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Re: FPI

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: FPI
Date: 2011-01-31 15:01:50
Message-ID: AANLkTin8hWGBQA5z-4wNX=-iPTYD+kduQo74YV1=q6vA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Jan 28, 2011 at 3:39 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> What happens if we (a) keep the current rule after reaching
> consistency and (b) apply any such updates *unconditionally* - that
> is, without reference to the LSN - prior to reaching consistency?
> Under that rule, if we encounter an FPI before reaching consistency,
> we're OK.  So let's suppose we don't.  No matter how many times we
> replay any initial prefix of any such updates between the redo pointer
> and the point at which we reach consistency, the state of the page
> when we finally reach consistency will be identical.  But we could get
> hosed if replay progressed *past* the minimum recovery point and then
> started over at the previous redo pointer.  If we forced an immediate
> restartpoint on reaching consistency, that seems like it might prevent
> that scenario.

Actually, I'm wrong, and this doesn't work at all.  At the time of the
crash, there could already be pages on disk with LSNs greater than the
minimum recovery point.  Duh.

It was such a good idea in my head...

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

In response to

  • Re: FPI at 2011-01-28 20:39:33 from Robert Haas

Responses

  • Re: FPI at 2011-02-01 02:28:43 from Robert Haas

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