We need to log aborted autovacuums

Hackers,

I've been trying to diagnose in a production database why certain tables
never get autovacuumed despite having a substantial % of updates. The
obvious reason is locks blocking autovacuum from vacuuming the table ...
but the trick is we don't log such blocking behavior, at all. This
means that there is no possible way for a user to figure out *why* his
tables aren't getting autovacuumed.

And yes, this is a common problem. A quick survey on IRC found 3 active
users on channel (out of 20 or so) who'd encountered it. The current
case I'm looking at is a table with over 70% bloat which hasn't been
autovacuumed since the database was upgraded a month ago.

What I'd like to do is add some logging code to autovacuum.c so that if
log_autovacuum is any value other than -1, failure to vacuum due to
locks gets logged. Does this make sense?

And does anyone have suggestions on how users can diagnose this on older
versions?

--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com