7.1.2, this should no longer be necessary when using ndbmtd with MySQL Cluster Replication (Bug#46914).

    Memory Allocation

    MaxAllocate

    This is the maximum size of the memory unit to use when allocating memory for tables. In cases where NDB gives Out of memory errors, but it is evident by examining the cluster logs or the output of DUMP 1000 (see DUMP 1000) that all available memory has not yet been used, you can increase the value of this parameter (or MaxNoOfTables, or both) in order to cause NDB to make sufficient memory available.

    This parameter was introduced in MySQL 5.1.20, MySQL Cluster NDB 6.1.12 and MySQL Cluster NDB 6.2.3.

    Logging and checkpointing

    The following [ndbd] parameters control log and checkpoint behavior.

    • NoOfFragmentLogFiles

      Restart Type initial, node
        Permitted Values (>= 5.1.0)
      Type numeric
      Default 16
      Range 3-4G

      This parameter sets the number of REDO log files for the node, and thus the amount of space allocated to REDO logging. Because the REDO log files are organized in a ring, it is extremely important that the first and last log files in the set (sometimes referred to as the “head” and “tail” log files, respectively) do not meet. When these approach one another too closely, the node begins aborting all transactions encompassing updates due to a lack of room for new log records.

      A REDO log record is not removed until the required number of local checkpoints has been completed since that log record was inserted (prior to MySQL Cluster NDB 6.3.8, this was 3 local checkpoints; in later versions of MySQL Cluster, only 2 local checkpoints are necessary). Checkpointing frequency is determined by its own set of configuration parameters discussed elsewhere in this chapter.

      How these parameters interact and proposals for how to configure them are discussed in Section 17.3.2.12, “Configuring MySQL Cluster Parameters for Local Checkpoints”.

      The default parameter value is 16, which by default means 16 sets of 4 16MB files for a total of 1024MB. Beginning with MySQL Cluster NDB 6.1.1, the size of the individual log files is configurable using the FragmentLogFileSize parameter; more information about this parameter can be found here. In scenarios requiring a great many updates, the value for NoOfFragmentLogFiles may need to be set as high as 300 or even higher to provide sufficient space for REDO logs.

      If the checkpointing is slow and there are so many writes to the database that the log files are full and the log tail cannot be cut without jeopardizing recovery, all updating transactions are aborted with internal error code 410 (Out of log file space temporarily). This condition prevails until a checkpoint has completed and the log tail can be moved forward.

      Important

      This parameter cannot be changed “on the fly”; you must restart the node using --initial. If you wish to change this value for all data nodes in a running cluster, you can do so via a rolling node restart (using --initial when starting each data node).

    • FragmentLogFileSize

      Version Introduced 5.1.15-ndb-6.1.11
      Restart Type initial, node
        Permitted Values
      Type numeric
      Default 16M
      Range 4M-1G

      Setting this parameter allows you to control directly the size of redo log files. This can be useful in situations when MySQL Cluster is operating under a high load and it is unable to close fragment log files quickly enough before attempting to open new ones (only 2 fragment log files can be open at one time); increasing the size of the fragment log files gives the cluster more time before having to open each new fragment log file. The default value for this parameter is 16M. FragmentLogFileSize was added in MySQL Cluster NDB 6.1.11.

      For more information about fragment log files, see the description of the NoOfFragmentLogFiles parameter.

    • InitFragmentLogFiles

      Version Introduced 5.1.29-ndb-6.3.19
      Restart Type node
        Permitted Values
      Type string
      Default
      Range -

      By default, fragment log files are created sparsely when performing an initial start of a data node—that is, depending on the operating system and file system in use, not all bytes are necessarily written to disk. Beginning with MySQL Cluster NDB 6.3.19, it is possible to override this behavior and force all bytes to be written regardless of the platform and file system type being used by mean of this parameter.

      InitFragmentLogFiles takes one of two values:

      • SPARSE. Fragment log files are created sparsely. This is the default value.

      • FULL. Force all bytes of the fragment log file to be written to disk.

      Depending on your operating system and file system, setting InitFragmentLogFiles=FULL may help eliminate I/O errors on writes to the REDO log.

    • MaxNoOfOpenFiles

      Restart Type node
        Permitted Values (<= 5.1.15)
      Type numeric
      Default 40
      Range 20-4G
        Permitted Values (>= 5.1.16)
      Type numeric
      Default 0
      Range 20-4G

      This parameter sets a ceiling on how many internal threads to allocate for open files. Any situation requiring a change in this parameter should be reported as a bug.

      The default value is 0. (Prior to MySQL 5.1.16, the default was 40.) However, the minimum value to which this parameter can be set is 20.

    • InitialNoOfOpenFiles

      Version Introduced 5.1.9
      Restart Type node
        Permitted Values (>= 5.1.9)
      Type numeric
      Default 27
      Range 20-4G

      This parameter sets the initial number of internal threads to allocate for open files.

      The default value is 27.

    • MaxNoOfSavedMessages

      Restart Type node
        Permitted Values
      Type numeric
      Default 25
      Range 0-4G

      This parameter sets the maximum number of trace files that are kept before overwriting old ones. Trace files are generated when, for whatever reason, the node crashes.

      The default is 25 trace files.

    • MaxLCPStartDelay

      Version Introduced 5.1.32-ndb-6.4.3
      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-600
        Permitted Values
      Type numeric
      Default 0
      Range 0-600

      In parallel data node recovery (supported in MySQL Cluster NDB 6.3.8 and later), only table data is actually copied and synchronized in parallel; synchronization of metadata such as dictionary and checkpoint information is done in a serial fashion. In addition, recovery of dictionary and checkpoint information cannot be executed in parallel with performing of local checkpoints. This means that, when starting or restarting many data nodes concurrently, data nodes may be forced to wait while a local checkpoint is performed, which can result in longer node recovery times.

      Beginning with MySQL Cluster NDB 6.3.23 and MySQL Cluster NDB 6.4.3, it is possible to force a delay in the local checkpoint to allow more (and possibly all) data nodes to complete metadata synchronization; once each data node's metadata synchronization is complete, all of the data nodes can recover table data in parallel, even while the local checkpoint is being executed.

      To force such a delay, you can set MaxLCPStartDelay, which determines the number of seconds the cluster can wait to begin a local checkpoint while data nodes continue to synchronize metadata. This parameter should be set in the [ndbd default] section of the config.ini file, so that it is the same for all data nodes. The maximum value is 600; the default is 0.

    Metadata objects.  The next set of [ndbd] parameters defines pool sizes for metadata objects, used to define the maximum number of attributes, tables, indexes, and trigger objects used by indexes, events, and replication between clusters. Note that these act merely as “suggestions” to the cluster, and any that are not specified revert to the default values shown.

    • MaxNoOfAttributes

      Restart Type node
        Permitted Values
      Type numeric
      Default 1000
      Range 32-4G

      Defines the number of attributes that can be defined in the cluster.

      The default value is 1000, with the minimum possible value being 32. The maximum is 4294967039. Each attribute consumes around 200 bytes of storage per node due to the fact that all metadata is fully replicated on the servers.

      When setting MaxNoOfAttributes, it is important to prepare in advance for any ALTER TABLE statements that you might want to perform in the future. This is due to the fact, during the execution of ALTER TABLE on a Cluster table, 3 times the number of attributes as in the original table are used, and a good practice is to allow double this amount. For example, if the MySQL Cluster table having the greatest number of attributes (greatest_number_of_attributes) has 100 attributes, a good starting point for the value of MaxNoOfAttributes would be 6 * greatest_number_of_attributes = 600.

      You should also estimate the average number of attributes per table and multiply this by MaxNoOfTables. If this value is larger than the value obtained in the previous paragraph, you should use the larger value instead.

