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Re: testing HS/SR - 1 vs 2 performance

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Erik Rijkers <er(at)xs4all(dot)nl>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: testing HS/SR - 1 vs 2 performance
Date: 2010-04-27 18:13:33
Message-ID: 1272392013.4161.7882.camel@ebony (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Tue, 2010-04-27 at 13:52 -0400, Tom Lane wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> > v3 attached
> This patch changes KnownAssignedXidsRemove() so that failure to find
> the target XID is elog(ERROR) (ie, a PANIC, since this is in the
> startup process).  

Not in all cases. The code is correct, as far as I am aware from

> However, this comment is still there:
> 	/*
> 	 * We can fail to find an xid if the xid came from a subtransaction that
> 	 * aborts, though the xid hadn't yet been reported and no WAL records have
> 	 * been written using the subxid. In that case the abort record will
> 	 * contain that subxid and we haven't seen it before.
> 	 */
> WTF?  Either the comment is wrong or this should not be an elog
> condition.

That section of code has been rewritten many times. I think it is now
inaccurate and should be removed. I left it there because the
unfortunate history of the project has been the removal of comments and
then later rediscovery of the truth, sometimes more than once. I could
no longer reproduce that error; someone else may know differently.

 Simon Riggs 

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Subject: Re: Wierd quirk of HS/SR, probably not fixable
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