Bug #119495 Incomplete documentation for innodb_max_purge_lag.

• Submitted: 2 Dec 21:50
• Reporter: Jean-François Gagné
• Status: Open
• Category: MySQL Server: Documentation
• Severity: S3 (Non-critical)
• OS: Any
• CPU Architecture: Any
• Tags: 8.0, 8.4, 9

[2 Dec 21:50] Jean-François Gagné

Description:
Hi,

in the documentation page "Purge Configuration" [1], I can read:

[1]: https://dev.mysql.com/doc/refman/8.4/en/innodb-purge-configuration.html

> If the innodb_max_purge_lag setting is exceeded, purge work is automatically redistributed among available purge threads.

However, in the documentation section for innodb_max_purge_lag [2], there is nothing about the purge becoming multi-threaded.

[2]: https://dev.mysql.com/doc/refman/8.4/en/innodb-parameters.html#sysvar_innodb_max_purge_lag

I would expect the documentation section for innodb_max_purge_lag to also mention the behavior about purge becoming multi-threaded.  I would also expect the contention risk, quoted below from the documentation page "Purge Configuration", to be mentioned in the documentation section for documentation page Purge Configuration.

> Too many active purge threads in this scenario can cause contention with user threads, so manage the innodb_purge_threads setting accordingly. 

The links above are for 8.4, but 8.0 and 9 documentations are also affected.

Many thanks for looking into this,

Jean-François Gagné

How to repeat:
Documentation bug, see Description for details.

Suggested fix:
Documentation bug, see Description for details.