      Assuming that you can create all desired tables without any problems, you should also verify that this number is sufficient by trying an actual ALTER TABLE after configuring the parameter. If this is not successful, increase MaxNoOfAttributes by another multiple of MaxNoOfTables and test it again.

    • MaxNoOfTables

      Restart Type node
        Permitted Values
      Type numeric
      Default 128
      Range 8-20320

      A table object is allocated for each table and for each unique hash index in the cluster. This parameter sets the maximum number of table objects for the cluster as a whole.

      For each attribute that has a BLOB data type an extra table is used to store most of the BLOB data. These tables also must be taken into account when defining the total number of tables.

      The default value of this parameter is 128. The minimum is 8 and the maximum is 20320. Each table object consumes approximately 20KB per node.

      Note

      The sum of MaxNoOfTables, MaxNoOfOrderedIndexes, and MaxNoOfUniqueHashIndexes must not exceed 232 – 2 (4294967294).

    • MaxNoOfOrderedIndexes

      Restart Type node
        Permitted Values
      Type numeric
      Default 128
      Range 0-4G

      For each ordered index in the cluster, an object is allocated describing what is being indexed and its storage segments. By default, each index so defined also defines an ordered index. Each unique index and primary key has both an ordered index and a hash index. MaxNoOfOrderedIndexes sets the total number of hash indexes that can be in use in the system at any one time.

      The default value of this parameter is 128. Each hash index object consumes approximately 10KB of data per node.

      Note

      The sum of MaxNoOfTables, MaxNoOfOrderedIndexes, and MaxNoOfUniqueHashIndexes must not exceed 232 – 2 (4294967294).

    • MaxNoOfUniqueHashIndexes

      Restart Type node
        Permitted Values
      Type numeric
      Default 64
      Range 0-4G

      For each unique index that is not a primary key, a special table is allocated that maps the unique key to the primary key of the indexed table. By default, an ordered index is also defined for each unique index. To prevent this, you must specify the USING HASH option when defining the unique index.

      The default value is 64. Each index consumes approximately 15KB per node.

      Note

      The sum of MaxNoOfTables, MaxNoOfOrderedIndexes, and MaxNoOfUniqueHashIndexes must not exceed 232 – 2 (4294967294).

    • MaxNoOfTriggers

      Restart Type node
        Permitted Values
      Type numeric
      Default 768
      Range 0-4G

      Internal update, insert, and delete triggers are allocated for each unique hash index. (This means that three triggers are created for each unique hash index.) However, an ordered index requires only a single trigger object. Backups also use three trigger objects for each normal table in the cluster.

      Replication between clusters also makes use of internal triggers.

      This parameter sets the maximum number of trigger objects in the cluster.

      The default value is 768.

    • MaxNoOfIndexes

      This parameter is deprecated in MySQL 5.1; you should use MaxNoOfOrderedIndexes and MaxNoOfUniqueHashIndexes instead.

      This parameter is used only by unique hash indexes. There needs to be one record in this pool for each unique hash index defined in the cluster.

      The default value of this parameter is 128.

    • MaxNoOfSubscriptions

      Version Introduced 5.1.23-ndb-6.3.7
      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-4G
        Permitted Values
      Type numeric
      Default 0
      Range 0-4G

      Each NDB table in a MySQL Cluster requires a subscription in the NDB kernel. For some NDB API applications, it may be necessary or desirable to change this parameter, which became available in MySQL Cluster NDB 6.2.10 and MySQL Cluster NDB 6.3.7. However, for normal usage with MySQL servers acting as SQL nodes, there is not any need to do so.

      The default value for MaxNoOfSubscriptions is 0, which is treated as equal to MaxNoOfTables.

    • MaxNoOfSubscribers

      Version Introduced 5.1.23-ndb-6.3.7
      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-4G
        Permitted Values
      Type numeric
      Default 0
      Range 0-4G

      This parameter, added in MySQL Cluster NDB 6.2.10 and MySQL Cluster NDB 6.3.7, is of interest only when using MySQL Cluster Replication. The default value is 0, which is treated as 2 * MaxNoOfTables; that is, there is one subscription per NDB table for each of two MySQL servers (one acting as the replication master and the other as the slave).

      When using circular replication, multi-master replcation, and other replication setups involving more than 2 MySQL servers, you should increase this parameter to the number of mysqld processes included in replication (this is often, but not always, the same as the number of clusters). For example, if you have a circular replication setup using three MySQL Clusters, with one mysqld attached to each cluster, and each of these mysqld processes acts as a master and as a slave, you should set MaxNoOfSubscribers equal to 3 * MaxNoOfTables.

      For more information, see Section 17.6, “MySQL Cluster Replication”.

    • MaxNoOfConcurrentSubOperations

      Version Introduced 5.1.23-ndb-6.3.7
      Restart Type node
        Permitted Values
      Type numeric
      Default 256
      Range 0-4G
        Permitted Values
      Type numeric
      Default 256
      Range 0-4G

      This parameter sets a ceiling on the number of operations that can be performed by all API nodes in the cluster at one time. The default value (256) is sufficient for normal operations, and might need to be adjusted only in scenarios where there are a great many API nodes each performing a high volume of operations concurrently.

      This parameter was added in MySQL Cluster NDB 6.2.10 and MySQL Cluster NDB 6.3.7.

    Boolean parameters.  The behavior of data nodes is also affected by a set of [ndbd] parameters taking on boolean values. These parameters can each be specified as TRUE by setting them equal to 1 or Y, and as FALSE by setting them equal to 0 or N.

    • LockPagesInMainMemory

      Restart Type node
        Permitted Values (>= 5.1.0, <= 5.1.14)
      Type boolean
      Default 0
      Range 0-1
        Permitted Values (>= 5.1.15)
      Type numeric
      Default 0
      Range 0-2

      For a number of operating systems, including Solaris and Linux, it is possible to lock a process into memory and so avoid any swapping to disk. This can be used to help guarantee the cluster's real-time characteristics.

      Beginning with MySQL 5.1.15 and MySQL Cluster NDB 6.1.1, this parameter takes one of the integer values 0, 1, or 2, which act as follows:

      • 0: Disables locking. This is the default value.

      • 1: Performs the lock after allocating memory for the process.

      • 2: Performs the lock before memory for the process is allocated.

      Previously, this parameter was a Boolean. 0 or false was the default setting, and disabled locking. 1 or true enabled locking of the process after its memory was allocated.

      Important

      Beginning with MySQL 5.1.15 and MySQL Cluster NDB 6.1.1, it is no longer possible to use true or false for the value of this parameter; when upgrading from a previous version, you must change the value to 0, 1, or 2.

      Prior to MySQL Cluster NDB 6.3.31 and MySQL Cluster NDB 7.0.11, setting this parameter did not cause the stated memory to be allocated when the node was started, but rather only when the memory was used by the data node process for other reasons. (Bug#37430)

      Note

      If the operating system is not configured to allow unprivileged users to lock pages, then the data node process making use of this parameter may have to be run as system root. (LockPagesInMainMemory uses the mlockall function. From Linux kernel 2.6.9, unprivileged users can lock memory as limited by max locked memory. For more information, see ulimit -l and http://linux.die.net/man/2/mlock).

    • StopOnError

      Restart Type node
        Permitted Values
      Type boolean
      Default true
      Range -

      This parameter specifies whether an ndbd process should exit or perform an automatic restart when an error condition is encountered.

      This feature is enabled by default.

    • Diskless

      Restart Type initial, system
        Permitted Values
      Type boolean
      Default 0
      Range 0-1

      It is possible to specify MySQL Cluster tables as diskless, meaning that tables are not checkpointed to disk and that no logging occurs. Such tables exist only in main memory. A consequence of using diskless tables is that neither the tables nor the records in those tables survive a crash. However, when operating in diskless mode, it is possible to run ndbd on a diskless computer.

