| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Konstantin Knizhnik <knizhnik(at)garret(dot)ru> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Race condition in TransactionIdIsInProgress |
| Date: | 2022-02-10 20:21:27 |
| Message-ID: | CA+TgmoaTUg8B-hfj5N212yyb2GMxr2-4sZ=x_tKfui551NxOTw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Feb 10, 2022 at 11:46 AM Konstantin Knizhnik <knizhnik(at)garret(dot)ru> wrote:
> Postgres first records state transaction in CLOG, then removes
> transaction from procarray and finally releases locks.
> But it can happen that transaction is marked as committed in CLOG,
> XMAX_COMMITTED bit is set in modified tuple but
> TransactionIdIsInProgress still returns true. As a result "t_xmin %u is
> uncommitted in tuple (%u,%u) to be updated in table"
> error is reported.
This is exactly why the HeapTupleSatisfiesFOO() functions all test
TransactionIdIsInProgress() first and TransactionIdDidCommit() only if
it returns false. I don't think it's really legal to test
TransactionIdDidCommit() without checking TransactionIdIsInProgress()
first. And I bet that's exactly what this code is doing...
--
Robert Haas
EDB: http://www.enterprisedb.com
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