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: 2010-12-14T22:14:28Z
Lists: pgsql-hackers

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

On Tue, Dec 14, 2010 at 4:55 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 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.

Good point.

-- 
Robert Haas
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