The binary log contains “events” that describe database changes such as table creation operations or changes to table data. It also contains events for statements that potentially could have made changes (for example, a
DELETEwhich matched no rows), unless row-based logging is used. The binary log also contains information about how long each statement took that updated data. The binary log has two important purposes:
For replication, the binary log is used on master replication servers as a record of the statements to be sent to slave servers. The master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master. See Section 16.2, “Replication Implementation”.
Certain data recovery operations require use of the binary log. After a backup has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup. See Section 6.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.
Running a server with binary logging enabled makes performance slightly slower. However, the benefits of the binary log in allowing you to set up replication and for restore operations generally outweigh this minor performance decrement.
For information about server options and variables affecting the operation of binary logging, see Section 18.104.22.168, “Binary Log Options and Variables”.
The binary log is not used for statements such as
SHOWthat do not modify data. If you want to log all statements (for example, to identify a problem query), use the general query log. See Section 5.2.3, “The General Query Log”.
The binary log should be protected because logged statements might contain passwords. See Section 22.214.171.124, “Administrator Guidelines for Password Security”.
The format of the events recorded in the binary log is dependent on the binary logging format. Three format types are supported, row-based logging, statement-based logging and mixed-base logging. The binary logging format used depends on the MySQL version. For more information on logging formats, see Section 126.96.36.199, “Binary Logging Formats”.
MySQL Enterprise. The binary log can also be used to track significant DDL events. Analyzing the binary log in this way is an integral part of the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.
To enable the binary log, start the server with the
--log-bin[=option. If no
base_namevalue is given, the default name is the value of the
pid-fileoption (which by default is the name of host machine) followed by
-bin. If the basename is given, the server writes the file in the data directory unless the basename is given with a leading absolute path name to specify a different directory. It is recommended that you specify a basename; see Section B.5.8.2, “Additional Known Issues”, for the reason.
From MySQL 5.1.18 through 5.1.22, “mysql” was used when no
base_namewas specified. Also in these versions, a path given as part of the
--log-binoptions was treated as absolute rather than relative. The previous behaviors were restored in MySQL 5.1.23. (See Bug#28603 and Bug#28597.)
If you supply an extension in the log name (for example,
--log-bin=), the extension is silently removed and ignored.
mysqld appends a numeric extension to the binary log basename to generate binary log file names. The number increases each time the server creates a new log file, thus creating an ordered series of files. The server creates a new file in the series each time it starts or flushes the logs. The server also creates a new binary log file automatically after the current log's size reaches
max_binlog_size. A binary log file may become larger than
max_binlog_sizeif you are using large transactions because a transaction is written to the file in one piece, never split between files.
To keep track of which binary log files have been used, mysqld also creates a binary log index file that contains the names of all used binary log files. By default, this has the same basename as the binary log file, with the extension
'.index'. You can change the name of the binary log index file with the
--log-bin-index[=option. You should not manually edit this file while mysqld is running; doing so would confuse mysqld.
The term “binary log file” generally denotes an individual numbered file containing database events. The term “binary log” collectively denotes the set of numbered binary log files plus the index file.
The server evaluates the
--binlog-ignore-dboptions in the same way as it does the
--replicate-ignore-dboptions. For information about how this is done, see Section 188.8.131.52, “Evaluation of Database-Level Replication and Binary Logging Options”.
A replication slave server by default does not write to its own binary log any data modifications that are received from the replication master. To log these modifications, start the slave with the
--log-slave-updatesoption in addition to the
--log-binoption (see Section 184.108.40.206, “Replication Slave Options and Variables”). This is done when a slave is also to act as a master to other slaves in chained replication.
You can delete all binary log files with the
RESET MASTERstatement, or a subset of them with
PURGE BINARY LOGS. See Section 220.127.116.11, “
RESETSyntax”, and Section 18.104.22.168, “
PURGE BINARY LOGSSyntax”.
If you are using replication, you should not delete old binary log files on the master until you are sure that no slave still needs to use them. For example, if your slaves never run more than three days behind, once a day you can execute mysqladmin flush-logs on the master and then remove any logs that are more than three days old. You can remove the files manually, but it is preferable to use
PURGE BINARY LOGS, which also safely updates the binary log index file for you (and which can take a date argument). See Section 22.214.171.124, “
PURGE BINARY LOGSSyntax”.
You can display the contents of binary log files with the mysqlbinlog utility. This can be useful when you want to reprocess statements in the log for a recovery operation. For example, you can update a MySQL server from the binary log as follows:
log_file| mysql -h
mysqlbinlog also can be used to display replication slave relay log file contents because they are written using the same format as binary log files. For more information on the mysqlbinlog utility and how to use it, see Section 4.6.7, “mysqlbinlog — Utility for Processing Binary Log Files”. For more information about the binary log and recovery operations, see Section 6.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.
