From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Fabrízio de Royes Mello <fabriziomello(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Doubt about AccessExclusiveLock in ALTER TABLE .. SET ( .. ); |
Date: | 2015-08-04 08:55:03 |
Message-ID: | 20150804085503.GA19705@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2015-08-03 14:15:27 +0900, Michael Paquier wrote:
> On Sat, Aug 1, 2015 at 9:20 PM, Andres Freund wrote:
> > On August 1, 2015 2:17:24 PM GMT+02:00, Michael Paquier wrote:
> >>> For instance, if you told me to choose between ShareLock and
> >>> ShareUpdateExclusiveLock I wouldn't know which one is strongest. I
> >>> don't it's sensible to have the "lock mode compare" primitive
> >>honestly.
> >>> I don't have any great ideas to offer ATM sadly.
> >>
> >>Yes, the thing is that lowering the lock levels is good for
> >>concurrency, but the non-monotony of the lock levels makes it
> >>impossible to choose an intermediate state correctly.
> >
> > How about simply acquiring all the locks individually of they're different types? These few acquisitions won't matter.
>
> As long as this only applies on master, this may be fine... We could
> basically pass a LOCKMASK to the multiple layers of tablecmds.c
> instead of LOCKMODE to track all the locks that need to be taken, and
> all the relations open during operations.
This sounds far too complicated to me. Just LockRelationOid() the
relation with the appropriate level everytime you pass through the
function?
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