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Re: Logical to physical page mapping

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Jan Wieck <JanWieck(at)yahoo(dot)com>,PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Logical to physical page mapping
Date: 2012-11-06 03:11:56
Message-ID: 20121106031156.GL19099@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Oct 29, 2012 at 07:05:39AM -0400, Robert Haas wrote:
> Yet another idea we've tossed around is to make only vacuum records
> include FPWs, and have the more common heap insert/update/delete
> operations include enough information that they can still be applied
> correctly even if the page has been "torn" by the previous replay of
> such a record.  This would involve modifying the recovery algorithm so
> that, until consistency is reached, we replay all records, regardless
> of LSN, which would cost some extra I/O, but maybe not too much to
> live with?  It would also require that, for example, a heap-insert
> record mention the line pointer index used for the insertion;
> currently, we count on the previous state of the page to tell us that.
>  For checkpoint cycles of reasonable length, the cost of storing the
> line pointer in every WAL record seems like it'll be less than the
> cost needing to write an FPI for the page once per checkpoint cycle,
> but this isn't certain to be the case for all workloads.

This last idea has the most promise for me.  Vacuum is far less common
than row modification writes.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +


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