Re: Do we need so many hint bits?

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org, Merlin Moncure <mmoncure(at)gmail(dot)com>
Subject: Re: Do we need so many hint bits?
Date: 2012-11-18 14:19:31
Message-ID: 201211181519.33154.andres@2ndquadrant.com
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On Sunday, November 18, 2012 03:07:01 AM Jeff Davis wrote:
> Process A (process that clears a VM bit for a data page):
> 1. Acquires exclusive lock on data buffer
> 2. Acquires exclusive lock on VM buffer
> 3. clears VM bit
> 4. Releases VM buffer lock
> 5. Releases data buffer lock

Well, but right this is a rather big difference. If vm pages get
unconditionally locked all the time we will have a huge source of new
contention as they are shared between so many heap pages.

Andres
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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