POSTGRES: Disk bound IO - possible to keep table in memory?

Question

I'm a relative Postgres newbie, though have some basic experience with MSSQL.

I have a table on PostgreSQL (PostGIS, it's spatial) that contains about 10,000,000 polygons. The machine it's sitting on has 64gb RAM, 16 cores and a 1TB spinning HDD. This is only of the only tables in the database at the moment. Because access to the table is infrequent (perhaps once every few hours) I'm noticing that the table will not stay located in RAM, as I would expect with MSSQL. Instead, the table seems to be released from memory and sit on disc in an active state. This is leading to 100% HDD utilization for 15+ minutes when I want to query / join / interrogate / etc. When the table seemingly appears to be in memory subsequent operations are notably faster (seconds rather than minutes).

Is there a way to ask Postgres to keep a certain table in memory, or have the scheduler / whatever bits of postgres that perform the smarts keep the table in ram, rather than letting it go to disk then having to recall it into memory when required?

I have spatial indexes (and a couple of other columns that often require filtering / sorting indexed), so when being called from memory it's quite fast.

This same issue also seems to massively affect JOINS, because they too require the table to be read first. This is a separate issue for me, but seemingly affected by the same root problem. Disk IO bound.

My DB settings are as such - so generally I'm not inhibited by available memory / ram, so far as I can tell.

Edit: Table is 26gb

Postgres 13.2 with PostGIS 3.1.1

 max_connections = '20';
 shared_buffers = '8GB';
 effective_cache_size = '24GB';
 maintenance_work_mem = '2047MB';
 checkpoint_completion_target = '0.9';
 wal_buffers = '16MB';
 default_statistics_target = '500';
 random_page_cost = '4';
 work_mem = '26214kB';
 min_wal_size = '4GB';
 max_wal_size = '16GB';
 max_worker_processes = '16';
 max_parallel_workers_per_gather = '8';
 max_parallel_workers = '16';
 max_parallel_maintenance_workers = '4';

Answer 1

You didn't say how large the table is.

Data is never evicted from shared buffers just out of boredom. Only to make room for other things, or because they became invalid (table dropped or truncated, etc.). So if you make shared buffers large enough and read the whole table in with pg_prewarm, it will stay there until displaced. (There is a mechanism for sequential scans of large tables that will preferentially evict data it just read to make room for more data from the same table, but pg_prewarm is not subject to that). If the entire database fits in shared buffers, it will all be retained indefinitely.

Stock postgresql offers no other way to pin a table or list of tables into memory.