notes/db/sql/postgres/feature/performance/planner/statistics.txt

https://www.postgresql.org/docs/current/sql-createstatistics.html
    !!! alter table ... alter column ... set statistics [0..10000] -- columns of hystogram (max 10000 per column)

https://www.postgresql.org/docs/current/planner-stats.html
https://www.postgresql.org/docs/current/multivariate-statistics-examples.html

CREATE EXTENSION pgstattuple;
SELECT * FROM pgstattuple('table-name') \gx
-[ RECORD 1 ]------+--------
table_len          | 4427680
tuple_count        | 100000
tuple_len          | 3368895
tuple_percent      | 76.61
dead_tuple_count   | 0
dead_tuple_len     | 0
dead_tuple_percent | 0
free_space         | 16552
free_percent       | 0.37

tuple_percent - percent of useful info
free_percent - .. of free (old row versions and free space)
dead_tuple_count - quality of autovacuum

SELECT relname, n_live_tup, n_dead_tup
FROM pg_stat_user_tables/pg_stat_all_tables;

SELECT
    relname AS "table",
    n_live_tup AS live_rows,
    n_dead_tup AS dead_rows,
    ROUND((n_dead_tup::float8 / NULLIF(n_live_tup + n_dead_tup, 0)) * 100, 2) AS dead_proc
FROM
    pg_stat_user_tables
WHERE
    n_live_tup + n_dead_tup > 0
ORDER BY
    dead_proc DESC;

SELECT relname, last_autovacuum, last_autoanalyze
FROM pg_stat_user_tables
WHERE relname="<table-name>";