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Re: Performance degeneration issues

To: Linux XFS <xfs@xxxxxxxxxxx>
Subject: Re: Performance degeneration issues
From: pg@xxxxxxxxxxxxxxxxxx (Peter Grandi)
Date: Tue, 19 Oct 2010 17:43:48 +0100
In-reply-to: <2a05-4cbc6280-f8f-3364a400@207442557>
References: <2a05-4cbc6280-f8f-3364a400@207442557>
Resent-date: Tue, 19 Oct 2010 17:43:53 +0100
Resent-from: pg_mh@xxxxxxxxxx
Resent-message-id: <19645.51913.855447.116358@xxxxxxxxxxxxxxxxxx>
Resent-to: xfs@xxxxxxxxxxx
> Hello, I'm running a Centos 5.4 x64 Server with Raid0 HDDs and
> XFS.

> Extracting a tar archive with 6.1 million files (avg. Size
> just below 2KiB)

Ah, one of the "the file system is an optimal small record DBMS"
sort of delusions.

> is blazingly fast after the fs has been generated. But after
> some time while doing deletes/moves (need to sort those files
> by their contents) the fs performance degenerates quite badly

Very funny. "the file system is an optimal small record DBMS"
sort of delusion, only squared/cubed.

It may be amusing to hear some explanation of what "sort those
files by their contents" actually is thought to mean here, as I
have the peculiar feeling that "sort" here actually means "sort
the directory entries" (as in "deletes/moves") instead of the
inodes or the file data, as if they were the same thing.

> 8k file writes/sec to about 200).

Why is this surprising?

> Is there any way I can find out what the issue is and how I
> can help it?

Some entry level tutorial on storage systems? Some introductory
book on DBMSes?

What most amuses or depresses me is that this question or a very
similar variants gets asked quite regularly in this (and other
filesystems oriented) mailing list.

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