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Re: fsfs revprop packing in f5 Re: Does fsfs revprop packing no longer allow usage of traditional backup software?

From: Philip Martin <philip.martin_at_wandisco.com>
Date: Thu, 07 Jul 2011 14:54:10 +0100

Daniel Shahaf <danielsh_at_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.martin_at_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 :)

>> 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
'svnsync sync' would do about 2.5MB write IO per invocation just setting
r0 revprops.

-- 
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Received on 2011-07-07 15:54:47 CEST

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