Horton

Re: unlogged tables vs. GIST

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, pgsql-hackers@postgresql.org
Date: 2010-12-17T19:33:28Z
Lists: pgsql-hackers

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  1. The GiST scan algorithm uses LSNs to detect concurrent pages splits, but

On Fri, Dec 17, 2010 at 2:31 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> Another possibly-useful thing about mandating a full page header for
>> every page is that it might give us a way of avoiding unnecessary full
>> page writes.  As I wrote previously:
>
> Could we do that via a bufmgr status bit, instead?  Heikki's idea has
> the merit that it actually reduces bufmgr's knowledge of page headers,
> rather than increasing it (since a buffer marked UNLOGGED would need
> no assumptions at all about its content).

That was my first thought, but it doesn't work.  The buffer could be
evicted from shared_buffers and read back in.  If a checkpoint
intervenes meanwhile, we're OK, but otherwise you fail to emit an
otherwise-needed FPI.

-- 
Robert Haas
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