Thread: Can autovacuum result in large surges in WAL files

I have a Postgres 8.3 system that is configured to run autovacuum.  It triggered a vacuum analyze on multiple tables
andsince this started, we are getting large numbers of WAL files generated about every 15 minutes or so.  This same
vacuumappears to continuing to run.  Other database activity is at its usual levels.  Should a vacuum analyze lead to
largeamounts of data being written to WAL files?  We are seeing 10x the number WAL files that we would expect. 

Any ideas on the best approach to diagnose what is going on?

Todd Gugler <tgugler11@gmail.com> wrote:

> Should a vacuum analyze lead to large amounts of data being
> written to WAL files?

Yes, if it has to "freeze" the rows to prevent transaction
wraparound.

> We are seeing 10x the number WAL files that we would expect.
>
> Any ideas on the best approach to diagnose what is going on?

Is it vacuuming a table which was bulk loaded at some time in the
past?  If so, this can happen any time later (usually during busy
periods when many transactions numbers are being assigned).  To
prevent this in the future, run VACUUM FREEZE ANALYZE after any bulk
load.

There has been much talk about possible ways to avoid this behavior
by initially setting bulk loaded data to "frozen", but there are
technical problems which haven't been adequately addressed yet.

-Kevin