Re: Reasons for choosing one execution plan over another?

Hi all,

I have a number of Postgres 9.2.4 databases with the same schema but with
slightly different contents, running on small servers that are basically
alike (8-16 GB ram).

When I run the same query on these databases it results in one of two
different execution plans where one is much faster (appx. 50 times) than
the other. Each database always gives the same plan, and vacuuming,
updating statistics and reindexing doesn't seem to make any difference.

Clearly the fast plan is preferred, but I haven't been able to identify
any pattern (table sizes, tuning etc.) in why one plan is chosen over the
other, so is there any way I can make Postgres tell me why it chooses to
plan the way it does?