Information Schema INNODB_UNDO_LOGS Table

The INNODB_UNDO_LOGS table, an XtraDB enhancement, contains information about undo log segments, including transaction IDs and states.

The INNODB_UNDO_LOGS are a Percona enhancement, introduced in version MariaDB 5.5.27 and removed in 10.0.

The Information Schema INNODB_UNDO_LOGS table is a Percona enchancement, and is only available for XtraDB, not InnoDB (see XtraDB and InnoDB). It contains information about the InnoDB undo log, with each record being an undo log segment. It was removed in MariaDB 10.0.

It has the following columns:

Column	Description
TRX_ID	Unique transaction ID number, matching the value from the information_schema.INNODB_TRX table.
RSEG_ID	Rollback segment ID, matching the value from the information_schema.INNODB_RSEG table.
USEG_ID	Undo segment ID.
SEGMENT_TYPE	Indicates the operation type, for example INSERT or UPDATE.
STATE	Segment state; one of ACTIVE (contains active transaction undo log), CACHED, TO_FREE (insert undo segment can be freed), TO_PURGE (update undo segment won't be re-used and can be purged when all undo data is removed) or PREPARED (segment of a prepared transaction).
SIZE	Size in pages of the segment.

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