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In commit 99bd22605938c42d876194f2ec75b32e658f00f5 (MDEV-31558) we wrongly thought that there would be minimal overhead for accessing a thread-local variable mariadb_stats. It turns out that in C++11, each access to an extern thread_local variable requires conditionally invoking an initialization function. In fact, the initializer expression of mariadb_stats is dynamic, and those calls were actually unavoidable. In C++20, one could declare constinit thread_local variables, but the address of a thread_local variable (&mariadb_dummy_stats) is not a compile-time constant. We did not want to declare mariadb_dummy_stats without thread_local, because then the dummy accesses could lead to cache line contention between threads. mariadb_stats: Declare as __thread or __declspec(thread) so that there will be no dynamic initialization, but zero-initialization. mariadb_dummy_stats: Remove. It is a lesser evil to let the environment perform zero-initialization and check if !mariadb_stats. Reviewed by: Sergei Petrunia |
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| archive | ||
| blackhole | ||
| columnstore | ||
| connect | ||
| csv | ||
| example | ||
| federated | ||
| federatedx | ||
| heap | ||
| innobase | ||
| maria | ||
| mroonga | ||
| myisam | ||
| myisammrg | ||
| oqgraph | ||
| perfschema | ||
| rocksdb | ||
| sequence | ||
| sphinx | ||
| spider | ||
| test_sql_discovery | ||