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

2023
Otus - Anton Zolotov - Statistics usage for Query Optimization of 1:55:27
    https://www.youtube.com/watch?v=yNAbEtnFikI
    ! 14:00 - create table ... with(autovacuum_enabled=false);
    ! 19:00 - select reltuples, relpages from pg_class where relname='<our-table>';
    !         -1 0
    ! 26:00 - pg_statistics/pg_stats view
    !         null_frac, n_distinct   -- negative/positive values - are real-num/fraction
    ! 28:00 - while analyze, table is checked not fully (default_statistics_target (100) * 300 = 300 000 is statistically good number of rows)
    !         clustered idx - data is ordered
    !         correlation - data is ordered asc, 0 - not orered, -1 - desc
    !         most_common_vals - array (of 100)
    !         most_common_freqs - array as well (of 100)

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>";