.tip

If you want a cache and you already have Postgres, an UNLOGGED table skips the write-ahead log. Writes are close to memory speed, and the table is empty after a crash, which is exactly what a cache should be.

CREATE UNLOGGED TABLE cache (
  key text PRIMARY KEY, value jsonb NOT NULL, expires_at timestamptz NOT NULL
);
CREATE INDEX ON cache (expires_at);

A cleanup job deletes expired rows. Reads use the connection the request already has, so there is no second pool to run out of.