Hi Michael,
thanks for the answer. It sufficiently clarifies things for me. However, I have one more question:
Let's assume that SVN client commits two big files in the same SVN transaction. Could it happen that mod_dav_svn writes pieces of those two big files to the "strings" simultaneously? I.e. part1_file1, part1_file2, part2_file1, part2_file2 or in some other mixed order?
Thanks,
Vyacheslav
On Dec 2, 2009, at 3:29 PM, C. Michael Pilato wrote:
> Viacheslav Zholudev wrote:
>> Hi,
>>
>> Please help me out in understanding internals of BDB-based subversion.
>>
>> When committing files to my repository over HTTP, I noticed that Apache uses multiple processes to serve my commit. Here I've got a couple of questions:
>> 1) Shouldn't Apache use only one process per SVN transaction? I thought it was the case.
>
> Not necessarily. Subversion was designed to allow for piecemeal transaction
> build-up and commit. Apache was designed to give its admins the ability to
> limit the number of requests and such that any given child process handles.
>
>> 2) How does mod_dav_svn distribute commit work among processes?
>
> You give mod_dav_svn more credit than it deserves. Subversion clients don't
> realize that they are talking to more than one Apache process, and generally
> *aren't* talking to more than one Apache process at any given time. All the
> client knows is "I'm talking to the server". All that mod_dav_svn knows is
> "Apache has asked me to handle this request". It's Apache itself that
> decides which child process to hand the request off to, and it does so
> without any particularly interesting heuristics. There's nothing like a
> load balancer or anything of that sort at work here.
>
>> 3) May mod_dav_svn uses different svn_fs_t objects for writing the same file to the SVN's backend?
>> 4) How mod_dav_svn decides when to open and close svn_fs_t* object
>
> A given mod_dav_svn process should only use one svn_fs_t per request,
> because if I'm not mistaken, mod_dav_svn caches the svn_repos_t and svn_fs_t
> objects that it opens in Apache's connection pool (a block of memory whose
> lifetime matches an Apache connection). Those objects are closed when the
> connection pool is destroyed (that is, when Apache closes the connection).
>
>> 5) Where I can read more about mod_dav_svn (except the code)
>
> Heh. Um ... Er ... what documentation?
>
> --
> C. Michael Pilato <cmpilato_at_collab.net>
> CollabNet <> www.collab.net <> Distributed Development On Demand
Best,
Vyacheslav
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Received on 2009-12-02 15:52:29 CET