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Re: Page Checksums + Double Writes

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, 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
Subject: Re: Page Checksums + Double Writes
Date: 2011-12-23 20:25:57
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
> 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?

Hmm ... once they've been written out from the SLRU arena, yes.  In fact
you don't need to go back as far as global xmin --- *any* valid xmin is
a sufficient boundary point.  The only real problem is to know whether
the data's been written out from the shared area yet.

This idea has potential.  I like it better than Robert's, mainly because
I do not want to see us put something in place that would lead people to
try to avoid rollbacks.

			regards, tom lane

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