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Re: SSI patch version 14

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: SSI patch version 14
Date: 2011-01-31 20:15:42
Message-ID: 1296504942.7673.13.camel@jdavis-ux.asterdata.local (view raw, whole thread or download thread mbox)
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On Mon, 2011-01-31 at 13:55 -0600, Kevin Grittner wrote:
> Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>  
> > I don't think this function really cares about the visibility with
> > respect to the current snapshot, right?
>  
> What it cares about is whether some other particular top level
> transaction wrote a tuple which we *would* read except that it is
> not visible to us because that other top level transaction is
> concurrent with ours.

Or a tuple that you *are* reading, but is being deleted concurrently,
right? Or has been deleted by an overlapping transaction?

> If so, we want to flag a read-write conflict
> out from our transaction and in to that other transaction.

It still seems like HTSV would suffice, unless I'm missing something.

I think "visible" is still needed though: it matters in the cases
HEAPTUPLE_RECENTLY_DEAD and HEAPTUPLE_LIVE. For the former, it only
allows an early exit (if !visible); but for the latter, I think it's
required.

Regards,
	Jeff Davis


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