[ZODB-Dev] Re: ZODB Benchmarks

[Roché Compaan]

On Wed, 2007-10-31 at 10:47 -0400, David Binger wrote:
> On Oct 31, 2007, at 7:35 AM, Roché Compaan wrote:
> 
> > Thanks for the explanation.
> 
> The actual insertion is very fast.  Your benchmark is dominated by
> the time to serialize the changes due to an insertion.
> 
> You should usually have just 2 instances to serialize per insertion of
> a new instance:  the instance itself and the b-node that points to the
> instance.  An insertion may also cause changes in 2 or several b-nodes,
> but those cases are less likely.
> 
> Serializing your simple instances is probably fast, but serializing
> the b-nodes appears to be taking much more time, and probably accounts
> for the large number of calls to persistent_id.  B-Nodes with higher
> branching factors will have more parts to serialize and they will be
> slower.  If you can cut the b-node branching factor in half, I bet your
> benchmark will run almost twice as fast.

I increased the 'DEFAULT_MAX_BUCKET_SIZE' from 30 to 30000 and
DEFAULT_MAX_BTREE_SIZE from 250 to 2500 and it didn't make any
noticeable difference. Despite this change there are still a huge amount
of unexplained calls to the 'persistent_id' method of the ObjectWriter
in serialize.py.

Running fsdump on the Data.fs confirmed that there are only 2 instances
serialized per insertion, one OOBucket and an instance of the persistent
class used for testing.

So thus far the only tweak that made a significant difference was
increasing the DB cache size from 400 to 100000. 


-- 
Roché Compaan
Upfront Systems                   http://www.upfrontsystems.co.za