The description below applies to MariaDB 10.1.4 and later
Sometimes there is a requirement that when some data is deleted, it is really gone. This might be the case when one stores user's personal information or some other sensitive data. Normally though, when a row is deleted, the space is only marked as free on the page. It may eventually be overwritten, but there is no guarantee when that will happen. A copy of the deleted rows may also be present in the log files.
MariaDB 10.1.3 has introduced support for InnoDB/XtraDB data scrubbing. Background threads periodically scan tablespaces and logs and remove all data that should be deleted. The number of background threads for tablespace scans is set by innodb-encryption-threads. Log scrubbing happens in a separate thread.
To configure scrubbing one can use the following variables:
| innodb-background-scrub-data-check-interval | Seconds | Check at this intervall if tablespaces needs scrubbing |
| innodb-background-scrub-data-compressed | Boolean | Enable scrubbing of compressed data by background threads |
| innodb-background-scrub-data-interval | Seconds | Scrub spaces that were last scrubbed longer than this many seconds ago. |
| innodb-background-scrub-data-uncompressed | Boolean | Enable scrubbing of uncompressed data by background threads |
| innodb-immediate-scrub-data-uncompressed | Boolean | Enable scrubbing of uncompressed data |
| innodb-scrub-log | Boolean | Enable redo log scrubbing |
| innodb-scrub-log-speed | Bytes/sec | Redo log scrubbing speed in bytes/sec |
The Information Schema INNODB_TABLESPACES_SCRUBBING table contains scrubbing information.
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https://mariadb.com/kb/en/innodb-data-scrubbing/