BDB vs FSFS - OMG!

Hey there,

So, I did some measurement based with a mirror of the boost repository.
That is a 82,362 revs, 971,599 changes repository mainly containing
source code. It is surprising how much BDB has fallen behind.

Tests were run on 64 bit Ubuntu 12.10 with BDB 5.1. Repository configs,
created with latest /trunk:

(1): --fs-type bdb --bdb-txn-nosync; auto log removal implied
(2): --fs-type fsfs
(3): --fs-type fsfs + directory deltification + compressed revprops

Repository sizes (BDB is ~4GB) don't look too bad but FSFS is still
a clear winner:

(1) : (2) : (3)
3.1 : 1.8 : 1 disk usage

Now some runtime numbers. svnadmin tests were run with '-M 4000' cache
size.

(1): (2) : (3) performance (inverted runtime)
 1 : 3.6 : 3.5 svnadmin load (user + sys)
 1 : 26 : 20 svnadmin verify

Client test were run with svn-bench against svnserve ('--cache-revprops yes
--cache-fulltexts yes --cache-txdeltas yes -M 4000 -c 0 --client-speed 10').
Two runs were made for each operation and svnserve was restarted after
the second run. BDB did not show an improvement in the second runs.

(1): (2) : (3) performance (inverted runtime)
 1 : 3.6 : 3.5 svn-bench null-export (1st run)
 1 : 52 : 47 (2nd run)
 1 : 21 : 18 svn-bench null-log -v (1st run)
 1 : 136 : 134 (2nd run)
 1 : 14 : 13 svn-bench null-log -v -g (1st run)
 1 : 41 : 40 (2nd run)
 1 : 6.3 : 5.7 svn-bench null-list -v -R (1st run)
 1 : 16 : 16 (2nd run)

Given these numbers, merge operations are probably also much slower with
BDB.

-- Stefan^2.

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