Re: [PERFORM] Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit - Mailing list pgsql-patches

"Pavan Deolasee" <pavan.deolasee@gmail.com> writes:
> On Wed, Mar 12, 2008 at 9:27 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> and it would have problems with a slow transaction
>> generating a sparse set of subtransaction XIDs.

> I agree thats the worst case. But is that common ? Thats what I
> was thinking when I proposed the alternate solution. I thought that can
> happen only if most of the subtransactions abort, which again I thought
> is not a normal case.

No, I was thinking of the case where other sessions are chewing up XIDs
while the lots-of-subtransactions transaction runs.  If it's slow
enough, there could be very large gaps between the XIDs it acquires for
its subtransactions.  So you'd have a situation where the exact same
transaction processing might or might not run out of memory depending
on what else happened meanwhile.  Not a very pleasant property.

            regards, tom lane