The question was asked relatively recently on irc. And it proved to be non-trivial.
Surely, if you want to have one row per category (one address per user), it's trivial – add user_id column to addresses, make it unique, and we're done. But what if we want to allow five addresses? Or five thousands?
Continue reading How to limit rows to at most N per category
On 20th of December, Robert Haas committed patch:
pg_prewarm, a contrib module for prewarming relationd data.
Patch by me. Review by Álvaro Herrera, Amit Kapila, Jeff Janes,
Gurjeet Singh, and others.
Continue reading Waiting for 9.4 – pg_prewarm, a contrib module for prewarming relationd data.