Per-class heap plots with py-jstack

Having to profile a webapp that filled the Java Heap, I wrote a simple python module that plots the size of the heap consumed by each class.

It uses the files generated by #jmap -histo $(pidof java); which tracks the memory per-class consumption.

Once you generate your files with something like:

while sleep 5; do
    jmap -histo $(pidof java) > /tmp/histo.$(date %s)

You can load the jplot module included in
Using ipython makes things even easier!

#git clone 
#cd py-jstack;
ipython$ import jplot

Once you loaded the module, you have to list the files to parse
and generate a table containing the classes and their memory occupation in time
for the first 30 greedy classes.

ipython$ files = ! ls /tmp/histo.*
ipython$ table = jplot.jhisto(files, limit=30, delta=False)

What does the `table` dictionary contain? A list of #instance and memory size in time

ipython$ cls = 'java.lang.String'
ipython$ print(table[cls][:10]) 
[(452588.0, 18103520.0), # values in 1st file
 (186198.0, 7447920.0), # values in 2nd file
 (229789.0, 9191560.0), # values in 3rd file
ipython$ memory_for_string = zip(*table[cls])[1]
ipython$ max_memory_for_string = max(memory_for_string)

Using matplotlib we can plot too, and have a glimpse of which class is misbehaving…

ipython$ jplot.plot_classes(table, limit=10)

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