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From: Lukas Eder <mar09086@adobe.com>
To: "oak-dev@jackrabbit.apache.org" <oak-dev@jackrabbit.apache.org>
Date: Thu, 16 May 2013 15:13:41 +0100
Subject: MongoMK Revision.toString() usage
Thread-Topic: MongoMK Revision.toString() usage
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Hello,

I've been investigating Oak performance and found a couple of cases where M=
ongoMK makes use of stringified versions of the org.apache.jackrabbit.mongo=
mk.Revision type. One example of such a problem was reported here [1].

I have a couple of things that I'd like to talk about, concerning Revision.=
toString() usage:

 1.  toString() should hardly ever be used for anything other than debuggin=
g. It is very hard to find relevant matching references of Object.toString(=
) in a Java code base. In other words, toString() is almost not "refactorab=
le". E.g. is hard to predict what side-effects a change to the toString() b=
ehaviour will have. Ideally, toString() should delegate to another method, =
such as format(), where the predicable logic is really implemented.
 2.  Revision has a much lower memory footprint than its string representat=
ion, so it is actually be better suited to be used in maps, caches, etc.
 3.  MongoMK.isCommitted() is an example that shows how revisions are unnec=
essarily transformed back and forth to strings.

In a larger profiling session, Revision.fromString() and Revision.toString(=
) accounted for a total of around 1.5% of all CPU time on my machine.
This may seem like micro-optimisation to some, but I think that we should t=
ake these things seriously, as they might add up to a significant amount of=
 CPU and memory waste, if practiced across a large code base.

Please, let me know what you think.

Cheers
Lukas

[1]: https://issues.apache.org/jira/browse/OAK-825

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