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RE: svn commit: r1716575 - in /subversion/trunk/subversion/libsvn_ra_serf: commit.c ra_serf.h util.c

From: Bert Huijben <bert_at_qqmail.nl>
Date: Thu, 26 Nov 2015 10:03:44 +0100

> -----Original Message-----
> From: Ivan Zhakov [mailto:ivan_at_visualsvn.com]
> Sent: donderdag 26 november 2015 09:54
> To: Bert Huijben <bert_at_qqmail.nl>
> Cc: dev_at_subversion.apache.org
> Subject: Re: svn commit: r1716575 - in
> /subversion/trunk/subversion/libsvn_ra_serf: commit.c ra_serf.h util.c
>
> On 26 November 2015 at 11:41, Bert Huijben <bert_at_qqmail.nl> wrote:
> >> -----Original Message-----
> >> From: Ivan Zhakov [mailto:ivan_at_visualsvn.com]
> >> Sent: donderdag 26 november 2015 09:19
> >> To: dev_at_subversion.apache.org; Bert Huijben <bert_at_qqmail.nl>
> >> Subject: Re: svn commit: r1716575 - in
> >> /subversion/trunk/subversion/libsvn_ra_serf: commit.c ra_serf.h util.c
> >>
> >> On 26 November 2015 at 11:05, <rhuijben_at_apache.org> wrote:
> >> >
> >> > Author: rhuijben
> >> > Date: Thu Nov 26 08:05:36 2015
> >> > New Revision: 1716575
> >> >
> >> > URL: http://svn.apache.org/viewvc?rev=1716575&view=rev
> >> > Log:
> >> > In ra_serf: when a to-be committed file has text and property changes
> to
> >> be
> >> > applied, pipeline both requests.
> >> >
> >> This could fail over HTTP/2 if both pipelined requests will be handled
> >> by different worker threads: FSFS doesn't allow concurrent access to
> >> transactions.
> >
> > I'm surprised to learn that. I would have guessed concurrent access was
> > always part of the design of the fs layer, by the way we use it in mod_dav.
> >
> > I hope we can somehow lift that restriction, as improving commit
> performance
> > over mod_dav is high on a few wish lists.
> >
> First of all I'm not sure that concurrent *writing* could speed up
> commit: there is no fsync() calls when working with transactions. As
> far I remember svn:// also waits for every TXN operation to complete
> before sending next one, so svn:// and http:// performance should be
> the same when working over high-latency network.
>
> Another problem could be than TXN operations are have dependencies on
> each other and order is very important.

That assumes that the limit is on the server side.

I usually commit halfway over the earth... my limits are 100% in the pipeline and mostly in the latency between client and server. (100Mbit+ connections on both sides). Sending concurrent requests would be a huge performance boost.

But if we require everything in a strict order we should just immediately stop using multiple requests. If serialized access is the only thing our backends support we should just send one huge commit request. That saves a huge number of synchronize events between client and server.

Currently we send a request... wait for the result... (server waiting for us) send a request... wait for the result.

And more of that...

Removing a tempfile here or there isn't going to help if we can't remove the waiting. We can't change the wire (or light) speed between client and server.

We could design the request to return the same intermediate results in the request body as we do now, with only a fraction of the synchronization points.

But this is the other way around as the intensions we had with HTTPv2 around 1.7. There we tried to do things the HTTP way by optimal pipelining.

        Bert
Received on 2015-11-26 10:04:12 CET

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