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RE: svn commit: r1092660 - in /subversion/trunk/subversion/libsvn_wc: adm_ops.c crop.c wc_db.c wc_db.h

From: Bert Huijben <bert_at_qqmail.nl>
Date: Fri, 15 Apr 2011 21:46:27 +0200

> -----Original Message-----
> From: Greg Stein [mailto:gstein_at_gmail.com]
> Sent: vrijdag 15 april 2011 20:51
> To: dev_at_subversion.apache.org
> Subject: Re: svn commit: r1092660 - in
> /subversion/trunk/subversion/libsvn_wc: adm_ops.c crop.c wc_db.c
> wc_db.h
>
> On Fri, Apr 15, 2011 at 07:03, <rhuijben_at_apache.org> wrote:
> >...
> > Instead of installing a wq operation to remove records from the database
> > in the commit processing, just perform the operation directly.
> >
> > Working queue operations are for synchronizing the working copy with the
> > database. In this case the working copy doesn't change at all.
>
> They are also used to ensure that N separate database operations are
> all completed. You don't want the deletes to happen without the rest
> of the commit processing, too.
>
> Given that... does this change still make sense? I'm not really sure
> of the node removal within the larger context of the commit.

Yes. It removes only the shadowed operations, which is safe
 Once the commit for this node has been processed the shadowed operations
below this layer are invalid by itself, as they rely on their op_roots,
which are being removed by the processing. (And this happens in the same
transaction as the removal of that op_root). So it actually avoids db
instability.

Before this patch series we did:
Queue one operation
Queue one operation
Run operations
(db is in an unstable situation here)
Queue one operation
Run one operation,
(etc)

(and some of these operations were not restartable yet)

But why queue db-only changes when we can just perform them directly with
the same atomic guarantees?
(The SQLite transaction guarantees that the db_op_commit_node is completely
evaluated or not at all; same guarantee as queuing a single wq operation to
perform that operation)

The code shifting now even allows moving all the processing (and the queuing
of the wq operations) in a single sqlite transaction which would improve
stability and performance even further.

        Bert

>
> Cheers,
> -g
Received on 2011-04-15 21:47:04 CEST

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