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73 строки
4.2 KiB
Plaintext
73 строки
4.2 KiB
Plaintext
2023
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Tenzor - Backend School p4 - Query Analysis p2 20:00 of 1:40:59
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https://www.youtube.com/watch?v=Rg7AAEso3z0
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! 5:00 - Custom Scan (<impl-method-name>)
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! Recheck Cond - ???
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! 7:00 - Beatmap Heap Scan
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! exact ... lossy - not enough mem for gen full bitmap map
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! 10:00 - Append + Unique (Sort Key:)
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Tenzor - Backend School p4 - Query Analysis p1 9:00 of 1:24:11
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https://www.youtube.com/watch?v=4g2CJv0jRk0
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! 3:00 - by default PG does not get hints regarding plans
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! 18:00 - explain(settings) select * from pg_class; -- to check current settings
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! https://www.postgresql.org/docs/current/runtime-config.html
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! 27:48 - if counts of planned and actual record does not near the same, most probably statistics is obsolete
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! https://www.postgresql.org/docs/current/planner-stats.html
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! https://www.postgresql.org/docs/current/runtime-config-autovacuum.html
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! 30:32 !!! not enough statistics
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! alter table ... alter column ... set statistics [0..10000] -- columns of hystogram (max 10000 per column)
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! https://www.postgresql.org/docs/current/sql-createstatistics.html
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! 39:00 - shared_buffers setting need to be increased if multiple clients get mostly the same data
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! 43:00 - set io_track_timings=on; explain analyze ...
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! 52:00 - ! rows removed by filter should be small
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! 58.00 - https://www.postgresql.org/docs/current/storage.html
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! 59.00 - https://www.postgresql.org/docs/current/storage-page-layout.html
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! TID Scan - the dumbiest one
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! Seq Scan - linear, dumb one
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! Index Scan - smart
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! Index Only Scan - smartest
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! 1:09:00 - if Heap Fetches quite large, we made worse by this idx, compare to just "Index Scan"
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! 1:13:00 - Foreign Scan - for tables on ext servers
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2021
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PGConf - Augustine - Deeper understanding of PG execution plan 35:00 of 47:55
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https://www.youtube.com/watch?v=Ls-uE1V31lE
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! 4:00 - debug_print_parse(boolean) - https://www.postgresql.org/docs/current/runtime-config-logging.html#GUC-DEBUG-PRINT-PARSE
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! https://postgrespro.ru/docs/postgrespro/current/runtime-config-logging#GUC-DEBUG-PRINT-PARSE
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! https://postgresqlco.nf/doc/en/param/debug_print_parse/
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! !!! and other interesting stuff for debug printing
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! 6:00 - pg_analyze_and_rewrite internal (c) func
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! https://patshaughnessy.net/2014/10/13/following-a-select-statement-through-postgres-internals
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! https://habr.com/ru/articles/304258/
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! https://medium.com/@divya.n/how-postgres-works-733bc5cf61a
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! https://github.com/melanieplageman/debugging_planner
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! 7:00 - set log_parser_stats=on
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! 11:00 - views are rules - pg_rewrite
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! https://www.postgresql.org/docs/current/rules.html
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! https://www.postgresql.org/docs/current/rules-views.html
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! 13:00 - Paths - internal DS, used for plans
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! 23:00 - Analyze
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! autovacuum gathers stats
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! pg_statistics, pg_stats,
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! default_statistics_target
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!!! https://postgrespro.ru/docs/postgresql/12/runtime-config-query#GUC-DEFAULT-STATISTICS-TARGET
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! https://postgresqlco.nf/doc/en/param/default_statistics_target/
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! https://postgrespro.ru/docs/postgrespro/current/catalog-pg-rewrite
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! https://www.postgresql.org/docs/current/catalog-pg-rewrite.html
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! https://dzone.com/articles/postgresql-rewrite-rules
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! https://habr.com/ru/companies/first/articles/656673/
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! 31:00 - seq_page_cost, random_page_cost, cpu_tuple_cost, cpu_index_tuple_cost
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! void cost_seqscan(Path *path, ...)
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! create tablespace tbs1 LOCATION '/var/local/../tbs1' with (seq_page_cost=1, random_page_cost=1.1, effective_io_concurrency=2);
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! 33:00 - select hystogram_bounds from pg_stats where ...
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! 35:00 - create statistics ...
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! 36:00 - parallel execution
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! parallel_setup_cost -> decides the plan
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! max_parallel_workers_per_gather -> number of workers in plan
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! table-level setting: set (parallel_workers = N)
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! max_parallel_workers -> decides execution
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! 37:00 - JIT
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! set jit=off;
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! https://www.tutorialdba.com/p/postgresql-query-flow.html
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! https://www.thatguyfromdelhi.com/2020/02/optimizations-in-group-by-vs-select.html
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