Re: Curious about dead rows.

On Nov 16, 2007 10:56 AM, Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info> wrote:
> On Wed, 2007-11-14 at 17:46 -0500, Tom Lane wrote:
> > Russell Smith <mr-russ(at)pws(dot)com(dot)au> writes:
> > > It is possible that analyze is not getting the number of dead rows right?
> >
> > Hah, I think you are on to something. ANALYZE is telling the truth
> > about how many "dead" rows it saw, but its notion of "dead" is "not good
> > according to SnapshotNow". Thus, rows inserted by a not-yet-committed
> > transaction would be counted as dead. So if these are background
> > auto-analyzes being done in parallel with inserting transactions that
> > run for awhile, seeing a few not-yet-committed rows would be
> > unsurprising.
> >
> > I wonder if that is worth fixing? I'm not especially concerned about
> > the cosmetic aspect of it, but if we mistakenly launch an autovacuum
> > on the strength of an inflated estimate of dead rows, that could be
> > costly.
>
> Sounds to me like that could result in autovacuum kicking off while
> doing large data loads. This sounds suspiciously like problem someone
> on -novice was having - tripping over a windows autovac bug while doing
> a data load
>
> http://archives.postgresql.org/pgsql-novice/2007-11/msg00025.php

I am almost 100% I've seen this behavior in the field...

merlin