MDEV-35889 set information_schema.system_variables NUMERIC_MIN_VALUE for the innodb_buffer_pool_size system variable based on innodb_page_size

[grooverdan]

• The Jira issue number for this PR is: MDEV-35889

Description

reasons for a new function plugin_opt_set_limits_by_name:

• plugin_opt_set_limits looks like it will do the job, however struct my_option * never gets exposed to the plugin to use. Also to preserve the plugin_opt_set_limits if somehow an plugin did use the interface.
• exposing intern_find_sys_var to a plugin looks like a layering violation, but otherwise including sql/sys_vars_shared.h does a compile error on THD (for other functions there).

The innodb_buffer_pool_size is dependent on the innodb_page_size. While the minimum is enforced for resizing the minimum isn't exposed by the information_schema.system_variables table.

This creates a plugin function plugin_opt_set_limits_by_name that allows plugins to adjust the limits of their system variables during plugin initialization.

Release Notes

information.system_variables no includes the right NUMBERIC_MIN_VALUE for innodb_buffer_pool_size, regardless of which innodb_page_size is used.

How can this PR be tested?

mtr case included

If the changes are not amenable to automated testing, please explain why not and carefully describe how to test manually.

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.

[vuvova]

I think it went the wrong way. Instead of adding a function for plugin to call to adjust the limits, I'd add an assert into OPTION_SET_LIMITS that max, min, and default values are divisible by the block size. And the same into Sys_var_integer::Sys_var_integer. Also, other asserts from Sys_var_integer could make sense in OPTION_SET_LIMITS too (like min < max)

[grooverdan]

I think it went the wrong way. Instead of adding a function for plugin to call to adjust the limits, I'd add an assert into OPTION_SET_LIMITS that max, min, and default values are divisible by the block size. And the same into Sys_var_integer::Sys_var_integer. Also, other asserts from Sys_var_integer could make sense in OPTION_SET_LIMITS too (like min < max)

I don't follow how assertions are solving a problem. I'm not solving MDEV-35890 here. The innodb buffer pool size is dependent on the page size, set in innodb_init_params, but Sys_vars are initialized before this is called.

Another deeper change possibility that I think is more correct is changing the sys_var min/max/default to pointers and point them to the st_mysql_sys_var values rather than copying them. This saves doing a plugin_opt_set_limits call, but I haven't looked all the way though here.

And missed including test result change. opps.

[vuvova]

Variable metadata (for a integer sysvar) include min and max values and a block size. It's reasonable to expect these values to be consistent with each other. min should be less than max. both min and max should be divisible by block size.

Asserts would ensure that variable metadata is internally consistent.