Head over to google code and grab yourself a copy.

Links:

• Hood Beta 2

It’s called “Hood” for neighbourhood and allows you to mark places or people around a place of activity of yours, called hood. it is meant to foster collaboration / tips on local places etc.

It’s Spring Web Application demonstrating some techniques of working with jcouchdb. It’s an eclipse WTP/Spring IDE project with all dependencies you need besides couchdb and tomcat or another servlet container.

Stay tuned for hood to grow into a fullblown app.

Links:

• Hood Alpha – download at code.google.com
• Hood Beta 2 – download at code.google.com

jcouch db logo

This Article is also available in Deutsch.

I’ve been frustrated with the old blog code and the old design for some time now and wanted to redo everything and already started multiple attempts in various technological reincarnations — the latest being an implementation in java/spring using my jcouchdb library. The design got more and more ambitious over time; so ambitious that it would basically require me to work full-time on it.

The solution was to seriously cut back on my ambitions with this blog and just use one of the available blog engines. This turned out to be wordpress in the end because it seemed like a good fit. The import from my Turbogears blog could be done with a hacky one-liner from the turbogears shell:

"".join(
    map(lambda post : """
        <item>
            <pubDate>%s</pubDate>
            %s
            <title>%s</title>
            <content:encoded>%s</content:encoded>
        </item>\n""" % (
            post.created,
            "".join( map(lambda s: "<category>%s</category>\n" % s,
                             post.tagNames.split(" "))),
            post.name,
            post.text.replace("\n"," ")), posts))

I hope all this will lead to me actually writing stuff in this blog instead of perpetually coding on it.

Implementing stream parsing was really nice and easy thanks to the units test present in svenson. After that, I came upon two ways to generally cut down on memory use. All tokens with fixed values could just have a single instance. The recording of tokens to provide token based look ahead was not really needed in all cases. But how much does that save?

As a test case I wrote a small tool class to generate random, nested JSON datasets, generated two test files of 65kb and 4.5mb size and parsed these with svenson 1.2.8 and what now is svenson 1.3.

Measuring the actual memory usage for these two test files proved to be difficult. Somehow none of the programs I tried seemed to give me the data I wanted. Eclipse TPTP just ignored Strings that were no member of any class but just parameters, making stream and string parsing look exactly the same memory-wise. tijmp and others did not provide the data I wanted at all.

So in the end I wrote a little python script that parses a hprof ASCII output to

• sum up all memory use
• group allocations by class type, but only if the stack trace of it touches svenson
• output the top 10 of those classes and the sums

This provided meaningful data and also showed some points for further improvement. There was a huge number of java.lang.reflect.Method allocations which turned out to be caused by svenson inspecting the target classes for annotations and appropriate methods which was done on a per target basis instead of the better per target class basis.

All in all the memory usage went down quite a bit:

memory usage for different svenson versions, with and without streaming

45% less memory for the small file and 62% for the large file for all allocations. I think that is really good..

Below are some links to the files needed to repeat the benchmarking. The transform hprof script might also prove to be useful for other projects if changed appropriately.

The new jcouchdb release will also use stream parsing.

Links:

• Detailed data: Top 10 memory use by class and sums for all 6 variants
• Python script to transform hprof ASCII output
• Random JSON Generator
• Small JSON test file
• Big JSON test file

edit:
The command to generate the hprof file was something like

java -agentlib:hprof=heap=sites,depth=100,cutoff=0 -cp .. svensonperf.ReadJSONOld big.json