Horton

Re: unlogged tables vs. GIST

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Jeevan Chalke <jeevan.chalke@enterprisedb.com>, pgsql-hackers@postgresql.org
Date: 2013-01-15T20:56:04Z
Lists: pgsql-hackers

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

On Tue, Jan 15, 2013 at 1:58 PM, Heikki Linnakangas
<hlinnakangas@vmware.com> wrote:
>> I think what Heikki had in mind was that the copy in the index would be
>> the authoritative one, not some image in shared memory.  This'd imply
>> dirtying the root page on every insert, as well as increased contention
>> for the root page, so it might have performance problems.
>
> Not every insert, just every split. Which might still be a performance
> problem, but an order of magnitude smaller.

I think that might be acceptable from a performance point of view -
after all, if the index is unlogged, you're saving the cost of WAL -
but I guess I still prefer a generic solution to this problem (a
generalization of GetXLogRecPtrForTemp) rather than a special-purpose
solution based on the nitty-gritty of how GiST uses these values.
What's the difference between storing this value in pg_control and,
say, the OID counter?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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