On Mon, Sep 16, 2019 at 10:29:18PM +0300, Konstantin Knizhnik wrote:
On 16.09.2019 19:54, Alexey Kondratov wrote:
On 30.08.2019 18:59, Konstantin Knizhnik wrote:
I think that instead of defining savepoints it is simpler and more
efficient to use
BeginInternalSubTransaction +
ReleaseCurrentSubTransaction/RollbackAndReleaseCurrentSubTransaction
as it is done in PL/pgSQL (pl_exec.c).
Not sure if it can pr
Both BeginInternalSubTransaction and DefineSavepoint use
PushTransaction() internally for a normal subtransaction start. So
they seems to be identical from the performance perspective, which
is also stated in the comment section:
Yes, definitely them are using the same mechanism and most likely
provides similar performance.
But BeginInternalSubTransaction does not require to generate some
savepoint name which seems to be redundant in this case.
Anyway, I've performed a profiling of my apply worker (flamegraph is
attached) and it spends the vast amount of time (>90%) applying
changes. So the problem is not in the savepoints their-self, but in
the fact that we first apply all changes and then abort all the
work. Not sure, that it is possible to do something in this case.
Looks like the only way to increase apply speed is to do it in
parallel: make it possible to concurrently execute non-conflicting
transactions.
True, although it seems like a massive can of worms to me. I'm not aware
a way to identify non-conflicting transactions in advance, so it would
have to be implemented as optimistic apply, with a detection and
recovery from conflicts.
I'm not against doing that, and I'm willing to spend some time on revies
etc. but it seems like a completely separate effort.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
