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Re: Buffer access rules, and a probable bug

From: ncm(at)zembu(dot)com (Nathan Myers)
To: pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Buffer access rules, and a probable bug
Date: 2001-07-03 19:36:19
Message-ID: 20010703123619.H1466@store.zembu.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Jul 02, 2001 at 09:40:25PM -0400, Tom Lane wrote:
> 
> 4. It is considered OK to update tuple commit status bits (ie, OR the
> values HEAP_XMIN_COMMITTED, HEAP_XMIN_INVALID, HEAP_XMAX_COMMITTED, or
> HEAP_XMAX_INVALID into t_infomask) while holding only a shared lock and
> pin on a buffer.  This is OK because another backend looking at the tuple
> at about the same time would OR the same bits into the field, so there
> is little or no risk of conflicting update; what's more, if there did
> manage to be a conflict it would merely mean that one bit-update would
> be lost and need to be done again later.

Without looking at the code, this seems mad.  Are you sure?

Nathan Myers
ncm(at)zembu(dot)com

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