Re: mod_dav_svn and multiple apache processes

Yes, mod_dav_svn may open and close BDB databases multiple times over the
course of a commit.

HTTP/WebDAV is a stateless protocol. "Stateless" means (in this case) that
a commit -- which consists of many client->server requests (OPTIONS,
MKACTIVITY, PROPPATCH, CHECKOUT, PUT, COPY, MERGE, ...) and their responses
-- happens in phases, each phase carrying enough information to remind the
server of what the previous phases accomplished (and/or how to figure that
out for itself). Because of this, you could theoretically shutdown and
restart your Apache server between each and every request of a single
Subversion commit operation, and things would work just fine.

I think you are confusing a number of concepts: the HIGH-LEVEL SVN COMMIT
OPERATION, which happens using one or more CONNECTIONS to the Apache server,
through each of which one or more REQUESTS is sent and responses received,
all of which work to make piecemeal modifications to a single SUBVERSION
REPOSITORY COMMIT TRANSACTION. Until to understand those elements, not much
more of what I say is going to make very much sense.

Viacheslav Zholudev wrote:
> Hi Michael,
>
> I had a closer look and I figured out the following. SVN may open and
> close BDB databases MORE than once during ONE svn commit (i.e. during 1
> svn transaction), and create svn_fs_t objects multiple times. Is it
> normal behavior? Could it be because Apache decides to clean caches, and
> then recreates an svn_fs_t object since the previous one was cleaned up
> and closed? As far as understood from your former emails, only one cached
> svn_fs_t object should be used by mod_dav_svn PER 1 svn transaction (e.g.
> commit). But I'm seeing the opposite situation...
>
> Could you please clarify? Thanks a lot for your time.
>
> Best, Vyacheslav
>
>
> On Dec 2, 2009, at 4:01 PM, C. Michael Pilato wrote:
>
>> Viacheslav Zholudev wrote:
>>> 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?
>> Today's Subversion clients won't do that. They serialize the
>> transmission of file contents towards the server. But putting that
>> aside, the BDB code keeps one file's contents in the 'strings' table
>> separate from another's by assigning the contents to different database
>> keys. So while a single client may not write to two different files in
>> the same transaction, it's certainly the case that multiple clients
>> could be tossing file contents for multiple files into the 'strings'
>> table simultaneous. The code does the right thing though -- it's not
>> like you're going to get corruption or anything that appears like a
>> file has interleaved content from various sources.
>>
>> What's the source of your interest? Are you seeing a problem?
>>
>> -- C. Michael Pilato <cmpilato_at_collab.net> CollabNet <>
>> www.collab.net <> Distributed Development On Demand
>>
>
> Best, Vyacheslav
>
>
>

-- 
C. Michael Pilato <cmpilato_at_collab.net>
CollabNet   <>   www.collab.net   <>   Distributed Development On Demand
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