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Re: Opening the repository hooks environment file

From: Ben Reser <ben_at_reser.org>
Date: Tue, 2 Apr 2013 17:38:25 -0700

I've gone ahead and moved the default hooks-env to hooks-env.tmpl.
We'll still try to open the file but we won't bother to read it in or
parse a completely commented out file unless the user puts a file in
place. The .tmpl is a common pattern with hooks already so it should
add any confusion.

On Thu, Mar 28, 2013 at 2:33 PM, Bert Huijben <bert_at_qqmail.nl> wrote:
>
>
>> -----Original Message-----
>> From: Branko ─îibej [mailto:brane_at_wandisco.com]
>> Sent: donderdag 28 maart 2013 22:06
>> To: dev_at_subversion.apache.org
>> Subject: Re: Opening the repository hooks environment file
>>
>> On 28.03.2013 21:50, Bert Huijben wrote:
>> >
>> >> -----Original Message-----
>> >> From: MARTIN PHILIP [mailto:codematters_at_ntlworld.com] On Behalf Of
>> >> Philip Martin
>> >> Sent: donderdag 28 maart 2013 19:32
>> >> To: Bert Huijben
>> >> Cc: dev_at_subversion.apache.org
>> >> Subject: Opening the repository hooks environment file
>> >>
>> >> "Bert Huijben" <bert_at_qqmail.nl> writes:
>> >>
>> >>> The reading of one file for each access to the repository is a more
>> >>> than measurable slowdown when profiling operations. (Reading
>> fsfs.conf
>> >>> over and over again is one of the most expensive things apache worker
>> >>> processes do when I profiled them. I think stefan2 optimized some of
>> >>> this away)
>> >> We have already picked up one new file on every access in 1.8: the hooks
>> >> environment file. This appears to be opened and parsed for every time
>> >> mod_dav_svn opens the repository, both read and write operations.
>> >>
>> >> Perhaps we should require an explict config setting to enable the hooks
>> >> file so that we can avoid opening it when it is empty? Or perhaps we
>> >> could make the opening/parsing lazy and delay it until running a hook
>> >> thus avoiding it for read operations?
>> > Would be nice if we can read it on first use (after the hook exists check?)
>> > and then cache it.
>> >
>> > I'm not sure why this didn't turn op in the performance traces though.
>> Maybe
>> > because this file doesn't exist by default?
>>
>> Sure it does, "svnadmin create" will create a template. I think you're
>> overestimating the cost of reading such small files; it'll mostly stay
>> in RAM once it's been read, and parsing it is not all that expensive.
>
> I'm pretty sure you remember that with Subversion 1.6 running 'svn update' on ^/subversion/branches took one and a half minutes on Windows to obtain the directory locks, before it even started doing anything update related?
>
> (And this was without a virusscanner on a for that time fast desktop harddisk)
>
> Simple file operations may be cheap on one system (E.g. linux) but don't use that as a measurement for other systems. That one and a half minute operation took less than half a second on ext3/ext4.
> And this problem existed on many Subversion releases without anybody noticing... The common suggestion was "Windows is slow".
>
> Loading 'fsfs.conf' is a slow operation. Maybe because it is too big to fit in a buffer; maybe because our parsing is inefficient and even more inefficient on systems where we use "\r\n" as EOL, but it really is performance critical on Windows.
>
> I don't say that we should stop reading fsfs.conf, but why should we introduce a 'fs.conf' at the repos level for things that don't belong at that level and most likely 99% of our users will never use?
>
> fsfs contains things like sharding information which are essential for functionality. It is not a diagnostics configuration file.
>
>
>
>
> Reading a very tiny file hundreds of thousands times during a typical ra-serf test run as on our buildbot makes its impact huge. (Even when using a ramdrive). This will certainly have an impact on production Subversion servers with similar loads.
>
> But as noted earlier... our testsuite uses uncommon small files.
> But the changes applied to the files might be in the more common space.
>
>
> Bert
>
Received on 2013-04-03 02:39:00 CEST

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