Re: ALTER TABLE lock strength reduction patch is unsafe - Mailing list pgsql-hackers

From Tom Lane
Subject Re: ALTER TABLE lock strength reduction patch is unsafe
Date
Msg-id 20007.1324398898@sss.pgh.pa.us
Whole thread Raw
In response to Re: ALTER TABLE lock strength reduction patch is unsafe  (Noah Misch <noah@leadboat.com>)
Responses Re: ALTER TABLE lock strength reduction patch is unsafe  (Simon Riggs <simon@2ndQuadrant.com>)
List pgsql-hackers
Noah Misch <noah@leadboat.com> writes:
> On Mon, Dec 19, 2011 at 11:13:57PM -0500, Tom Lane wrote:
>> ... but this performance test seems to me to be entirely misguided,
>> because it's testing a situation that isn't going to occur much in the
>> field, precisely because the syscache should prevent constant reloads of
>> the same syscache entry.

>> [ideas for more-realistic tests]

> Granted, but I don't hope to reliably measure a change in a macro-benchmark
> after seeing a rickety 2% change in a micro-benchmark.

No, I'm not sure about that at all.  In particular I think that
CatalogCacheFlushCatalog is pretty expensive and so the snapshot costs
could be a larger part of a more-realistic test.
        regards, tom lane


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