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Re: [PATCH] Move .svn/lock files into the sdb

From: Hyrum K. Wright <hyrum_at_hyrumwright.org>
Date: Thu, 1 Oct 2009 08:46:17 -0400

On Oct 1, 2009, at 5:50 AM, Bert Huijben wrote:

>> -----Original Message-----
>> From: Hyrum K. Wright [mailto:hyrum_at_hyrumwright.org]
>> Sent: woensdag 30 september 2009 23:09
>> To: Greg Stein
>> Cc: dev_at_subversion.tigris.org
>> Subject: [PATCH] Move .svn/lock files into the sdb
>>
>> Greg, et. al.,
>> The attached patch is an attempt to move the .svn/lock files into a
>> separate table in .svn/wc.db. The reason to do this is so that we
>> can
>> use the sdb to manage the locked status of a directory, particularly
>> as we start using svn_wc__entry_modify2(), which currently does *not*
>> do a write check on the access baton. Eventually, I plan to add a
>> member to pdh->wcroot which moves the in-memory state from the access
>> baton to wc_db.
>
> This patch doesn't solve the issues with svn_wc__entry_modify2().

Correct. This is planned for a followup patch which will add a LOCKED
member to the wcroot. This member will convey similar information as
svn_wc_adm_access_t.type, and help answer the question "do I own the
lock?" By putting this in a wc_db struct, we won't have a resurrect
or create access batons to answer this question.

The patch to move the lock "files" into the sdb is seen as a precursor
to the above, since it means that we can then answer the question
"does a lock exist on this path?" without having to go back into lock.c.

I (believe I) understand the corruption issues you describe below, and
that the above plan solves them. Are there any concerns about the
implementation of this patch? (I've since updated it to include the
additional columns for format 14 added in r39725.)

-Hyrum

> This patch answers the question: "Is there a lock on X?" while we
> have to
> check "Am I the owner of an existing lock on X?" or simpler "Do I
> own a lock
> that allows me to update X?"
>
> This ownership question is the only important bit when updating a
> working
> copy.
>
>
> We are not interested in whether another client has it locked in
> this case..
> We simply can't do an exclusive update without being the lock owner.
>
>
> If an exclusive update in Process 1 does a recursive switch on the
> entire
> working copy from one branch to another, you don't want another svn
> (Process
> 2) performing a move of a file below that same root at the same time..
>
> The "Is there a lock?" will just return TRUE... so the revert might be
> perfectly valid after this patch, but it could very well corrupt your
> working copy.
>
>
> A "Am I the lock owner?" check will return FALSE, so the revert will
> not
> happen.
>
>
>
> Your recent changes replaced a few of the "Am I the lock owner?"
> questions
> with "Is there a lock?" and this new api makes it easier to do the
> WRONG
> THING.
>
>
> Moving the lock files in the DB is a completely different thing,
> that is
> unrelated to this question, and something that should+could happen
> independently
>
>
>
> If we want multiple locks on a working copy later we could just
> write the
> locked roots in a db table and keep a record on the locks we own.
> Every path
> below a locked path is locked by the wc_db. (Very cheap to check as we
> usually just lock one path.. so one dirent_is_ancestor() check is
> enough).
>
> (A proper transaction around inserting the lock can handle parent
> and child
> locks without the extreme penalty we have in WC-1.0)
>
>
> We could write a process identifier + workstation name or something
> with the
> lock in the db to specify who owns it for better error messages, but
> the
> real knowledge is in owning the lock itself... which is currently only
> handled via the flag in the access batons. And you can't just put
> that
> knowledge in the database and think you're done with that.
>
>
> Bert
>

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Received on 2009-10-01 14:46:31 CEST

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