I have read https://www.postgresql.org/docs/current/monitoring-stats.html#MONITORING-PG-STATIO-ALL-TABLES-VIEW
But it does not clarify whether this data is over the whole history of the DB (unless you reset the stats counters). Or whether it is just for recent data.
I am seeing a low cache-hit ratio on one of my tables, but I recently added an index to it. I'm not sure if it is low from all the pre-index usage, or if it is still low, even with the index.