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Re: svn commit: r1657451 - in /subversion/branches/reuse-ra-session: ./ subversion/libsvn_client/

From: Branko Čibej <brane_at_wandisco.com>
Date: Thu, 05 Feb 2015 09:33:57 +0100

On 05.02.2015 01:59, Branko Čibej wrote:
> On 05.02.2015 01:44, brane_at_apache.org wrote:
>> Author: brane
>> Date: Thu Feb 5 00:44:57 2015
>> New Revision: 1657451
>> URL: http://svn.apache.org/r1657451
>> Log:
>> On the reuse-ra-session branch: Add explicit session reuse in libsvn_client.
> Anyone who's interested in the RA session cache, please take time to
> review this commit.
> All tests pass for me (ra_local, ra_svn and ra_dav) and I re-read the
> diffs about five times to check that sessions are being released to
> cache only when it's certain that they're valid. But I'd really like to
> have a few more pairs of eyes on this, because there's potential for
> some nasty bugs being introduced.

To get a feeling for what the RA session cache gains us, here are
summarized stats from a few test runs:

  * client-test:
    request:21 open:13 close:3 release:18 reuse:8 cleanup:0

  * merge_tests.py:
    request:4079 open:3812 close:20 release:3431 reuse:267 cleanup:62

  * externals_tests.py:
    request:1005 open:597 close:5 release:996 reuse:408 cleanup:4

To get a feeling for what this means: during the externals test run, we
got about a thousand requests to open a RA session through
libsvn_client, 40% of which were serviced by the reuse of a previously
released session. Only 9 sessions were closed due to pool clean-up, 4 of
which were owned by pools with a lifetime longer than the client
context's pool.

Our tests are not an ideal showcase for session reuse, because they run
a zillion short-lived processes; I expect something like TortoiseSVN
could benefit from the cache far more. Still, the externals-tests
results seem to show that even our command-line client can benefit from
session reuse.

See the comment in the definition of svn_client__ra_cache_t in
ra_cache.c for an explanation of the various numbers. The following
condition should always be true:

    request == close + release + cleanup.

-- Brane
Received on 2015-02-05 09:36:45 CET

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