      Important

      This feature causes the entire cluster to operate in diskless mode.

      When this feature is enabled, Cluster online backup is disabled. In addition, a partial start of the cluster is not possible.

      Diskless is disabled by default.

    • ODirect

      Version Introduced 5.1.19-ndb-6.3.0
      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-1
        Permitted Values
      Type numeric
      Default 0
      Range 0-1
        Permitted Values
      Type numeric
      Default 0
      Range 0-1

      Enabling this parameter causes NDB to attempt using O_DIRECT writes for LCP, backups, and redo logs, often lowering kswapd and CPU usage. When using MySQL Cluster on Linux, enable ODirect if you are using a 2.6 or kernel.

      This parameter was added in the following releases:

      • MySQL 5.1.20

      • MySQL Cluster NDB 6.1.11

      • MySQL Cluster NDB 6.2.3

      • MySQL Cluster NDB 6.3.0

      ODirect is disabled by default.

    • RestartOnErrorInsert

      Restart Type node
        Permitted Values
      Type numeric
      Default 2
      Range 0-4

      This feature is accessible only when building the debug version where it is possible to insert errors in the execution of individual blocks of code as part of testing.

      This feature is disabled by default.

    • CompressedBackup

      Version Introduced 5.1.23-ndb-6.3.7
      Restart Type node
        Permitted Values
      Type boolean
      Default false
      Range -

      Setting this parameter to 1 causes backup files to be compressed. The compression used is equivalent to gzip --fast, and can save 50% or more of the space required on the data node to store uncompressed backup files. Compressed backups can be enabled for individual data nodes, or for all data nodes (by setting this parameter in the [ndbd default] section of the config.ini file).

      Important

      You cannot restore a compressed backup to a cluster running a MySQL version that does not support this feature.

      The default value is 0 (disabled).

      This parameter was introduced in MySQL Cluster NDB 6.3.7.

    • CompressedLCP

      Version Introduced 5.1.23-ndb-6.3.7
      Restart Type node
        Permitted Values
      Type boolean
      Default false
      Range -

      Setting this parameter to 1 causes local checkpoint files to be compressed. The compression used is equivalent to gzip --fast, and can save 50% or more of the space required on the data node to store uncompressed checkpoint files. Compressed LCPs can be enabled for individual data nodes, or for all data nodes (by setting this parameter in the [ndbd default] section of the config.ini file).

      Important

      You cannot restore a compressed local checkpoint to a cluster running a MySQL version that does not support this feature.

      The default value is 0 (disabled).

      This parameter was introduced in MySQL Cluster NDB 6.3.7.

    Controlling Timeouts, Intervals, and Disk Paging

    There are a number of [ndbd] parameters specifying timeouts and intervals between various actions in Cluster data nodes. Most of the timeout values are specified in milliseconds. Any exceptions to this are mentioned where applicable.

    • TimeBetweenWatchDogCheck

      Restart Type node
        Permitted Values
      Type numeric
      Default 6000
      Range 70-4G

      To prevent the main thread from getting stuck in an endless loop at some point, a “watchdog” thread checks the main thread. This parameter specifies the number of milliseconds between checks. If the process remains in the same state after three checks, the watchdog thread terminates it.

      This parameter can easily be changed for purposes of experimentation or to adapt to local conditions. It can be specified on a per-node basis although there seems to be little reason for doing so.

      The default timeout is 6000 milliseconds (6 seconds).

    • TimeBetweenWatchDogCheckInitial

      Version Introduced 5.1.20
      Restart Type node
        Permitted Values (>= 5.1.20)
      Type numeric
      Default 6000
      Range 70-4G

      This is similar to the TimeBetweenWatchDogCheck parameter, except that TimeBetweenWatchDogCheckInitial controls the amount of time that passes between execution checks inside a database node in the early start phases during which memory is allocated.

      The default timeout is 6000 milliseconds (6 seconds).

      This parameter was added in MySQL 5.1.20.

    • StartPartialTimeout

      Restart Type node
        Permitted Values
      Type numeric
      Default 30000
      Range 0-4G

      This parameter specifies how long the Cluster waits for all data nodes to come up before the cluster initialization routine is invoked. This timeout is used to avoid a partial Cluster startup whenever possible.

      This parameter is overridden when performing an initial start or initial restart of the cluster.

      The default value is 30000 milliseconds (30 seconds). 0 disables the timeout, in which case the cluster may start only if all nodes are available.

    • StartPartitionedTimeout

      Restart Type node
        Permitted Values
      Type numeric
      Default 60000
      Range 0-4G

      If the cluster is ready to start after waiting for StartPartialTimeout milliseconds but is still possibly in a partitioned state, the cluster waits until this timeout has also passed. If StartPartitionedTimeout is set to 0, the cluster waits indefinitely.

      This parameter is overridden when performing an initial start or initial restart of the cluster.

      The default timeout is 60000 milliseconds (60 seconds).

    • StartFailureTimeout

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-4G

      If a data node has not completed its startup sequence within the time specified by this parameter, the node startup fails. Setting this parameter to 0 (the default value) means that no data node timeout is applied.

      For nonzero values, this parameter is measured in milliseconds. For data nodes containing extremely large amounts of data, this parameter should be increased. For example, in the case of a data node containing several gigabytes of data, a period as long as 10–15 minutes (that is, 600000 to 1000000 milliseconds) might be required to perform a node restart.

    • HeartbeatIntervalDbDb

      Restart Type node
        Permitted Values
      Type numeric
      Default 1500
      Range 10-4G

      One of the primary methods of discovering failed nodes is by the use of heartbeats. This parameter states how often heartbeat signals are sent and how often to expect to receive them. After missing three heartbeat intervals in a row, the node is declared dead. Thus, the maximum time for discovering a failure through the heartbeat mechanism is four times the heartbeat interval.

      The default heartbeat interval is 1500 milliseconds (1.5 seconds). This parameter must not be changed drastically and should not vary widely between nodes. If one node uses 5000 milliseconds and the node watching it uses 1000 milliseconds, obviously the node will be declared dead very quickly. This parameter can be changed during an online software upgrade, but only in small increments.

    • HeartbeatIntervalDbApi

      Restart Type node
        Permitted Values
      Type numeric
      Default 1500
      Range 100-4G

      Each data node sends heartbeat signals to each MySQL server (SQL node) to ensure that it remains in contact. If a MySQL server fails to send a heartbeat in time it is declared “dead,” in which case all ongoing transactions are completed and all resources released. The SQL node cannot reconnect until all activities initiated by the previous MySQL instance have been completed. The three-heartbeat criteria for this determination are the same as described for HeartbeatIntervalDbDb.

      The default interval is 1500 milliseconds (1.5 seconds). This interval can vary between individual data nodes because each data node watches the MySQL servers connected to it, independently of all other data nodes.

    • TimeBetweenLocalCheckpoints

      Restart Type node
        Permitted Values
      Type numeric
      Default 20
      Range 0-31

      This parameter is an exception in that it does not specify a time to wait before starting a new local checkpoint; rather, it is used to ensure that local checkpoints are not performed in a cluster where relatively few updates are taking place. In most clusters with high update rates, it is likely that a new local checkpoint is started immediately after the previous one has been completed.

      The size of all write operations executed since the start of the previous local checkpoints is added. This parameter is also exceptional in that it is specified as the base-2 logarithm of the number of 4-byte words, so that the default value 20 means 4MB (4 × 220) of write operations, 21 would mean 8MB, and so on up to a maximum value of 31, which equates to 8GB of write operations.

