Re: RAM-only temporary tables

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: RAM-only temporary tables
Date: 2008-11-06 18:36:44
Message-ID: 4912E4DC.EE98.0025.0@wicourts.gov
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>>> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> it's difficult to tell how much
> physical I/O results from the create or unlink syscalls. It might
be
> interesting to make a test program that just creates 4000 files

We use xfs with noatime for our databases.

In a fresh subdirectory of such a mountpoint:

for ((i=0 ; i < 4000 ; ++i)) ; do touch $i ; done

causes 44,969 block writes

> and then
> removes them again, and see what sort of load you see from that.

rm *

causes 26,820 block writes

That would make the file creation and unlink just under half the load.

-Kevin

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