Philip Martin wrote on Thu, Jul 07, 2011 at 14:54:10 +0100: > Daniel Shahaf <danie...@elego.de> writes: > > > Hyrum K Wright wrote on Thu, Jul 07, 2011 at 08:29:31 -0500: > >> On Thu, Jul 7, 2011 at 2:36 AM, Philip Martin > >> <philip.mar...@wandisco.com> wrote: > >> > > >> > r0 revprops are a concern, they can have different access patterns. For > >> > example a master/slave setup running svnsync once per revision (a common > >> > setup) will write the r0 pack file several times per revision. We don't > >> > want the pack file to become the dominant IO. > >> > > >> > I wonder if we could offset the shard boundaries, so that r0 is the last > >> > revision in the first shard and r1-rN is the second shard. Then r0 > >> > would be a shard on its own and the r0 pack file would be much smaller. > >> > We would have to repack the repository on upgrade but the code changes > >> > for this could be small, just +/-1 in a few places. > >> > >> Changing the offsets for all the shard boundaries is just asking for > >> trouble, as it would mean that revision shards and revprop shards > >> wouldn't match up. That seems like a pretty big "gotcha". > > I assumed we would "repack the repository on upgrade" and change the > revision shards as well. Maybe that's even worse :) >
It means that all the '% ffd->max_files_per_dir' computations need to get an off-by-one iff they are for revprops. Special-casing r0 and the first shard's manifest seems to me, too, to be preferable. > >> Instead, we could just special-case r0 revprops so that they never get > >> packed, and that the 0th shard includes r1:rN, instead of r0:rN. That > >> would only impact the 0th shard, rather than every revprop shard. > > > > +1 > > If that's easy it would be even better. > > Subversion log messages average about 400 characters, so if we take that > as standard a pack file starts at about half a MB. Something like Actually it's 499931 bytes (for the last full shard from our history). Nice estimate :-) > 'svnsync sync' would do about 2.5MB write IO per invocation just setting > r0 revprops.
