In an attempt to address MDEV-34178, 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.
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Bug
Critical
I am setting this to Blocker to avoid a potentially severe performance regression in the upcoming quarterly releases. I will address this in about a month, after returning from vacation.