| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: I/O on select count(*) |
| Date: | 2008-05-19 15:37:58 |
| Message-ID: | 5697.1211211478@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Matthew Wakeling wrote:
>> Does it really take that long to zero out 8kB of RAM? I thought CPUs were
>> really quick at doing that!
> Yea, that was my assumption too.
You have to write the page (to be sure there is space for it on disk)
not only zero it.
This design is kind of a holdover, though, from back when we had one
ever-growing clog file. Today I'd be inclined to think about managing
it more like pg_xlog, ie, have some background process pre-create a
whole segment file at a time.
regards, tom lane
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