Binary logging is done immediately after a statement completes but before any locks are released or any commit is done. This ensures that the log is logged in execution order.
Updates to nontransactional tables are stored in the binary log immediately after execution. In MySQL 5.1.22 and earlier versions of MySQL 5.1, an
UPDATEstatement using a stored function that modified a nontransactional table was not logged if it failed, and an
INSERT ... ON DUPLICATE KEY UPDATEstatement that encountered a duplicate key constraint—but did not actually change any data—was not logged. Beginning with MySQL 5.1.23, both of these statements are written to the binary log. (Bug#23333)
Within an uncommitted transaction, all updates (
INSERT) that change transactional tables such as
InnoDBtables are cached until a
COMMITstatement is received by the server. At that point, mysqld writes the entire transaction to the binary log before the
Modifications to nontransactional tables cannot be rolled back. If a transaction that is rolled back includes modifications to nontransactional tables, the entire transaction is logged with a
ROLLBACKstatement at the end to ensure that the modifications to those tables are replicated.
When a thread that handles the transaction starts, it allocates a buffer of
binlog_cache_sizeto buffer statements. If a statement is bigger than this, the thread opens a temporary file to store the transaction. The temporary file is deleted when the thread ends.
Binlog_cache_usestatus variable shows the number of transactions that used this buffer (and possibly a temporary file) for storing statements. The
Binlog_cache_disk_usestatus variable shows how many of those transactions actually had to use a temporary file. These two variables can be used for tuning
binlog_cache_sizeto a large enough value that avoids the use of temporary files.
max_binlog_cache_sizesystem variable (default 4GB, which is also the maximum) can be used to restrict the total size used to cache a multiple-statement transaction. If a transaction is larger than this many bytes, it fails and rolls back. The minimum value is 4096.
If you are using the binary log and row based logging, concurrent inserts are converted to normal inserts for
CREATE ... SELECTor
INSERT ... SELECTstatement. This is done to ensure that you can re-create an exact copy of your tables by applying the log during a backup operation. If you are using statement-based logging, the original statement is written to the log.
The binary log format has some known limitations that can affect recovery from backups. See Section 16.4.1, “Replication Features and Issues”.
Binary logging for stored programs is done as described in Section 19.7, “Binary Logging of Stored Programs”.
Note that the binary log format differs in MySQL 5.1 from previous versions of MySQL, due to enhancements in replication. See Section 16.4.2, “Replication Compatibility Between MySQL Versions”.
Writes to the binary log file and binary log index file are handled in the same way as writes to
MyISAMtables. See Section B.5.4.3, “How MySQL Handles a Full Disk”.
By default, the binary log is not synchronized to disk at each write. So if the operating system or machine (not only the MySQL server) crashes, there is a chance that the last statements of the binary log are lost. To prevent this, you can make the binary log be synchronized to disk after every
Nwrites to the binary log, with the
sync_binlogsystem variable. See Section 5.1.4, “Server System Variables”. 1 is the safest value for
sync_binlog, but also the slowest. Even with
sync_binlogset to 1, there is still the chance of an inconsistency between the table content and binary log content in case of a crash. For example, if you are using
InnoDBtables and the MySQL server processes a
COMMITstatement, it writes the whole transaction to the binary log and then commits this transaction into
InnoDB. If the server crashes between those two operations, the transaction is rolled back by
InnoDBat restart but still exists in the binary log. To resolve this, you should set
--innodb_support_xato 1. Although this option is related to the support of XA transactions in InnoDB, it also ensures that the binary log and InnoDB data files are synchronized.
For this option to provide a greater degree of safety, the MySQL server should also be configured to synchronize the binary log and the
InnoDBlogs to disk at every transaction. The
InnoDBlogs are synchronized by default, and
sync_binlog=1can be used to synchronize the binary log. The effect of this option is that at restart after a crash, after doing a rollback of transactions, the MySQL server cuts rolled back
InnoDBtransactions from the binary log. This ensures that the binary log reflects the exact data of
InnoDBtables, and so, that the slave remains in synchrony with the master (not receiving a statement which has been rolled back).
If the MySQL server discovers at crash recovery that the binary log is shorter than it should have been, it lacks at least one successfully committed
InnoDBtransaction. This should not happen if
sync_binlog=1and the disk/file system do an actual sync when they are requested to (some do not), so the server prints an error message
The binary log. In this case, this binary log is not correct and replication should be restarted from a fresh snapshot of the master's data.
file_nameis shorter than its expected size
For MySQL 5.1.20 and later (and MySQL 5.0.46 and later for backward compatibility), the session values of the following system variables are written to the binary log and honored by the replication slave when parsing the binary log: