# Information Schema INNODB\_UNDO\_LOGS Table

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The `INNODB_UNDO_LOGS` are a Percona enhancement, introduced in version [MariaDB 5.5.27](https://app.gitbook.com/s/aEnK0ZXmUbJzqQrTjFyb/community-server/old-releases/5.5/5.5.27) and removed in 10.0.
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The [Information Schema](https://mariadb.com/docs/server/reference/system-tables/information-schema) `INNODB_UNDO_LOGS` table is a Percona enchancement, and is only available for XtraDB, not InnoDB (see [XtraDB and InnoDB](https://mariadb.com/docs/server/server-usage/storage-engines/innodb)). It contains information about the InnoDB [undo log](https://mariadb.com/docs/server/server-usage/storage-engines/innodb/innodb-undo-log), with each record being an undo log segment. It was removed in [MariaDB 10.0](https://app.gitbook.com/s/aEnK0ZXmUbJzqQrTjFyb/community-server/old-releases/10.0/changes-improvements-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](https://mariadb.com/docs/server/reference/system-tables/information-schema/information-schema-tables/information-schema-innodb-tables/information-schema-innodb_trx-table) 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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