[MERGE] BEncode Revision Serializer

[John Arbash Meinel]

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...

> Anyway, I would like to postpone landing this until I've gotten some
> numbers for comparing it to the RIO based serializer, and our existing
> XML based one. (Size/speed/etc).
> 
> I'll try to get that done today.
> 
>   BB:comment
> 
> (I'm not really sure that we have a BB:wait until I give a full review :)
> 
> John
> =:->

So here are the start of some numbers. This is the size of just the
'revisions' portion after compression.

                      Raw    %    Compressed    %  Objects
dev6             3990 KiB   0%       632 KiB   6%     1043
dev7-bencode     3851 KiB   0%       647 KiB   6%     1043
dev6-rio         3840 KiB   0%       632 KiB   6%     1043

Notice that dev7-bencode is the largest of the group and dev6/dev6-rio
are about the same size.

I'm 75% sure that this is because we don't control the ordering of the
data in the bencode form.

Time to extract all 1000 Revisions:
$ TIMEIT -s "b = Branch.open('dev7-rio/m'); b.lock_read(); \
  revs = b.repository.get_ancestry(b.last_revision()); revs.pop(0); \
  b.repository.get_revisions(revs)" \ # Seed the request to avoid index
  "b.repository.get_revisions(revs)"

dev6		157 msec per loop
dev7-bencode	158 msec per loop
dev7-rio	106 msec per loop

Now, mysql revs are a bit a-typical because they have large revision
properties, with bencoded per-file messages.

Given that bencode is both larger and slower, though....

Now, I realize that 'slower' seems to contradict what Jelmer saw when
benchmarking a single revision deserialized lots of times.

Given the above, though, it would seem prudent to benchmark both the RIO
serializer and the BEncode serializer using UserTest and a bigger
dataset (like all of bzr.dev as a baseline, but MySQL would be nice...)

John
=:->

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