Flashback

Flashback is a feature that allows instances, databases or tables to be rolled back to an old snapshot.

Flashback is currently supported only over DML statements (INSERT, DELETE, UPDATE). An upcoming version of MariaDB will add support for flashback over DDL statements (DROP, TRUNCATE, ALTER, etc.) by copying or moving the current table to a reserved and hidden database, and then copying or moving back when using flashback. See MDEV-10571.

Flashback is achieved in MariaDB Server using existing support for full image format binary logs (binlog_row_image=FULL), so it supports all engines.

The real work of Flashback is done by mariadb-binlog with --flashback. This causes events to be translated: INSERT to DELETE, DELETE to INSERT, and for UPDATEs, the before and after images are swapped.

When executing mariadb-binlog with --flashback, the Flashback events will be stored in memory. You should make sure your server has enough memory for this feature.

Arguments

• mariadb-binlog has the option --flashback or -B that will let it work in flashback mode.
• mariadbd has the option --flashback that enables the binary log and sets binlog_format=ROW. It is not mandatory to use this option if you have already enabled those options directly.

Example

With a table "mytable" in database "test", you can compare the output with --flashback and without.

 mariadb-binlog /var/lib/mysql/mysql-bin.000001 -vv -d test -T mytable \
    --start-datetime="2013-03-27 14:54:00" > review.sql

 mariadb-binlog /var/lib/mysql/mysql-bin.000001 -vv -d test -T mytable \
    --start-datetime="2013-03-27 14:54:00" --flashback > flashback.sql

If you know the exact position, --start-position can be used instead of --start-datetime.

Then, by importing the output file (mariadb < flashback.sql), you can flash your database/table back to the specified time or position.

Common Use Case

A common use case for Flashback is the following scenario:

• You have one primary and two replicas, one started with --flashback (i.e. with binary logging enabled, using binlog_format=ROW, and binlog_row_image=FULL).
• Something goes wrong on the primary (like a wrong update or delete) and you would like to revert to a state of the database (or just a table) at a certain point in time.
• Remove the flashback-enabled replica from replication.
• Invoke mariadb-binlog to find the exact log position of the first offending operation after the state you want to revert to.
• Run mariadb-binlog --flashback --start-position=xyz | mariadb to pipe the output of mariadb-binlog directly to the mariadb client, or save the output to a file and then direct the file to the command-line client.