| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Noah Misch <noah(at)leadboat(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe |
| Date: | 2011-12-20 16:34:58 |
| Message-ID: | 20007.1324398898@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Noah Misch <noah(at)leadboat(dot)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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