[MDEV-25689] metadata_table_reference_count, metadata_table_handles_closed are updated inconsistently; remove them Created: 2021-05-17  Updated: 2021-06-01  Resolved: 2021-05-17

Status: Closed
Project: MariaDB Server
Component/s: Storage Engine - InnoDB
Affects Version/s: 10.2, 10.3, 10.4, 10.5, 10.6
Fix Version/s: 10.6.1

Type: Bug Priority: Major
Reporter: Marko Mäkelä Assignee: Marko Mäkelä
Resolution: Fixed Votes: 0
Labels: corruption, performance

Issue Links:
Relates
relates to MDEV-15706 Remove information_schema.innodb_metr... Open
relates to MDEV-25687 trx_active_transactions is inconsiste... Closed

 Description   

The counter MONITOR_TABLE_REFERENCE (metadata_table_reference_count) is inconsistent at least since this change in MySQL 5.7.10: the member function dict_table_t::release() does not decrement the counter. Only dict_table_close() would do it.

Furthermore, it looks like the counter MONITOR_TABLE_CLOSE (metadata_table_handles_closed) is incremented unconditionally in ha_innobase::close(), while the call to increment MONITOR_TABLE_OPEN would be avoided if ha_innobase::open() returns an error earlier.

Given that no bug was filed about these inconsistencies so far (MySQL Bug #75966 was filed by an Oracle employee and fixed in MySQL 8.0), it looks like these counters are not important to users and can be removed.

The counter MONITOR_TABLE_OPEN (metadata_table_handles_opened) will be retained for now.
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