On Fri, May 13, 2022 at 9:18 PM Bruce Momjian <br...@momjian.us> wrote: > > On Fri, May 13, 2022 at 08:24:53AM +0530, Amit Kapila wrote: > > On Fri, May 13, 2022 at 6:02 AM Euler Taveira <eu...@eulerto.com> wrote: > > > > > > On Thu, May 12, 2022, at 11:22 AM, Bruce Momjian wrote: > > > > > > On Thu, May 12, 2022 at 11:12:54AM -0300, Euler Taveira wrote: > > > OB> On Thu, May 12, 2022, at 11:03 AM, Bruce Momjian wrote: > > > > > > > > I looked at that but thought that everyone would already assume we > > > > skipped replication of empty transactions, and I didn't see much > > > > impact > > > > for the user, so I didn't include it. > > > > > > > > It certainly has an impact on heavy workloads that replicate tables > > > > with few > > > > modifications. It receives a high traffic of 'begin' and 'commit' > > > > messages that > > > > the previous Postgres versions have to handle (discard). I would > > > > classify it as > > > > a performance improvement for logical replication. Don't have a strong > > > > opinion > > > > if it should be mentioned or not. > > > > > > Oh, so your point is that a transaction that only has SELECT would > > > previously send an empty transaction? I thought this was only for apps > > > that create literal empty transactions, which seem rare. > > > > > > No. It should be a write transaction. If you have a replication setup that > > > publish only table foo (that isn't modified often) and most of your > > > workload does not contain table foo, Postgres sends 'begin' and 'commit' > > > messages to subscriber even if there is no change to replicate. > > > > > > > It reduces network traffic and improves performance by 3-14% on simple > > tests [1] like the one shown by Euler. I see a value in adding this as > > for the workloads where it hits, it seems more than 99% of network > > traffic [2] is due to these empty messages. > > I see the point now --- new item: > > <!-- > Author: Amit Kapila <akap...@postgresql.org> > 2022-03-30 [d5a9d86d8] Skip empty transactions for logical > replication. > --> > > <listitem> > <para> > Prevent logical replication of empty transactions (Ajin Cherian, > Hou Zhijie, Euler Taveira) > </para> > > <para> > Previously, write transactions would send empty transactions to > subscribers if subscribed tables were not modified. > </para> > </listitem> >
Thanks! -- With Regards, Amit Kapila.