      All the write operations in the cluster are added together. Setting TimeBetweenLocalCheckpoints to 6 or less means that local checkpoints will be executed continuously without pause, independent of the cluster's workload.

    • TimeBetweenGlobalCheckpoints

      Restart Type node
        Permitted Values
      Type numeric
      Default 2000
      Range 10-32000

      When a transaction is committed, it is committed in main memory in all nodes on which the data is mirrored. However, transaction log records are not flushed to disk as part of the commit. The reasoning behind this behavior is that having the transaction safely committed on at least two autonomous host machines should meet reasonable standards for durability.

      It is also important to ensure that even the worst of cases—a complete crash of the cluster—is handled properly. To guarantee that this happens, all transactions taking place within a given interval are put into a global checkpoint, which can be thought of as a set of committed transactions that has been flushed to disk. In other words, as part of the commit process, a transaction is placed in a global checkpoint group. Later, this group's log records are flushed to disk, and then the entire group of transactions is safely committed to disk on all computers in the cluster.

      This parameter defines the interval between global checkpoints. The default is 2000 milliseconds.

    • TimeBetweenEpochs

      Version Introduced 5.1.22-ndb-6.3.2
      Restart Type node
        Permitted Values
      Type numeric
      Default 100
      Range 0-32000
        Permitted Values
      Type numeric
      Default 100
      Range 0-32000

      This parameter defines the interval between synchronisation epochs for MySQL Cluster Replication. The default value is 100 milliseconds.

      TimeBetweenEpochs is part of the implementation of “micro-GCPs”, which can be used to improve the performance of MySQL Cluster Replication. This parameter was introduced in MySQL Cluster NDB 6.2.5 and MySQL Cluster NDB 6.3.2.

    • TimeBetweenEpochsTimeout

      Version Introduced 5.1.22-ndb-6.3.4
      Restart Type node
        Permitted Values
      Type numeric
      Default 4000
      Range 0-32000
        Permitted Values
      Type numeric
      Default 4000
      Range 0-32000

      This parameter defines a timeout for synchronisation epochs for MySQL Cluster Replication. If a node fails to participate in a global checkpoint within the time determined by this parameter, the node is shut down. The default value is 4000 milliseconds.

      TimeBetweenEpochsTimeout is part of the implementation of “micro-GCPs”, which can be used to improve the performance of MySQL Cluster Replication. This parameter was introduced in MySQL Cluster NDB 6.2.7 and MySQL Cluster NDB 6.3.4.

    • MaxBufferedEpochs

      Version Introduced 5.1.23-ndb-6.2.14
      Restart Type node
        Permitted Values
      Type numeric
      Default 100
      Range 0-100000

      The number of unprocessed epochs by which a subscribing node can lag behind. Exceeding this number causes a lagging subscriber to be disconnected.

      The default value of 100 is sufficient for most normal operations. If a subscribing node does lag enough to cause disconnections, it is usually due to network or scheduling issues with regard to processes or threads. (In rare circumstances, the problem may be due to a bug in the NDB client.) It may be desirable to set the value lower than the default when epochs are longer.

      Disconnection prevents client issues from affecting the data node service, running out of memory to buffer data, and eventually shutting down. Instead, only the client is affected as a result of the disconnect (by, for example gap events in the binlog), forcing the client to reconnect or restart the process.

    • TimeBetweenInactiveTransactionAbortCheck

      Restart Type node
        Permitted Values
      Type numeric
      Default 1000
      Range 1000-4G

      Timeout handling is performed by checking a timer on each transaction once for every interval specified by this parameter. Thus, if this parameter is set to 1000 milliseconds, every transaction will be checked for timing out once per second.

      The default value is 1000 milliseconds (1 second).

    • TransactionInactiveTimeout

      Restart Type node
        Permitted Values
      Type numeric
      Default 4G
      Range 0-4G

      This parameter states the maximum time that is permitted to lapse between operations in the same transaction before the transaction is aborted.

      The default for this parameter is zero (no timeout). For a real-time database that needs to ensure that no transaction keeps locks for too long, this parameter should be set to a relatively small value. The unit is milliseconds.

    • TransactionDeadlockDetectionTimeout

      Restart Type node
        Permitted Values
      Type numeric
      Default 1200
      Range 50-4G

      When a node executes a query involving a transaction, the node waits for the other nodes in the cluster to respond before continuing. A failure to respond can occur for any of the following reasons:

      • The node is “dead

      • The operation has entered a lock queue

      • The node requested to perform the action could be heavily overloaded.

      This timeout parameter states how long the transaction coordinator waits for query execution by another node before aborting the transaction, and is important for both node failure handling and deadlock detection. In MySQL 5.1.10 and earlier versions, setting it too high could cause undesirable behavior in situations involving deadlocks and node failure. Beginning with MySQL 5.1.11, active transactions occurring during node failures are actively aborted by the MySQL Cluster Transaction Coordinator, and so high settings are no longer an issue with this parameter.

      The default timeout value is 1200 milliseconds (1.2 seconds).

      Prior to MySQL Cluster NDB versions 6.2.18, 6.3.24, and 7.0.5, the effective minimum for this parameter was 100 milliseconds. (Bug#44099) Beginning with these versions, the actual minimum is 50 milliseconds.

    • DiskSyncSize

      Version Introduced 5.1.12
      Restart Type node
        Permitted Values
      Type numeric
      Default 4M
      Range 32K-4G

      This is the maximum number of bytes to store before flushing data to a local checkpoint file. This is done in order to prevent write buffering, which can impede performance significantly. This parameter is not intended to take the place of TimeBetweenLocalCheckpoints.

      Note

      When ODirect is enabled, it is not necessary to set DiskSyncSize; in fact, in such cases its value is simply ignored.

      The default value is 4M (4 megabytes).

      This parameter was added in MySQL 5.1.12.

    • DiskCheckpointSpeed

      Version Introduced 5.1.12
      Restart Type node
        Permitted Values
      Type numeric
      Default 10M
      Range 1M-4G

      The amount of data,in bytes per second, that is sent to disk during a local checkpoint. This allocation is shared by DML operations and backups (but not backup logging), which means that backups started during times of intensive DML may be impaired by flooding of the redo log buffer and may fail altogether if the contention is sufficiently severe.

      The default value is 10M (10 megabytes per second).

      This parameter was added in MySQL 5.1.12.

    • DiskCheckpointSpeedInRestart

      Version Introduced 5.1.12
      Restart Type node
        Permitted Values
      Type numeric
      Default 10M
      Range 1M-4G

      The amount of data,in bytes per second, that is sent to disk during a local checkpoint as part of a restart operation.

      The default value is 100M (100 megabytes per second).

      This parameter was added in MySQL 5.1.12.

    • NoOfDiskPagesToDiskAfterRestartTUP

      Version Removed 5.1.6
      Restart Type node
        Permitted Values (<= 5.1.6)
      Type numeric
      Default 40
      Range 1-4G

      When executing a local checkpoint, the algorithm flushes all data pages to disk. Merely doing so as quickly as possible without any moderation is likely to impose excessive loads on processors, networks, and disks. To control the write speed, this parameter specifies how many pages per 100 milliseconds are to be written. In this context, a “page” is defined as 8KB. This parameter is specified in units of 80KB per second, so setting NoOfDiskPagesToDiskAfterRestartTUP to a value of 20 entails writing 1.6MB in data pages to disk each second during a local checkpoint. This value includes the writing of UNDO log records for data pages. That is, this parameter handles the limitation of writes from data memory. (See the entry for IndexMemory for information about index pages.)

      In short, this parameter specifies how quickly to execute local checkpoints. It operates in conjunction with NoOfFragmentLogFiles, DataMemory, and IndexMemory.

