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Re: Page Checksums + Double Writes

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Simon Riggs <simon(at)2ndquadrant(dot)com>, alvherre(at)commandprompt(dot)com, david(at)fetter(dot)org, pgsql-hackers(at)postgresql(dot)org, tgl(at)sss(dot)pgh(dot)pa(dot)us
Subject: Re: Page Checksums + Double Writes
Date: 2011-12-23 19:57:42
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On 12/23/11, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Dec 23, 2011 at 11:14 AM, Kevin Grittner
> <Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
>> Thoughts?
> Those are good thoughts.
> Here's another random idea, which might be completely nuts.  Maybe we
> could consider some kind of summarization of CLOG data, based on the
> idea that most transactions commit.

I had a perhaps crazier idea. Aren't CLOG pages older than global xmin
effectively read only?  Could backends that need these bypass locking
and shared memory altogether?

> An obvious problem is that, if the abort rate is significantly
> different from zero, and especially if the aborts are randomly mixed
> in with commits rather than clustered together in small portions of
> the XID space, the CLOG rollup data would become useless.  On the
> other hand, if you're doing 10k tps, you only need to have a window of
> a tenth of a second or so where everything commits in order to start
> getting some benefit, which doesn't seem like a stretch.

Could we get some major OLTP users to post their CLOG for analysis?  I
wouldn't think there would be much security/propietary issues with
CLOG data.



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