| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Re: [COMMITTERS] pgsql: Tune GetSnapshotData() during Hot Standby by avoiding loop |
| Date: | 2010-04-19 14:47:25 |
| Message-ID: | 1271688445.8305.18966.camel@ebony |
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| Lists: | pgsql-committers pgsql-hackers |
On Mon, 2010-04-19 at 17:44 +0300, Heikki Linnakangas wrote:
> > Choices are
> >
> > 1. Check RecoveryInProgress() once outside of lock, plus wild rumour of
> > Murphy
> >
> > 2. Check RecoveryInProgress() before and after holding lock
> >
> > 3. Check RecoveryInProgress() while holding lock
>
> 4. Check RecoveryInProgress() once outside of lock, and scan the
> ProcArray anyway, just in case. That's what we did before this patch.
> Document that takenDuringRecovery == true means that the snapshot was
> most likely taken during recovery, but there is some race conditions
> where takenDuringRecovery is true even though the snapshot was taken
> just after recovery finished. AFAICS all of the other current uses of
> takenDuringRecovery work fine with that.
Checking RecoveryInProgress() is much cheaper than scanning the whole
ProcArray, so (4) is definitely worse than 1-3.
--
Simon Riggs www.2ndQuadrant.com
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