      For more information about the interaction between these parameters and possible strategies for choosing appropriate values for them, see Section 17.3.2.12, “Configuring MySQL Cluster Parameters for Local Checkpoints”.

      The default value is 40 (3.2MB of data pages per second).

      Note

      This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeed and DiskSyncSize instead.

    • NoOfDiskPagesToDiskAfterRestartACC

      Version Removed 5.1.6
      Restart Type node
        Permitted Values (<= 5.1.6)
      Type numeric
      Default 20
      Range 1-4G

      This parameter uses the same units as NoOfDiskPagesToDiskAfterRestartTUP and acts in a similar fashion, but limits the speed of writing index pages from index memory.

      The default value of this parameter is 20 (1.6MB of index memory pages per second).

      Note

      This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeed and DiskSyncSize.

    • NoOfDiskPagesToDiskDuringRestartTUP

      Version Removed 5.1.6
      Restart Type node
        Permitted Values (<= 5.1.6)
      Type numeric
      Default 40
      Range 1-4G

      This parameter is used in a fashion similar to NoOfDiskPagesToDiskAfterRestartTUP and NoOfDiskPagesToDiskAfterRestartACC, only it does so with regard to local checkpoints executed in the node when a node is restarting. A local checkpoint is always performed as part of all node restarts. During a node restart it is possible to write to disk at a higher speed than at other times, because fewer activities are being performed in the node.

      This parameter covers pages written from data memory.

      The default value is 40 (3.2MB per second).

      Note

      This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeedInRestart and DiskSyncSize.

    • NoOfDiskPagesToDiskDuringRestartACC

      Version Removed 5.1.6
      Restart Type node
        Permitted Values (<= 5.1.6)
      Type numeric
      Default 20
      Range 1-4G

      Controls the number of index memory pages that can be written to disk during the local checkpoint phase of a node restart.

      As with NoOfDiskPagesToDiskAfterRestartTUP and NoOfDiskPagesToDiskAfterRestartACC, values for this parameter are expressed in terms of 8KB pages written per 100 milliseconds (80KB/second).

      The default value is 20 (1.6MB per second).

      Note

      This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeedInRestart and DiskSyncSize.

    • ArbitrationTimeout

      Restart Type node
        Permitted Values
      Type numeric
      Default 1000
      Range 10-4G

      This parameter specifies how long data nodes wait for a response from the arbitrator to an arbitration message. If this is exceeded, the network is assumed to have split.

      The default value is 1000 milliseconds (1 second).

    • Arbitration

      Version Introduced 5.1.35-ndb-7.0.7
      Restart Type node
        Permitted Values
      Type enumeration
      Default Default
      Valid Values Default, Disabled, WaitExternal

      The Arbitration parameter, added in MySQL Cluster NDB 7.0.7, allows a choice of arbitration schemes, corresponding to one of 3 possible values for this parameter:

      • Default This allows arbitration to proceed normally, as determined by the ArbitrationRank settings for the management and API nodes. This is the default value.

      • Disabled Previously, it was possible to disable arbitration only by setting ArbitrationRank to 0 on all management and API nodes. Now, you can now use Arbitration = Disabled in the [ndbd default] section of the config.ini file to accomplish this task. In this case, any ArbitrationRank settings are ignored.

      • WaitExternal The Arbitration parameter also makes it possible to configure arbitration in such a way that the cluster waits until after the time determined by ArbitrationTimeout has passed for an external cluster manager application to perform arbitration instead of handling arbitration internally. This can be done by setting Arbitration = WaitExternal in the [ndbd default] section of the config.ini file. For best results with the WaitExternal setting, it is recommended that ArbitrationTimeout be 2 times as long as the interval required by the external cluster manager to perform arbitration.

      Important

      This parameter should be used only in the [ndbd default] section of the cluster configuration file. The behavior of the cluster is unspecified when Arbitration is set to different values for individual data nodes.

    Buffering and logging.  Several [ndbd] configuration parameters enable the advanced user to have more control over the resources used by node processes and to adjust various buffer sizes at need.

    These buffers are used as front ends to the file system when writing log records to disk. If the node is running in diskless mode, these parameters can be set to their minimum values without penalty due to the fact that disk writes are “faked” by the NDB storage engine's file system abstraction layer.

    • UndoIndexBuffer

      Restart Type node
        Permitted Values
      Type numeric
      Default 2M
      Range 1M-4G

      The UNDO index buffer, whose size is set by this parameter, is used during local checkpoints. The NDB storage engine uses a recovery scheme based on checkpoint consistency in conjunction with an operational REDO log. To produce a consistent checkpoint without blocking the entire system for writes, UNDO logging is done while performing the local checkpoint. UNDO logging is activated on a single table fragment at a time. This optimization is possible because tables are stored entirely in main memory.

      The UNDO index buffer is used for the updates on the primary key hash index. Inserts and deletes rearrange the hash index; the NDB storage engine writes UNDO log records that map all physical changes to an index page so that they can be undone at system restart. It also logs all active insert operations for each fragment at the start of a local checkpoint.

      Reads and updates set lock bits and update a header in the hash index entry. These changes are handled by the page-writing algorithm to ensure that these operations need no UNDO logging.

      This buffer is 2MB by default. The minimum value is 1MB, which is sufficient for most applications. For applications doing extremely large or numerous inserts and deletes together with large transactions and large primary keys, it may be necessary to increase the size of this buffer. If this buffer is too small, the NDB storage engine issues internal error code 677 (Index UNDO buffers overloaded).

      Important

      It is not safe to decrease the value of this parameter during a rolling restart.

    • UndoDataBuffer

      Restart Type node
        Permitted Values
      Type numeric
      Default 16M
      Range 1M-4G

      This parameter sets the size of the UNDO data buffer, which performs a function similar to that of the UNDO index buffer, except the UNDO data buffer is used with regard to data memory rather than index memory. This buffer is used during the local checkpoint phase of a fragment for inserts, deletes, and updates.

      Because UNDO log entries tend to grow larger as more operations are logged, this buffer is also larger than its index memory counterpart, with a default value of 16MB.

      This amount of memory may be unnecessarily large for some applications. In such cases, it is possible to decrease this size to a minimum of 1MB.

      It is rarely necessary to increase the size of this buffer. If there is such a need, it is a good idea to check whether the disks can actually handle the load caused by database update activity. A lack of sufficient disk space cannot be overcome by increasing the size of this buffer.

      If this buffer is too small and gets congested, the NDB storage engine issues internal error code 891 (Data UNDO buffers overloaded).

      Important

      It is not safe to decrease the value of this parameter during a rolling restart.

    • RedoBuffer

      Restart Type node
        Permitted Values
      Type numeric
      Default 8M
      Range 1M-4G

      All update activities also need to be logged. The REDO log makes it possible to replay these updates whenever the system is restarted. The NDB recovery algorithm uses a “fuzzy” checkpoint of the data together with the UNDO log, and then applies the REDO log to play back all changes up to the restoration point.

      RedoBuffer sets the size of the buffer in which the REDO log is written. In MySQL Cluster NDB 6.4.3 and earlier, the default value is 8MB; beginning with MySQL Cluster NDB 7.0.4, the default is 32MB. The minimum value is 1MB.

      If this buffer is too small, the NDB storage engine issues error code 1221 (REDO log buffers overloaded).

      Important

      It is not safe to decrease the value of this parameter during a rolling restart.

    Controlling log messages.  In managing the cluster, it is very important to be able to control the number of log messages sent for various event types to stdout. For each event category, there are 16 possible event levels (numbered 0 through 15). Setting event reporting for a given event category to level 15 means all event reports in that category are sent to stdout; setting it to 0 means that there will be no event reports made in that category.

