| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Florian Pflug <fgp(at)phlo(dot)org> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org, Bruce Momjian <bruce(at)momjian(dot)us>, Greg Smith <greg(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Subject: | Re: max_standby_delay considered harmful |
| Date: | 2010-05-10 11:57:23 |
| Message-ID: | AANLkTikEFWm3YgU0PXjwuAP8opIBEjIe2X6iMKPRW8DE@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, May 10, 2010 at 6:13 AM, Florian Pflug <fgp(at)phlo(dot)org> wrote:
> On May 10, 2010, at 11:43 , Heikki Linnakangas wrote:
>> If you're not going to apply any more WAL records before shutdown, you
>> could also just release all the AccessExclusiveLocks held by the startup
>> process. Whatever the transaction was doing with the locked relation, if
>> we're not going to replay any more WAL records before shutdown, we will
>> not see the transaction committing or doing anything else with the
>> relation, so we should be safe. Whatever state the data on disk is in,
>> it must be valid, or we would have a problem with crash recovery
>> recovering up to this WAL record and then starting up too.
>
> Sounds plausible. But wouldn't this imply that HS could *always* postpone the acquisition of an AccessExclusiveLocks until right before the corresponding commit record is replayed? If fail to see a case where this would fail, yet recovery in case of an intermediate crash would be correct.
Yeah, I'd like to understand this, too. I don't have a clear
understanding of when HS needs to take locks here in the first place.
[removing Josh Berkus's persistently bouncing email from the CC line]
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company
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