MDEV-34431 More fine grained control of spin loops could be useful

[dr-m]

trafficstars

• [x] The Jira issue number for this PR is: MDEV-34431

Description

In 5b26a07698b92f58e5d1f55c7929b0e25d1a586b (#3317) I enabled spin loops on dict_index_t::lock. This helps in some workloads and causes performance degradation in others, especially when there are large numbers of concurrent connections.

It could make sense to enable spin loops on a case-by-case basis, or to introduce a configuration parameter for choosing when index tree latch acquisition should include spin loops.

Release Notes

TBD

How can this PR be tested?

I would like to see stack traces of the most popular spin loops for index_lock in a workload where 5b26a07698b92f58e5d1f55c7929b0e25d1a586b causes a regression. Maybe we can selectively disable spin loops in some fo those cases.

If there is no such low-hanging fruit, then this should be revised further with a runtime parameter to enable or disable spin loops for index_lock.

Basing the PR against the correct MariaDB version

• [ ] This is a new feature and the PR is based against the latest MariaDB development branch.
• [x] 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

• [x] 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.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}