Re: Query performance discontinuity

Mike,

> Given the estimated costs, PostgreSQL is doing the right things.
>
> However, in your case, it doesn't appear that the estimations are
> realistic.  Index scans are much cheaper than advertised.

Can I assume that you've run VACUUM FULL ANALYZE on the table, or
preferably the whole database?

>
> Try setting your random_page_cost lower (1.5 to 2 rather than 4).
> Bumping sortmem to 32 or 64MB (if plenty of ram is available) will
> help
> most situations.
>
> Might see the 'pg_autotune' project for assistance in picking good
> values.
>
> http://gborg.postgresql.org/project/pgautotune/projdisplay.php

Um.   I don't think we have anything to advertise yet, for pg_autotune.
  It's still very much an alpha, and the limits we set are pretty
arbitrary.

-Josh Berkus