Re: suboverflowed subtransactions concurrency performance optimize

On Tue, Nov 30, 2021 at 5:49 PM Simon Riggs
<simon(dot)riggs(at)enterprisedb(dot)com> wrote:

> transam.c uses a single item cache to prevent thrashing from repeated
> lookups, which reduces problems with shared access to SLRUs.
> multitrans.c also has similar.
>
> I notice that subtrans. doesn't have this, but could easily do so.
> Patch attached, which seems separate to other attempts at tuning.

Yeah, this definitely makes sense.

> 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?

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com