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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 DELETE which matched no rows , unless row-based logging is used. The binary log also contains information about how long each statement took that updated data. For replication, the binary log on a master replication server provides a record of the data changes 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.
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. 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 format of the events recorded in the binary log is dependent on the binary logging format.
The server uses several logging formats to record information in the binary log. Three format types are supported:. In row-based logging, the master writes events to the binary log that indicate how individual table rows are affected. This is called statement-based logging. A third option is also available: With mixed logging, statement-based logging is used by default , but the logging mode switches automatically to row-based in certain cases as described below.
The exact format employed depends on the version of MySQL being used. The logging format can also be set or limited by the storage engine being used. This helps to eliminate issues when replicating certain statements between a master and slave which are using different storage engines. With statement-based replication, there may be issues with replicating nondeterministic statements. Normally, MySQL logs full rows that is, all columns for both the before and after images.
However, it is not strictly necessary to include every column in both images, and we can often save disk, memory, and network usage by logging only those columns which are actually required. This variable actually takes one of three possible values, as shown in the following list:. Log all columns in both the before image and the after image.
Log only those columns in the before image that are required to identify the row to be changed; log only those columns in the after image that are actually changed. Manual config binlog in this file: The binary log has two important purposes: 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 Certain data recovery operations require use of the binary log.
These events bring databases up to date from the point of the backup Note: To log all statements for example, to identify a problem query , use the general query log Running a server with binary logging enabled makes performance slightly slower. However, the benefits of the binary log in enabling you to set up replication and for restore operations generally outweigh this minor performance decrement. The binary log is generally resilient to unexpected halts because only complete transactions are logged or read back Slave server in replication by default does not write to its own binary log any data modifications that are received from the replication master.
But sometime we want to log these modifications, slave can do that. This is done when a slave is also to act as a master to other slaves in chained replication. Binary log files mysqld appends a numeric extension to the binary log base name to generate binlog file names. 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 base name as the binary log file, with the extension. You should not manually edit this file while mysqld is running; doing so would confuse mysqld. Three format types are supported: This helps to eliminate issues when replicating certain statements between a master and slave which are using different storage engines Note: This variable actually takes one of three possible values, as shown in the following list: Binlog operations Manual config binlog in this file: