Re: per table random-page-cost?

From: Stefan Moeding <pgsql(at)moeding(dot)net>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: per table random-page-cost?
Date: 2009-10-24 06:00:54
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Josh Berkus writes:

> Now, if we had an OS which could be convinced to handle caching
> differently for different physical devices, then I could see wanting
> this setting to be per-tablespace. For example, it would make a lot of
> sense not to FS-cache any data which is on a ramdisk or superfast SSD
> array. The same with archive data which you expected to be slow and
> infrequently accessed on a NAS device. If your OS can do that, while
> caching data from other sources, then it would make sense.
> However, I don't know any current OS which allows for this. Does anyone
> else?

Isn't bypassing the buffer cache exactly what direct I/O is about?
Solaris UFS has a "forcedirectio" mount option, AIX JFS2 calls it "dio"
and Veritas VxFS uses the "convosync=direct" option to disable caching
the content of the filesystem.


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