    By default, only the startup message is sent to stdout, with the remaining event reporting level defaults being set to 0. The reason for this is that these messages are also sent to the management server's cluster log.

    An analogous set of levels can be set for the management client to determine which event levels to record in the cluster log.

    • LogLevelStartup

      Restart Type node
        Permitted Values
      Type numeric
      Default 1
      Range 0-15

      The reporting level for events generated during startup of the process.

      The default level is 1.

    • LogLevelShutdown

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated as part of graceful shutdown of a node.

      The default level is 0.

    • LogLevelStatistic

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for statistical events such as number of primary key reads, number of updates, number of inserts, information relating to buffer usage, and so on.

      The default level is 0.

    • LogLevelCheckpoint

      Restart Type initial, node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated by local and global checkpoints.

      The default level is 0.

    • LogLevelNodeRestart

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated during node restart.

      The default level is 0.

    • LogLevelConnection

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated by connections between cluster nodes.

      The default level is 0.

    • LogLevelError

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated by errors and warnings by the cluster as a whole. These errors do not cause any node failure but are still considered worth reporting.

      The default level is 0.

    • LogLevelCongestion

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated by congestion. These errors do not cause node failure but are still considered worth reporting.

      The default level is 0.

    • LogLevelInfo

      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-15

      The reporting level for events generated for information about the general state of the cluster.

      The default level is 0.

    • MemReportFrequency

      Version Introduced 5.1.16
      Restart Type node
        Permitted Values (>= 5.1.16)
      Type numeric
      Default 0
      Range 0-4G

      This parameter controls how often data node memory usage reports are recorded in the cluster log; it is an integer value representing the number of seconds between reports.

      Each data node's data memory and index memory usage is logged as both a percentage and a number of 32 KB pages of the DataMemory and IndexMemory, respectively, set in the config.ini file. For example, if DataMemory is equal to 100 MB, and a given data node is using 50 MB for data memory storage, the corresponding line in the cluster log might look like this:

      2006-12-24 01:18:16 [MgmSrvr] INFO -- Node 2: Data usage is 50%(1280 32K pages of total 2560)
      

      MemReportFrequency is not a required parameter. If used, it can be set for all cluster data nodes in the [ndbd default] section of config.ini, and can also be set or overridden for individual data nodes in the corresponding [ndbd] sections of the configuration file. The minimum value—which is also the default value—is 0, in which case memory reports are logged only when memory usage reaches certain percentages (80%, 90%, and 100%), as mentioned in the discussion of statistics events in Section 17.5.4.2, “MySQL Cluster Log Events”.

      This parameter was added in MySQL Cluster 5.1.16 and MySQL Cluster NDB 6.1.0.

    • StartupStatusReportFrequency

      Version Introduced 5.1.30-ndb-6.4.0
      Restart Type node
        Permitted Values
      Type numeric

      When a data node is started with the --initial, it initializes the redo log file during Start Phase 4 (see Section 17.5.1, “Summary of MySQL Cluster Start Phases”). When very large values are set for NoOfFragmentLogFiles, FragmentLogFileSize, or both, this initialization can take a long time. Previous to MySQL Cluster NDB 6.4.0, only the beginning and end of the redo log file initialization process were logged. Beginning with this version, it is possible to force reports on the progress of this process to be logged periodically, by means of the StartupStatusReportFrequency configuration parameter. In this case, progress is reported in the cluster log, in terms of both the number of files and the amount of space that have been initialized, as shown here:

      2009-06-20 16:39:23 [MgmSrvr] INFO -- Node 1: Local redo log file initialization status:
      #Total files: 80, Completed: 60
      #Total MBytes: 20480, Completed: 15557
      2009-06-20 16:39:23 [MgmSrvr] INFO -- Node 2: Local redo log file initialization status:
      #Total files: 80, Completed: 60
      #Total MBytes: 20480, Completed: 15570
      

      These reports are logged each StartupStatusReportFrequency seconds during Start Pahe 4. If StartupStatusReportFrequency is 0 (the default), then reports are written to the cluster log only when at the beginning and at the completion of the redo log file initialization process.

    Backup parameters.  The [ndbd] parameters discussed in this section define memory buffers set aside for execution of online backups.

    • BackupDataBufferSize

      Restart Type node
        Permitted Values
      Type numeric
      Default 2M
      Range 0-4G

      In creating a backup, there are two buffers used for sending data to the disk. The backup data buffer is used to fill in data recorded by scanning a node's tables. Once this buffer has been filled to the level specified as BackupWriteSize (see below), the pages are sent to disk. While flushing data to disk, the backup process can continue filling this buffer until it runs out of space. When this happens, the backup process pauses the scan and waits until some disk writes have completed freed up memory so that scanning may continue.

      In MySQL Cluster NDB 6.4.3 and earlier, the default value is 2MB; in MySQL Cluster NDB 7.0.4 and later, it is 16MB.

    • BackupLogBufferSize

      Restart Type node
        Permitted Values
      Type numeric
      Default 2M
      Range 0-4G

      The backup log buffer fulfills a role similar to that played by the backup data buffer, except that it is used for generating a log of all table writes made during execution of the backup. The same principles apply for writing these pages as with the backup data buffer, except that when there is no more space in the backup log buffer, the backup fails. For that reason, the size of the backup log buffer must be large enough to handle the load caused by write activities while the backup is being made. See Section 17.5.3.3, “Configuration for MySQL Cluster Backups”.

      The default value for this parameter should be sufficient for most applications. In fact, it is more likely for a backup failure to be caused by insufficient disk write speed than it is for the backup log buffer to become full. If the disk subsystem is not configured for the write load caused by applications, the cluster is unlikely to be able to perform the desired operations.

      It is preferable to configure cluster nodes in such a manner that the processor becomes the bottleneck rather than the disks or the network connections.

      In MySQL Cluster NDB 6.4.3 and earlier, the default value is 2MB; in MySQL Cluster NDB 7.0.4 and later, it is 16MB.

    • BackupMemory

      Restart Type node
        Permitted Values
      Type numeric
      Default 4M
      Range 0-4G

      This parameter is simply the sum of BackupDataBufferSize and BackupLogBufferSize.

      In MySQL Cluster NDB 6.4.3 and earlier, the default value was 2MB + 2MB = 4MB; in MySQL Cluster NDB 7.0.4 and later, it is 16MB + 16MB = 32MB.

      Important

      If BackupDataBufferSize and BackupLogBufferSize taken together exceed the default value for BackupMemory, then this parameter must be set explicitly in the config.ini file to their sum.

    • BackupReportFrequency

      Version Introduced 5.1.19-ndb-6.2.3
      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-4G

      This parameter controls how often backup status reports are issued in the management client during a backup, as well as how often such reports are written to the cluster log (provided cluster event logging is configured to allow it—see Section 17.3.2.6, “Defining MySQL Cluster Data Nodes”). BackupReportFrequency represents the time in seconds between backup status reports.

      The default value is 0.

      This parameter was added in MySQL Cluster NDB 6.2.3.

    • BackupWriteSize

      Restart Type node
        Permitted Values
      Type numeric
      Default 32K
      Range 2K-4G

      This parameter specifies the default size of messages written to disk by the backup log and backup data buffers.

      In MySQL Cluster 6.4.3 and earlier, the default value for this parameter was 32KB; beginning with MySQL Cluster NDB 7.0.4, it is 256KB.

    • BackupMaxWriteSize

      Restart Type node
        Permitted Values
      Type numeric
      Default 256K
      Range 2K-4G

      This parameter specifies the maximum size of messages written to disk by the backup log and backup data buffers.

      In MySQL Cluster 6.4.3 and earlier, the default value for this parameter was 256KB; beginning with MySQL Cluster NDB 7.0.4, it is 1MB.

