MDEV-37619 The forced use of THD accessors hurts InnoDB performance

[dr-m]

• The Jira issue number for this PR is: MDEV-37619

Description

Let InnoDB access some data members of THD directly, instead of invoking non-inline accessor functions. Note: my_thread_id will be used instead of the potentially narrower ulong data type.

Also, let us remove some functions from sql_class.cc that were only being used by InnoDB or RocksDB, for no reason. RocksDB always had access to the internals of THD.

Release Notes

The performance of InnoDB was slightly improved.

How can this PR be tested?

The performance impact has been tested in MDEV-37152 as part of #4252.

The modified code should be well exercised by the default regression tests. No change in behaviour is expected.

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.

I believe that this would benefit the 10.6 branch as well, but there are several other performance fixes that were already omitted from the 10.6 branch.

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]

For the record, a cmake -DPLUGIN_INNOBASE=DYNAMIC build would fail both before and after these changes. Setting cmake -DWITH_WSREP=OFF would fix most of that, but some problems that were introduced in #3022 and a2d3770. Below are some compiler messages for f609dbd for cmake -DPLUGIN_INNOBASE=DYNAMIC -DWITH_WSREP=OFF:

storage/innobase/handler/ha_innodb.cc: In function ‘void innodb_transaction_abort(THD*, bool, dberr_t)’:
storage/innobase/handler/ha_innodb.cc:2073:31: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
 2073 |     if (thd_log_warnings(thd) >= 4)
storage/innobase/handler/ha_innodb.cc: In member function ‘virtual int ha_innobase::check(THD*, HA_CHECK_OPT*)’:
storage/innobase/handler/ha_innodb.cc:15316:17: error: ‘print_check_msg’ was not declared in this scope
15316 |                 print_check_msg(thd, table->s->db.str, table->s->table_name.str,
      |                 ^~~~~~~~~~~~~~~

The first error would actually be fixed by this pull request; thd->variables.log_warnings appears to be fine.