Marko Mäkelä added a comment - 2017-11-17 02:34 plinux , I would prefer not to add this table, because in a future version of MariaDB, I would like to redesign the InnoDB undo logs. There would no longer be rseg_id, but instead I would try to have an .ibu undo log file for each .ibd file. In the patch, the column zip_size should always be reported as 0. If we want this table in MariaDB (expecting the columns to be changed in a later release), I think that this column should be omitted, and the table name should be something else, such as innodb_undo or innodb_transaction_logs.

Marko Mäkelä added a comment - 2021-03-09 07:21 As noted in MDEV-25062 , we will have to change the format of undo logs to improve concurrency. My previous idea of having a separate undo log file for each tablespace would likely perform badly when a transaction is modifying multiple tables. As part of undo log format changes, we may implement some instrumentation, which would have to reflect the format of our choice.

Marko Mäkelä added a comment - 2022-03-09 11:03 While we still have not changed the transaction metadata and undo log format beyond how it was changed in MDEV-12288 and MDEV-15132 , I think that this view would be of very limited use. The columns are as follows: show create table information_schema.innodb_rseg; Table Create Table INNODB_RSEG CREATE TEMPORARY TABLE `INNODB_RSEG` ( `rseg_id` bigint(21) unsigned NOT NULL DEFAULT '0', `space_id` bigint(21) unsigned NOT NULL DEFAULT '0', `zip_size` bigint(21) unsigned NOT NULL DEFAULT '0', `page_no` bigint(21) unsigned NOT NULL DEFAULT '0', `max_size` bigint(21) unsigned NOT NULL DEFAULT '0', `curr_size` bigint(21) unsigned NOT NULL DEFAULT '0' ) ENGINE=MEMORY DEFAULT CHARSET=utf8 The rollback segment ID is conceptually a primary key. Ever since MDEV-19570 was implemented, there always are 128 rollback segments, limited by the current format of the DB_ROLL_PTR column. The space_id identifies the undo tablespace. It and page_no are constant in the TRX_SYS page since the database creation. The column zip_size should always be 0, because undo tablespaces can never use any ROW_FORMAT=COMPRESSED storage format. Above, the most interesting columns would be curr_size and max_size . Ever since MDEV-22343 removed the dictionary table SYS_TABLESPACES , the size of each tablespace (including undo tablespaces) should be reported by INFORMATION_SCHEMA.INNODB_SYS_TABLESPACES , by the columns FILE_SIZE and ALLOCATED_SIZE . That could be used for monitoring how well innodb_undo_log_truncate=ON is performing.