po 2. 5. 2022 v 16:02 odesílatel Pavel Stehule <pavel.steh...@gmail.com> napsal:
> > > po 2. 5. 2022 v 15:28 odesílatel Matthias van de Meent < > boekewurm+postg...@gmail.com> napsal: > >> On Mon, 2 May 2022 at 11:00, Pavel Stehule <pavel.steh...@gmail.com> >> wrote: >> > >> > Hi >> > >> > I found a query that is significantly slower with more memory >> >> Which PostgreSQL version did you use? Did you enable assert checking? >> Do you have an example database setup to work with? >> >> > plan 2 >> > QUERY PLAN >> > ---------------- >> > Nested Loop Anti Join (cost=46.53..2914.58 rows=1 width=16) (actual >> time=18.306..23.065 rows=32 loops=1) >> > ... >> > Execution Time: 451.161 ms >> >> Truly strange; especially the 418ms difference between execution time >> and the root node's "actual time". I haven't really seen such >> differences happen, except when concurrent locks were held at the >> table / index level. >> >> > plan 1 - fast https://explain.depesz.com/s/XM1f >> > >> > plan 2 - slow https://explain.depesz.com/s/2rBw >> > >> > Strange - the time of last row is +/- same, but execution time is 10x >> worse >> >> The only difference between the two plans that I see is that plan 1 >> doesn't use memoization, whereas plan 2 does use 2 memoize plan nodes >> (one of 66 misses; one of 342 misses). The only "expensive" operation >> that I see in memoize nodes is the check for memory size in >> assert-enabled builds; and that should have very low overhead >> considering that the size of the memoized data is only 8kB and 25kB >> respectively. >> > > This is PostgreSQL 14 used in production environment > > (2022-05-02 15:37:29) prd_aukro=# show debug_assertions ; > ┌──────────────────┐ > │ debug_assertions │ > ├──────────────────┤ > │ off │ > └──────────────────┘ > (1 řádka) > > Čas: 0,295 ms > (2022-05-02 15:37:35) prd_aukro=# select version(); > > ┌────────────────────────────────────────────────────────────────────────────────────────────────────────┐ > │ version > │ > > ├────────────────────────────────────────────────────────────────────────────────────────────────────────┤ > │ PostgreSQL 14.2 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 > 20210514 (Red Hat 8.5.0-4), 64-bit │ > > └────────────────────────────────────────────────────────────────────────────────────────────────────────┘ > (1 řádka) > Čas: 0,629 ms > > there is just shared buffers changed to 32GB and work_mem to 70MB. > Unfortunately - it is in production environment with customer data, so I > cannot to play too much > > This is perf of slow > > 25,94% postmaster [kernel.kallsyms] [k] clear_page_erms > 11,06% postmaster [kernel.kallsyms] [k] page_fault > 5,51% postmaster [kernel.kallsyms] [k] prepare_exit_to_usermode > 5,18% postmaster [kernel.kallsyms] [k] __list_del_entry_valid > 5,15% postmaster libc-2.28.so [.] __memset_avx2_erms > 3,99% postmaster [kernel.kallsyms] [k] unmap_page_range > 3,07% postmaster postgres [.] hash_search_with_hash_value > 2,73% postmaster [kernel.kallsyms] [k] cgroup_throttle_swaprate > 2,49% postmaster postgres [.] heap_page_prune_opt > 1,92% postmaster [kernel.kallsyms] [k] try_charge > 1,85% postmaster [kernel.kallsyms] [k] > swapgs_restore_regs_and_return_to_usermode > 1,82% postmaster [kernel.kallsyms] [k] error_entry > 1,73% postmaster postgres [.] _bt_checkkeys > 1,48% postmaster [kernel.kallsyms] [k] free_pcppages_bulk > 1,35% postmaster [kernel.kallsyms] [k] get_page_from_freelist > 1,20% postmaster [kernel.kallsyms] [k] __pagevec_lru_add_fn > 1,08% postmaster [kernel.kallsyms] [k] > percpu_ref_put_many.constprop.84 > 1,08% postmaster postgres [.] 0x00000000003c1be6 > 1,06% postmaster [kernel.kallsyms] [k] get_mem_cgroup_from_mm.part.49 > 0,86% postmaster [kernel.kallsyms] [k] __handle_mm_fault > 0,79% postmaster [kernel.kallsyms] [k] mem_cgroup_charge > 0,70% postmaster [kernel.kallsyms] [k] release_pages > 0,61% postmaster postgres [.] _bt_checkpage > 0,61% postmaster [kernel.kallsyms] [k] free_pages_and_swap_cache > 0,60% postmaster [kernel.kallsyms] [k] handle_mm_fault > 0,57% postmaster postgres [.] tbm_iterate > 0,56% postmaster [kernel.kallsyms] [k] __count_memcg_events.part.70 > 0,55% postmaster [kernel.kallsyms] [k] __mod_memcg_lruvec_state > 0,52% postmaster postgres [.] 0x000000000015f6e5 > 0,50% postmaster [kernel.kallsyms] [k] prep_new_page > 0,49% postmaster [kernel.kallsyms] [k] __do_page_fault > 0,46% postmaster [kernel.kallsyms] [k] _raw_spin_lock > 0,44% postmaster [kernel.kallsyms] [k] do_anonymous_page > > This is fast > > 21,13% postmaster postgres [.] hash_search_with_hash_value > 15,33% postmaster postgres [.] heap_page_prune_opt > 10,22% postmaster libc-2.28.so [.] __memset_avx2_erms > 10,00% postmaster postgres [.] _bt_checkkeys > 6,23% postmaster postgres [.] 0x00000000003c1be6 > 4,94% postmaster postgres [.] _bt_checkpage > 2,85% postmaster postgres [.] tbm_iterate > 2,31% postmaster postgres [.] nocache_index_getattr > 2,13% postmaster postgres [.] pg_qsort > 1,58% postmaster postgres [.] heap_hot_search_buffer > 1,58% postmaster postgres [.] FunctionCall2Coll > 1,58% postmaster postgres [.] 0x000000000015f6e5 > 1,17% postmaster postgres [.] LWLockRelease > 0,85% postmaster libc-2.28.so [.] __memcmp_avx2_movbe > 0,64% postmaster postgres [.] 0x00000000003e4233 > 0,54% postmaster postgres [.] hash_bytes > 0,53% postmaster postgres [.] 0x0000000000306fbb > 0,53% postmaster postgres [.] LWLockAcquire > 0,42% postmaster postgres [.] 0x00000000003c1c6f > 0,42% postmaster postgres [.] _bt_compare > > It looks so memoization allocate lot of memory - maybe there are some temporal memory leak Performance counter stats for process id '4004464': 84,26 msec task-clock # 0,012 CPUs utilized 3 context-switches # 0,036 K/sec 0 cpu-migrations # 0,000 K/sec 19 page-faults # 0,225 K/sec 0 cycles # 0,000 GHz 106 873 995 instructions 20 225 431 branches # 240,026 M/sec 348 834 branch-misses # 1,72% of all branches 7,106142051 seconds time elapsed Performance counter stats for process id '4004464': 1 116,97 msec task-clock # 0,214 CPUs utilized 4 context-switches # 0,004 K/sec 0 cpu-migrations # 0,000 K/sec 99 349 page-faults # 0,089 M/sec 0 cycles # 0,000 GHz 478 842 411 instructions 89 495 015 branches # 80,123 M/sec 1 014 763 branch-misses # 1,13% of all branches 5,221116331 seconds time elapsed Regards Pavel > > > > Regards > > Pavel > >
