Optimize Postgres Containers for Testing [RE#15]

Recently, I had this task of transferring our tests from using in-memory SQLite instances to Postgres containers. It seemed a like a pretty straightforward set of changes, until I realized it’s not. I had to fix some random unexpected issues down the road. But the biggest (and to be fair, the most expected) one was the poor performance of the tests after fully migrating to Postgres.

Long story short, after some Internet search and reading documentations, I ended up getting a good performance (very close to what we had with SQLite) using the docker-compose.yaml configuration below:

services:
  postgres:
    image: postgres
    restart: always
    ports:
      - 5432:5432
    # Remove the `tmpfs` key below, either:
    # - If you don't want to lose the data after the container stops/restarts.
    # - If the data can be too large for the memory.
    tmpfs:
      - /var/lib/postgresql/data
    # Since it's mainly used for testing purposes, it's okay to set fsync=off for
    # improved performance.
    command: -c fsync=off -c full_page_writes=off

The key points here are:

• Using tmpfs : With tmpfs mounts, you can utilize memory (RAM) as the underlying filesystem storage for specific paths. Here I’ve used it to store Postgres data. This, of course, means there’s no real persistence in-place, therefore you will lose the data if the container stops/restarts. Also, you have to be careful with the size of the data, in case it could get close to your memory limits.

• Applying -c fsync=off -c full_page_writes=off : If you don’t disable the fsync option, Postgres makes sure that updates are physically written to disk, which could be a great performance hit. As of official documentations, if you turn fsync off, you should also consider disabling full_page_writes.

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