Stefan Fuhrmann wrote on Wed, Aug 27, 2014 at 14:49:23 +0200:
> On Wed, Aug 27, 2014 at 2:30 PM, Daniel Shahaf <d.s_at_daniel.shahaf.name>
> wrote:
>
> > Stefan Fuhrmann wrote on Tue, Aug 26, 2014 at 17:04:27 +0200:
> > > Here the guarantees and limitations of the new implementation:
> > >
> >
> > I haven't had a chance to look at the code (sorry), but two quick
> > questions based on this summary:
> >
> > > * No lost updates in revprop file contents even if the
> > > SVN caches should be stale.
> > > * A connection (svn_fs_t) will always see at least all
> > > changes up to and including its own last revprop change.
> > > * A new connection will always see all changes made
> > > up to the point the connection got created.
> > >
> > > * On Windows and Unixoids, readers will always see
> > > the latest data if they are on the same machine as the
> > > writing process.
> > > * Depending on OS read cache configuration and if the
> > > repository is shared between machines, open connections
> > > *might* no see revprop updates or might see them delayed
> > > (the open revprop generation file handle may see a stale
> > > OS file buffer).
> >
> > Is starvation possible? i.e., is it possible for the delay to be
> > indefinite (assume the reader fs_t does no write operations)? I assume
> > the delay would be finite and bounded by a constant if the shared disk's
> > local file handles have this property.?
> >
>
> This entirely depends on if and when your cluster file system
> configuration makes remote changes visible to already open
> file handles. Worst case: an existing open connection never
> sees the revprop generation bump and will read new data only
> if there is no (old) data in cache for the respective revision.
>
>
> > Is linearizability guaranteed? i.e., if the repository is load-balanced
> > across four servers, and I do 'svn ps alpha 1; svn ps beta 2; svn ps
> > gamma 3; svn pl', is it possible for the last process to see beta
> > without seeing alpha? (e.g., if each svn process gets load balanced to
> > a different server.)
> >
>
> Writes are handled as they are today, i.e. the cache get bypassed
> even for the read step (get all revprops) in a ps operation.
> Because the last command, svn pl, opens a new connection,
> it will see up-to-date data.
Thanks for the clarifications :)
Received on 2014-08-27 14:53:24 CEST