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56 строки
2.0 KiB
Plaintext
56 строки
2.0 KiB
Plaintext
https://www.postgresql.org/docs/current/sql-createstatistics.html
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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/planner-stats.html
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https://www.postgresql.org/docs/current/multivariate-statistics-examples.html
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2023
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Otus - Anton Zolotov - Statistics usage for Query Optimization 1:20:00 of 1:55:27
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https://www.youtube.com/watch?v=yNAbEtnFikI
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! 14:00 - create table ... with(autovacuum_enabled=false);
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! 19:00 - select reltuples, relpages from pg_class where relname='<our-table>';
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! -1 0
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! 26:00 - pg_statistics/pg_stats view
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! null_frac, n_distinct -- negative/positive values - are real-num/fraction
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! 28:00 - while analyze, table is checked not fully (default_statistics_target (100) * 300 = 300 000 is statistically good number of rows)
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! clustered idx - data is ordered
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! correlation - data is ordered asc, 0 - not orered, -1 - desc
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! most_common_vals - array (of 100)
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! most_common_freqs - array as well (of 100)
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CREATE EXTENSION pgstattuple;
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SELECT * FROM pgstattuple('table-name') \gx
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-[ RECORD 1 ]------+--------
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table_len | 4427680
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tuple_count | 100000
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tuple_len | 3368895
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tuple_percent | 76.61
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dead_tuple_count | 0
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dead_tuple_len | 0
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dead_tuple_percent | 0
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free_space | 16552
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free_percent | 0.37
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tuple_percent - percent of useful info
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free_percent - .. of free (old row versions and free space)
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dead_tuple_count - quality of autovacuum
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SELECT relname, n_live_tup, n_dead_tup
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FROM pg_stat_user_tables/pg_stat_all_tables;
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SELECT
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relname AS "table",
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n_live_tup AS live_rows,
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n_dead_tup AS dead_rows,
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ROUND((n_dead_tup::float8 / NULLIF(n_live_tup + n_dead_tup, 0)) * 100, 2) AS dead_proc
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FROM
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pg_stat_user_tables
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WHERE
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n_live_tup + n_dead_tup > 0
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ORDER BY
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dead_proc DESC;
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SELECT relname, last_autovacuum, last_autoanalyze
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FROM pg_stat_user_tables
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WHERE relname="<table-name>";
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