MDEV-19574 innodb_stats_method is not honored when innodb_stats_persistent=ON

[Thirunarayanan]

• The Jira issue number for this PR is: MDEV-19574

Description

Problem:

InnoDB persistent statistics doesn't take innodb_stats_method
variable while calculating n_diff_pfx for the n-prefix index columns.

Solution:

InnoDB consider all nulls as different value when innodb_stats_method is set to NULLS_UNEQUAL and NULLS_IGNORED.

Release Notes

InnoDB consider innodb_stats_method while calculating persistent statistics

How can this PR be tested?

./mtr innodb.innodb_stats_method

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

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[dr-m]

The commit message mentions that a value is set to one AND another. It should clearly be OR.

I think that the commit message needs to emphasize that the contents of the statistics depends on the value of the parameter when the statistics were last recalculated. We have an informational column in the statistics tables. Could the used value of innodb_stats_method be written there?

[dr-m]

Instead of checking the value of the global variable in each iteration, I think that it would be better to evaluate this condition only once and pass it in a bool parameter to the affected functions.

[Thirunarayanan]

This issue is being fixed in 10.11 branch. Check #4204