| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Make HeapTupleSatisfiesMVCC more concurrent |
| Date: | 2015-08-21 14:52:20 |
| Message-ID: | CA+TgmoYGmD=noytwxuxuXYcaRNgEvsuJkAutKYBeLeSJbwEKeg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Aug 19, 2015 at 2:53 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> I think one case where the patch can impact is for aborted transactions.
> In TransactionIdIsInProgress(), we check for aborted transactions before
> consulting pg_subtrans whereas with patch it will consult pg_subtrans
> without aborted transaction check. Now it could be better to first check
> pg_subtrans if we found that the corresponding top transaction is
> in-progress as that will save extra pg_clog lookup, but I just mentioned
> because that is one difference that I could see with this patch.
>
> Another minor point is, I think we should modify function level comment
> for XidInMVCCSnapshot() where it says that this applies to known-
> committed XIDs which will no longer be true after this patch.
But only if the snapshot has overflowed, right? That should affect
only a small minority of cases.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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