Postgres hit ratio: should big history tables be removed from the production database?



  • A database has these cache hit ratios:

    table A: 0.006
    table B: 0.955
    table C: 0.023
    

    Tables A and C are history tables. No relationship, large content and no need of fast queries, only few read requests. I looked for a feature to tell Postgres to ignore cache for these tables, in vain.

    Are things as easy as if tables A and C are removed from the database, it will automatically increase the cache hit ratio for table B? (assuming the same amount of data)



  • PostgreSQL always caches pages it reads, there is no way to avoid that. Dropping tables A and C may improve the cache hit ratio for table B, but not by much, because there is not much room for improvement. Perhaps there are some parts of table B that are not in constant use.

    It seems to me that PostgreSQL is already doing what you want it to do: pages from tables A and C drop out of the cache, and pages from B mostly stay in cache.




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