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Re: svn commit: r1079008 - /subversion/trunk/subversion/svnadmin/main.c

From: Philip Martin <philip.martin_at_wandisco.com>
Date: Wed, 09 Mar 2011 10:56:45 +0000

Stefan Fuhrmann <eqfox_at_web.de> writes:

> On 08.03.2011 14:46, Philip Martin wrote:
>> stefan2_at_apache.org writes:
>>
>>> Author: stefan2
>>> Date: Mon Mar 7 22:57:04 2011
>>> New Revision: 1079008
>>>
>>> URL: http://svn.apache.org/viewvc?rev=1079008&view=rev
>>> Log:
>>> Set FSFS cache default size to 16 MB. This is the same default as
>>> for everybody else, namely the server processes. Thus, it should
>>> be reasonable value on the same machines.
>> 16MB may be "reasonable" for normal usage but it still has a significant
>> effect on the testsuite. The testsuite is an unusual access pattern, it
>> runs thousands of commands on small repositories. Using a 1MB cache I
>> can run the testsuite for ra_local/FSFS in 10m15s, with 16MB cache that
>> increases to 12m30s, a 20% increase. There is a similar increase when
>> testing ra_svn/FSFS using the default Linux svnserve (a threaded
>> svnserve has a shared cache so isn't affected).
> The patch attached fixes the performance penalty
> for "make check" by disabling membuffer caches
> over ra_local by default. Since svn_ra_initialize is
> being called early in main(), the setting can later
> be overwritten by settings from e.g. a config file.
>
> Could you verify that / whether this fixes your
> performance issue?

It goes some way, but it's not as good as setting the cache size to 1MB
since it doesn't affect the svnadmin dump/load commands used by most of
the tests.

>> svnserve and svnadmin both have a -M option, was there any discussion
>> about using a single letter option for this feature?
> No.
>> This could be used
>> by the testuite to restrict the cache size, but for ra_local/FSFS
>> testing there is no way to restrict the svn client.
> As already shown in a different thread, the memory
> consumption should actually go down for any non-
> trivial repository.
>> Should we add the -M option to the svn client?
> Due to its limited applicability (FSFS via file:/// only),

There may well be large numbers of people using that for private
repositories.

As I undertand it cache initialisation includes setting the memory to
zero, and that this is partly to ensure that all the allocated memory is
really available to the process on a Linux system with overcommit
enabled. If the cache had a more lightweight initialisation then a
cache size of 16MB would probably not be a problem. Was there any
discussion about this overcommit behaviour? Linux overcommit is
configurable, why should Subversion override this? It doesn't apply to
all the other memory allocation in Subversion, so what guarantee are you
trying to provide and what are you actually providing?

-- 
Philip
Received on 2011-03-09 11:57:23 CET

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