Pavel Stehule писал 2021-05-07 21:45:
Samples: 119K of event 'cycles', 4000 Hz, Event count (approx.): Overhead Shared Object Symbol 79.20% postgres [.] cache_reduce_memory 1.94% [kernel] [k] native_write_msr_safe 1.63% [kernel] [k] update_cfs_shares 1.00% [kernel] [k] trigger_load_balance 0.97% [kernel] [k] timerqueue_add 0.51% [kernel] [k] task_tick_fair 0.51% [kernel] [k] task_cputime 0.50% [kernel] [k] perf_event_task_tick 0.50% [kernel] [k] update_curr 0.49% [kernel] [k] hrtimer_active Regards Pavel
It is strange to see cache_reduce_memory itself consumes a lot of CPU. It doesn't contain CPU hungry code. It calls prepare_probe_slot, that calls some tuple forming. Then it calls resultcache_lookup that may call to ResultCacheHash_hash and ResultCacheHash_equal. And finally it calls remove_cache_entry. I suppose remove_cache_entry should consume most of CPU time since it does deallocations. And if you compile with --enable-cassert, then remove_cache_entry iterates through whole cache hashtable, therefore it reaches quadratic complexity easily (or more correct M*N, where M - size of a table, N - eviction count). regards, Yura Sokolov
