[amodhakal]

dict_stats_fetch_index_stats_step() uses UINT64_UNDEFINED (18446744073709551615) as a sentinel for missing stats, but nothing stopped a user from writing that exact value into mysql.innodb_index_stats.stat_value, causing an assertion failure.

Add a CHECK constraint, innodb_index_stats_stat_value_defined, rejecting the sentinel value on write, and an MTR test covering the repro.

Fixes https://jira.mariadb.org/browse/MDEV-40840

[gkodinov]

Thank you for your contribution! This is a preliminary review.

My recommendation is to please consider making the info printing an error. What good is it to silently ignore values that the user supplied?

But, I'll leave this to the final reviewer. Formally, it's ok to push as is.
Please stand by for the final review.

[gkodinov]

FYI: According to our development cycle we work on bugs In the following periods 15 Mar-30 Apr, 15 Jun-30 Jul, 15 Sep-30 Oct and 15 Dec-31 Jan. So, please, expect to get a review somewhere between these two dates and the goal is to have your PR merged before the second date

[gkodinov]

LGTM. Please stand by for the final review.

[Thirunarayanan]

Please rebase the branch to 11.4
Can't we have simple statement like

 alter table innodb_index_stats add constraint if not exists innodb_index_stats_stat_value_defined check (stat_value <> 18446744073709551615);