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Clip Man

daniele


Daniel Einspanjer's journal

Data warehousing, ETL, BI, and general hackery


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Performance improvements at the cost of complexity
Clip Man
daniele
I discovered something that I feel is a bit of a bug in the Sun Java implementation. 

If you pass in a string to the method InetAddress.getByName(), it does a bunch of testing to see if it is a domain name or a literal IP address.
If it is an IPv4 address, it will then use String.split() to split the four parts.  String.split() uses regexes to do its work.

That means that if you are querying for hundreds or millions of addresses in a tight loop (as I've been doing), the JVM is spawning and compiling hundreds or millions of regex objects, in addition to a String array and four String objects per call.

So at first, I just worked around it by doing basic substringing instead of splitting.  That gave me about 100x performance improvement. But then I realized I was still generating four string objects for every call..

So I came up with this mapping method and it runs about 1000x faster with a near constant minimal memory footprint.

I pre-calculate a multidimensional array of shorts where each element is indexed by the literal character value - 48 of the digits making up the number 0 - 255.

With that array available, at run time, I can do a simple lookup of the short value and then do the math to get the long representation of the IP address.  I'm still generating a couple of references and a few intermediate int values, but the JIT optimizer can make quick work of that.

Linked is the test program I created to play with the different methods:  InetAddressParse test


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You're using NetBeans! How do you like it?

This was actually my first ever foray into NetBeans. I tried it out because I wanted to be able to easily run both CPU performance and Memory performance profiling. Eclipse's TPTP just wasn't cutting it either directly on my Mac or for remote profiling of my Linux server via my Mac.

Doing this testing in NetBeans was a breeze! Unfortunately, it was a big pain in the ass to try to get the actual source code project imported so I gave that up and just used NetBeans for the testing. Still using Eclipse for the actual Java project coding.

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