| From: | Hannu Krosing <hannu(at)krosing(dot)net> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Peter Eisentraut <peter_e(at)gmx(dot)net>, Thomas Lockhart <lockhart(at)fourpalms(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Syscaches should store negative entries, too |
| Date: | 2002-01-30 04:19:45 |
| Message-ID: | 1012364385.2055.0.camel@rh72.home.ee |
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| Thread: | |
| Lists: | pgsql-hackers |
On Wed, 2002-01-30 at 10:56, Tom Lane wrote:
>
> FWIW, I believe that in typical scenarios there *is* no competition as
> the syscache never gets full enough to have anything age out. In the
> regression tests my little stats addition shows no run with more than
> 266 cache entries accumulated; the average end-of-run cache population
> is 75 entries. Syscache is currently configured to allow 5000 entries
> before it starts to drop stuff.
Are there _any_ tests where it does start to drop stuff ?
In other words - is the stuff-dropping part tested reasonably recently
(or at all) ?
> The regression tests are probably not representative, but if anything
> I'd expect them to hit a wider variety of tables on an average run than
> typical applications do.
>
> Bottom line: it's not apparent to me why the cache policy should be
> anything but straight LRU across both positive and negative entries.
In other words we should cache Frequently Asked Questions and not
Frequently Found Answers ;)
-------------
Hannu
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