| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Gregory Stark <stark(at)enterprisedb(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Neil Conway <neilc(at)samurai(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: advancing snapshot's xmin |
| Date: | 2008-03-28 14:26:34 |
| Message-ID: | 20080328142634.GM7464@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Fri, 2008-03-28 at 10:35 -0300, Alvaro Herrera wrote:
>
> > The problem is that we always consider every transaction's PGPROC->xid
> > in calculating MyProc->xmin. So if you have a long running
> > transaction, it doesn't matter how far beyond the snapshots are -- the
> > value returned by GetOldestXmin will always be at most the old
> > transaction's Xid. Even if that transaction cannot see the old rows
> > because all of its snapshots are way in the future.
>
> It may not have a TransactionId yet.
How is this a problen? If it ever gets one, it will be in the future.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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