Horton

Re: unlogged tables vs. GIST

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, pgsql-hackers@postgresql.org
Date: 2010-12-14T21:55:05Z
Lists: pgsql-hackers

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

Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Dec 14, 2010 at 4:24 PM, Heikki Linnakangas
> <heikki.linnakangas@enterprisedb.com> wrote:
>> Hmm, the first idea that comes to mind is to use a counter like the
>> GetXLogRecPtrForTemp() counter I used for temp tables, but global, in shared
>> memory. However, that's a bit problematic because if we store a value from
>> that counter to LSN, it's possible that the counter overtakes the XLOG
>> insert location, and you start to get xlog flush errors. We could avoid that
>> if we added a new field to the GiST page header, and used that to store the
>> value in the parent page instead of the LSN.

> That doesn't seem ideal, either, because now you're eating up some
> number of bytes per page in every GIST index just on the off chance
> that one of them is unlogged.

On-disk compatibility seems problematic here as well.

			regards, tom lane