zabbix=# select datname, blks_hit * 100.0 / (blks_read + blks_hit) AS cache_hit, stats_reset from pg_stat_database where datname = 'zabbix';
datname | cache_hit | stats_reset
---------+---------------------+-------------------------------
zabbix | 78.4450092005849089 | 2020-07-26 18:50:13.592914+09
(1 row)
zabbix=# select pg_stat_reset();
pg_stat_reset
---------------
(1 row)
zabbix=# select datname, blks_hit * 100.0 / (blks_read + blks_hit) AS cache_hit, stats_reset from pg_stat_database where datname = 'zabbix';
datname | cache_hit | stats_reset
---------+---------------------+-------------------------------
zabbix | 99.8402555910543131 | 2020-08-17 08:32:21.216764+09
(1 row)