Binlog Event Checksums
The terms master and slave have historically been used in replication, and MariaDB has begun the process of adding primary and replica synonyms. The old terms will continue to be used to maintain backward compatibility - see MDEV-18777 to follow progress on this effort.
MariaDB includes a feature to include a checksum in binary log events.
Checksums are enabled with the binlog_checksum option. Until MariaDB 10.2.1, this was disabled by default. From MariaDB 10.2.1, the option is set to CRC32.
The variable can be changed dynamically without restarting the server. Setting the variable in any way (even to the existing value) forces a rotation of the binary log (the intention is to avoid having a single binlog where some events are checksummed and others are not).
When checksums are enabled, replicas will check events received over the network for checksum errors, and will stop with an error if a corrupt event is detected.
In addition, the server can be configured to verify checksums in two other places.
One is when reading events from the binlog on the primary, for example when sending events to a replica or for something like SHOW BINLOG EVENTS. This is controlled by option master_verify_checksum, and is thus used to detect file system corruption of the binlog files.
The other is when the replica SQL thread reads events from the relay log. This is controlled by the slave_sql_verify_checksum option, and is used to detect file system corruption of replica relay log files.
MariaDB starting with 11.4
From MariaDB 11.4, binlog checksums are computed when writing events into the statement or transaction caches, where before this was done when the caches were copied to the real binlog file. This moves the checksum computation outside of holding LOCK_log, improving scalability. See MDEV-31273.
master_verify_checksum
- Description: Verify binlog checksums when reading events from the binlog on the primary.
- Commandline:
--master_verify_checksum=[0|1] - Scope: Global
- Access Type: Can be changed dynamically
- Data Type:
bool - Default Value:
OFF (0)
slave_sql_verify_checksum
- Description: Verify binlog checksums when the replica SQL thread reads events from the relay log.
- Commandline:
--slave_sql_verify_checksum=[0|1] - Scope: Global
- Access Type: Can be changed dynamically
- Data Type:
bool - Default Value:
ON (1)
The mariadb-binlog client program by default does not verify checksums when reading a binlog file, however it can be instructed to do so with the option verify-binlog-checksum:
- Variable Name:
verify-binlog-checksum - Data Type:
bool - Default Value:
OFF
