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From Daniel Shahaf <danie...@elego.de>
Subject Re: svn commit: r1296604 - in /subversion/trunk/subversion/libsvn_fs_fs: caching.c fs.h fs_fs.c
Date Sun, 04 Mar 2012 10:06:34 GMT
Hyrum K Wright wrote on Sat, Mar 03, 2012 at 09:51:07 -0600:
> On Sat, Mar 3, 2012 at 5:31 AM,  <stefan2@apache.org> wrote:
> > Author: stefan2
> > Date: Sat Mar  3 11:31:17 2012
> > New Revision: 1296604
> >
> > URL: http://svn.apache.org/viewvc?rev=1296604&view=rev
> > Log:
> > Certain operations, e.g. svn ls, will contain timestamp and author
> > information from many different revisions.  A list of all projects
> > in the root of the wordpress repository will open, read and close
> >>75.000 revision property files (3 reads for each list entry)
> >
> > This commit implements revprop caching.  It will be activated as
> > part of the full-text caching option.
> >
> > Since revprops may be written by other threads or processes, we
> > need to track the revprop changes.  A new special file contains a
> > counter that will be increased each time revision properties get
> > rewritten.
> >
> > This counter is internally called "revprop generation" and will be
> > read upon the first revprop access for given fs_t.  Later changes
> > may remain invisible for that fs_t.  This behavior is in line with
> > our revprop handling in other parts of FS_FS.  If a revprop gets
> > rewritten, the fs_t doing the write will use the new generation
> > from that point on and will thus see all caches up to and including
> > its own.
> >
> > Since the revprop generation becomes part of the cache key, each
> > fs_t will only see revprops from its generation.  It may also
> > create new cache entries tagged with that generation, i.e. those
> > would appear to be outdated for newer fs_t.  But that will simply
> > cause a benign false negative upon lookup.  No fs_t will see
> > data that got replaced before that fs_t was created.
> 
> How does this potentially interact with revprop packing?
> 

I believe the two features are orthogonal.

> -Hyrum
> 
> -- 
> 
> uberSVN: Apache Subversion Made Easy
> http://www.uberSVN.com/

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