    Important

    When specifying these parameters, the following relationships must hold true. Otherwise, the data node will be unable to start.

    • BackupDataBufferSize >= BackupWriteSize + 188KB

    • BackupLogBufferSize >= BackupWriteSize + 16KB

    • BackupMaxWriteSize >= BackupWriteSize

    Realtime Performance Parameters

    The [ndbd] parameters discussed in this section are used in scheduling and locking of threads to specific CPUs on multiprocessor data node hosts. They were introduced in MySQL Cluster NDB 6.3.4.

    Note

    To make use of these parameters, the data node process must be run as system root.

    • LockExecuteThreadToCPU

      Version Introduced 5.1.19-ndb-6.3.4
      Restart Type node
        Permitted Values
      Type numeric
      Default 64K
      Range 0-64K

      Previous to MySQL Cluster NDB 7.0.  This parameter specifies the ID of the CPU assigned to handle the NDBCLUSTER execution thread. The value of this parameter is an integer in the range 0 to 65535 (inclusive). The default is 65535.

      MySQL Cluster NDB 7.0 and later (beginning with MySQL Cluster NDB 6.4.0).  When used with ndbd, this parameter (now a string) specifies the ID of the CPU assigned to handle the NDBCLUSTER execution thread. When used with ndbmtd, the value of this parameter is a comma-separated list of CPU IDs assigned to handle execution threads. Each CPU ID in the list should be an integer in the range 0 to 65535 (inclusive). The number of IDs specified should match the number of execution threads determined by MaxNoOfExecutionThreads. There is no default value.

    • LockMaintThreadsToCPU

      Version Introduced 5.1.19-ndb-6.3.4
      Restart Type node
        Permitted Values
      Type numeric
      Default 64K
      Range 0-64K

      This parameter specifies the ID of the CPU assigned to handle NDBCLUSTER maintenance threads.

      The value of this parameter is an integer in the range 0 to 65535 (inclusive). This parameter was added in MySQL Cluster NDB 6.3.4. Prior to MySQL Cluster NDB 6.4.0, the default is 65535; in MySQL Cluster NDB 7.0 and later MySQL Cluster release series, there is no default value.

    • RealtimeScheduler

      Version Introduced 5.1.19-ndb-6.3.4
      Restart Type node
        Permitted Values
      Type boolean
      Default false
      Range -

      Setting this parameter to 1 enables real-time scheduling of NDBCLUSTER threads.

      The default is 0 (scheduling disabled).

    • SchedulerExecutionTimer

      Version Introduced 5.1.22-ndb-6.3.4
      Restart Type node
        Permitted Values
      Type numeric
      Default 50
      Range 0-11000

      This parameter specifies the time in microseconds for threads to be executed in the scheduler before being sent. Setting it to 0 minimizes the response time; to achieve higher throughput, you can increase the value at the expense of longer response times.

      The default is 50 μsec, which our testing shows to increase throughput slightly in high-load cases without materially delaying requests.

      This parameter was added in MySQL Cluster NDB 6.3.4.

    • SchedulerSpinTimer

      Version Introduced 5.1.22-ndb-6.3.4
      Restart Type node
        Permitted Values
      Type numeric
      Default 0
      Range 0-500

      This parameter specifies the time in microseconds for threads to be executed in the scheduler before sleeping.

      The default value is 0.

    Disk Data Configuration Parameters.  Configuration parameters affecting Disk Data behavior include the following:

    • DiskPageBufferMemory

      This determines the amount of space used for caching pages on disk, and is set in the [ndbd] or [ndbd default] section of the config.ini file. It is measured in bytes. Each page takes up 32 KB. This means that Cluster Disk Data storage always uses N * 32 KB memory where N is some nonnegative integer.

      The default value for this parameter is 64M (2000 pages of 32 KB each).

      This parameter was added in MySQL 5.1.6.

    • SharedGlobalMemory

      This determines the amount of memory that is used for log buffers, disk operations (such as page requests and wait queues), and metadata for tablespaces, log file groups, UNDO files, and data files. It can be set in the [ndbd] or [ndbd default] section of the config.ini configuration file, and is measured in bytes.

      The default value is 20M.

      This parameter was added in MySQL 5.1.6.

    • DiskIOThreadPool

      This parameter determines the number of unbound threads used for Disk Data file access. Before DiskIOThreadPool was introduced, exactly one thread was spawned for each Disk Data file, which could lead to performance issues, particularly when using very large data files. With DiskIOThreadPool, you can—for example—access a single large data file using several threads working in parallel.

      Currently, this parameter applies to Disk Data I/O threads only, but we plan in the future to make the number of such threads configurable for in-memory data as well.

      The optimum value for this parameter depends on your hardware and configuration, and includes these factors:

      • Physical distribution of Disk Data files.  You can obtain better performance by placing data files, undo log files, and the data node filesystem on separate physical disks. If you do this with some or all of these sets of files, then you can set DiskIOThreadPool higher to allow separate threads to handle the files on each disk.

      • Disk performance and types.  The number of threads that can be accommodated for Disk Data file handling is also dependent on the speed and throughput of the disks. Faster disks and higher throughput allow for more disk I/O threads. Our test results indicate that solid-state disk drives can handle many more disk I/O threads than conventional disks, and thus higher values for DiskIOThreadPool.

      This parameter was added in MySQL Cluster NDB 6.4.0. Previous to MySQL Cluster NDB 6.4.3, it was named ThreadPool. Previous to MySQL Cluster NDB 7.0.7, the default value was 8. Beginning with MySQL Cluster NDB 7.0.7 and MySQL Cluster NDB 7.1.0, the default is 2.

    • Disk Data filesystem parameters.  The parameters in the following list were added in MySQL Cluster NDB 6.2.17, 6.3.22, and 6.4.3 to make it possible to place MySQL Cluster Disk Data files in specific directories without the need for using symbolic links.

      • FileSystemPathDD

        If this parameter is specified, then MySQL Cluster Disk Data data files and undo log files are placed in the indicated directory. This can be overridden for data files, undo log files, or both, by specifying values for FileSystemPathDataFiles, FileSystemPathUndoFiles, or both, as explained for these parameters. It can also be overridden for data files by specifying a path in the ADD DATAFILE clause of a CREATE TABLESPACE or ALTER TABLESPACE statement, and for undo log files by specifying a path in the ADD UNDOFILE clause of a CREATE LOGFILE GROUP or ALTER LOGFILE GROUP statement. If FileSystemPathDD is not specified, then FileSystemPath is used.

        If a FileSystemPathDD directory is specified for a given data node (including the case where the parameter is specified in the [ndbd default] section of the config.ini file), then starting that data node with --initial causes all files in the directory to be deleted.

      • FileSystemPathDataFiles

        If this parameter is specified, then MySQL Cluster Disk Data data files are placed in the indicated directory. This overrides any value set for FileSystemPathDD. This parameter can be overridden for a given data file by specifying a path in the ADD DATAFILE clause of a CREATE TABLESPACE or ALTER TABLESPACE statement used to create that data file. If FileSystemPathDataFiles is not specified, then FileSystemPathDD is used (or FileSystemPath, if FileSystemPathDD has also not been set).

        If a FileSystemPathDataFiles directory is specified for a given data node (including the case where the parameter is specified in the [ndbd default] section of the config.ini file), then starting that data node with --initial causes all files in the directory to be deleted.

      • FileSystemPathUndoFiles

        If this parameter is specified, then MySQL Cluster Disk Data undo log files are placed in the indicated directory. This overrides any value set for FileSystemPathDD. This parameter can be overridden for a given data file by specifying a path in the ADD UNDO clause of a CREATE LOGFILE GROUP or CREATE LOGFILE GROUP statement used to create that data file. If FileSystemPathUndoFiles is not specified, then FileSystemPathDD is used (or FileSystemPath, if FileSystemPathDD has also not been set).

