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Re: More FOR UPDATE/FOR SHARE problems

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Greg Stark <greg(dot)stark(at)enterprisedb(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, "npboley(at)gmail(dot)com" <npboley(at)gmail(dot)com>
Subject: Re: More FOR UPDATE/FOR SHARE problems
Date: 2009-01-24 23:47:51
Message-ID: 1232840871.6610.40.camel@jdavis (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Sat, 2009-01-24 at 19:45 +0000, Greg Stark wrote:
> There already is quite an extensive discussion of how FOR UPDATE  
> behaves including these kinds of violations.

Not in the documentation, that I can see. And I think it's important
that it be there for the reasons I mentioned.

Can you refer me to the dicussion that you're talking about? I don't
remember any discussion that points out that FOR UPDATE/FOR SHARE is
broken in the simple case of a simple WHERE clause.

> What you propose is interesting though. It would have been impossible  
> before subtransactions but it's doable now. Still the performance  
> might be unusable for complex queries. It's basically generalizing the  
> logic a serializable transaction would take to a read committed command.

It might be effective for queries that are highly selective on large
tables. Still has strange deadlock possibilities, but I think that's the
case already.

	Jeff Davis

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