Re: xmin and very high number of concurrent transactions

On Wed, Mar 13, 2019 at 9:50 AM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> wrote:
>
> Vijaykumar Jain wrote:
> > I was asked this question in one of my demos, and it was interesting one.
> >
> > we update xmin for new inserts with the current txid.
> > now in a very high concurrent scenario where there are more than 2000
> > concurrent users trying to insert new data,
> > will updating xmin value be a bottleneck?
> >
> > i know we should use pooling solutions to reduce concurrent
> > connections but given we have enough resources to take care of
> > spawning a new process for a new connection,
>
> You can read the function GetNewTransactionId in
> src/backend/access/transam/varsup.c for details.
>
> Transaction ID creation is serialized with a "light-weight lock",
> so it could potentially be a bottleneck.

Also I think that GetSnapshotData() would be the major bottleneck way
before GetNewTransactionId() becomes problematic. Especially with
such a high number of active backends.