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31 строка
1.8 KiB
Plaintext
31 строка
1.8 KiB
Plaintext
2023
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Tenzor - Backend School p4 - Query Analysis p2 10:00 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! 27:48 - if counts of planned and actual record does not near the same, most probably statistics is obsolete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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