Re: suboverflowed subtransactions concurrency performance optimize

On Fri, 3 Dec 2021 at 01:27, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:

> > On review, I think it is also possible that we update subtrans ONLY if
> > someone uses >PGPROC_MAX_CACHED_SUBXIDS.
> > This would make subtrans much smaller and avoid one-entry-per-page
> > which is a major source of cacheing.
> > This would means some light changes in GetSnapshotData().
> > Let me know if that seems interesting also?
>
> Do you mean to say avoid setting the sub-transactions parent if the
> number of sun-transactions is not crossing PGPROC_MAX_CACHED_SUBXIDS?
> But the TransactionIdDidCommit(), might need to fetch the parent if
> the transaction status is TRANSACTION_STATUS_SUB_COMMITTED, so how
> would we handle that?

TRANSACTION_STATUS_SUB_COMMITTED is set as a transient state during
final commit.
In that case, the top-level xid is still in procarray when nsubxids <
PGPROC_MAX_CACHED_SUBXIDS
so we need not consult pg_subtrans in that case, see step 4 of
TransactionIdIsInProgress()

--
Simon Riggs http://www.EnterpriseDB.com/