Feeds as cache invalidation mechanism

One really cool use of feeds we’ve realized is that it gives a very efficient mechanism for application code to load the most recent versions of a table into memory. The basic idea is:

1. Set it up as a usual feed published table with an appropriate index on feed_sync_id.
2. Either alongside or within the cache, represent the latest loaded feed_sync_id.
3. Set up a cronjob/etc that reads the latest feed_sync_id and compares it to the cache’s feed_sync_id.
4. If they differ, reload the cache.
5. Ensure that all changes set feed_sync_id to null!

This works really well because the feed_sync_id in the database only gets updated on changes, so the reload cronjob mostly is a no-op. This means we can reload very frequently!