        If a FileSystemPathUndoFiles directory is specified for a given data node (including the case where the parameter is specified in the [ndbd default] section of the config.ini file), then starting that data node with --initial causes all files in the directory to be deleted.

      For more information, see Section 17.5.10.1, “MySQL Cluster Disk Data Objects”.

    • Disk Data object creation parameters.  The next two parameters enable you—when starting the cluster for the first time—to cause a Disk Data log file group, tablespace, or both, to be created without the use of SQL statements.

      • InitialLogFileGroup

        This parameter can be used to specify a log file group that is created when performing an initial start of the cluster. InitialLogFileGroup is specified as shown here:

        InitialLogFileGroup = [name=name;] [undo_buffer_size=size;] file-specification-list
        
        file-specification-list:
            file-specification[; file-specification[; ...]]
        
        file-specification:
            filename:size
        

        The name of the log file group is optional and defaults to DEFAULT_LG. The undo_buffer_size is also optional; if omitted, it defaults to 256M (256 megabytes). Each file-specification corresponds to an undo log file, and at least one must be specified in the file-specification-list. Undo log files are placed according to any values that have been set for FileSystemPath, FileSystemPathDD, and FileSystemPathUndoFiles, just as if they had been created as the result of a CREATE LOGFILE GROUP or ALTER LOGFILE GROUP statement.

        Consider the following example:

        InitialLogFileGroup = name=LG1; undo_buffer_size=128M; undo1.log:250M; undo2.log:150M
        

        This is equivalent to the following SQL statements:

        CREATE LOGFILE GROUP LG1
            ADD UNDOFILE 'undo1.log'
            INITIAL_SIZE 250M
            UNDO_BUFFER_SIZE 128M
            ENGINE NDBCLUSTER;
        
        ALTER LOGFILE GROUP LG1
            ADD UNDOFILE 'undo2.log'
            INITIAL_SIZE 150M
            ENGINE NDBCLUSTER;
        

        This logfile group is created when the data nodes are started with --initial.

        This parameter, if used, should always be set in the [ndbd default] section of the config.ini file. The behavior of a MySQL Cluster when different values are set on different data nodes is not defined.

      • InitialTablespace

        This parameter can be used to specify a MySQL Cluster Disk Data tablespace that is created when performing an initial start of the cluster. InitialTablespace is specified as shown here:

        InitialTablespace = [name=name;] [extent_size=size;] file-specification-list
        

        The name of the tablespace is optional and defaults to DEFAULT_TS. The extent_size is also optional; it defaults to 1M (1 megabyte). The file-specification-list uses the same syntax as shown with the InitialLogfileGroup parameter, the only difference being that each file-specification used with InitialTablespace corresponds to a data file. At least one must be specified in the file-specification-list. Data files are placed according to any values that have been set for FileSystemPath, FileSystemPathDD, and FileSystemPathDataFiles, just as if they had been created as the result of a CREATE TABLESPACE or ALTER TABLESPACE statement.

        For example, consider the following line specifying InitialTablespace in the [ndbd default] section of the config.ini file (as with InitialLogfileGroup, this parameter should always be set in the [ndbd default] section, as the behavior of a MySQL Cluster when different values are set on different data nodes is not defined):

        InitialTablespace = name=TS1; extent_size=8M; data1.dat:2G; data2.dat:4G
        

        This is equivalent to the following SQL statements:

        CREATE TABLESPACE TS1
            ADD DATAFILE 'data1.dat'
            EXTENT_SIZE 8M
            INITIAL_SIZE 2G
            ENGINE NDBCLUSTER;
        
        ALTER TABLESPACE TS1
            ADD UNDOFILE 'data2.dat'
            INITIAL_SIZE 4G
            ENGINE NDBCLUSTER;
        

        This tablespace is created when the data nodes are started with --initial, and can be used whenever creating MySQL Cluster Disk Data tables thereafter.

    Disk Data and GCP Stop errors.  Errors encountered when using Disk Data tables such as Node nodeid killed this node because GCP stop was detected (error 2303) are often referred to as “GCP stop errors”. Such errors occur when the redo log is not flushed to disk quickly enough; this is usually due to slow disks and insufficient disk throughput.

    You can help prevent these errors from occurring by using faster disks, and by placing Disk Data files on a separate disk from the data node filesystem. Reducing the value of TimeBetweenGlobalCheckpoints tends to decrease the amount of data to be written for each global checkpoint, and so may provide some protection against redo log buffer overflows when trying to write a global checkpoint; however, reducing this value also allows less time in which to write the GCP, so this must be done with caution.

    In addition, adjusting the cluster configuration as discussed here can also help:

    • MySQL Cluster NDB 6.2 and 6.3.  When working with large amounts of data on disk under high load, the default value for DiskPageBufferMemory may not be large enough. In such cases, you should increase its value to include most of the memory available to the data nodes after accounting for index memory, data memory, internal buffers, and memory needed by the data node host operating system.

      You can use this formula as a guide:

      DiskPageBufferMemory
        = 0.8
          x (
              [total memory]
                - ([operating system memory] + [buffer memory] + DataMemory + IndexMemory)
            )
      

      Once you have established that sufficient memory is reserved for DataMemory, IndexMemory, NDB internal buffers, and operating system overhead, it is possible (and sometimes desirable) to allocate more than the above amount of the remainder to DiskPageBufferMemory.

    • MySQL Cluster NDB 7.X.  In addition to the considerations given for DiskPageBufferMemory as explained in the previous item, it is also very important that the DiskIOThreadPool configuration parameter be set correctly; having DiskIOThreadPool set too high is very likely to cause GCP stop errors (Bug#37227).

    Parameters for configuring send buffer memory allocation (MySQL Cluster NDB 7.0).  Beginning with MySQL Cluster NDB 6.4.0, send buffer memory is allocated dynamically from a memory pool shared between all transporters, which means that the size of the send buffer can be adjusted as necessary. (Previously, the NDB kernel used a fixed-size send buffer for every node in the cluster, which was allocated when the node started and could not be changed while the node was running.) The following data node configuration parameters were added in MySQL Cluster NDB 6.4.0 to permit the setting of limits on this memory allocation; this change is reflected by the addition of the configuration parameters TotalSendBufferMemory and OverLoadLimit, as well as a change in how the existing SendBufferMemory configuration parameter is used. For more information, see Section 17.3.2.13, “Configuring MySQL Cluster Send Buffer Parameters”.

    • TotalSendBufferMemory

      This parameter is available beginning with MySQL Cluster NDB 6.4.0. It is used to determine the total amount of memory to allocate on this node for shared send buffer memory among all configured transporters.

      If this parameter is set, its minimum allowed value is 256K; the maxmimum is 4294967039.

    • ReservedSendBufferMemory

      This parameter is present in NDBCLUSTER source code beginning with MySQL Cluster NDB 6.4.0. However, it is not currently enabled.

    For more detailed information about the behavior and use of TotalSendBufferMemory and about configuring send buffer memory parameters in MySQL Cluster NDB 6.4.0 and later, see Section 17.3.2.13, “Configuring MySQL Cluster Send Buffer Parameters”.

    Note

    Previous to MySQL Cluster NDB 7.0, to add new data nodes to a MySQL Cluster, it is necessary to shut down the cluster completely, update the config.ini file, and then restart the cluster (that is, you must perform a system restart). All data node processes must be started with the --initial option.

    Beginning with MySQL Cluster NDB 7.0, it is possible to add new data node groups to a running cluster online. See Section 17.5.11, “Adding MySQL Cluster Data Nodes Online”, for more information.