python gc performance in large apps

Chris Lambacher chris at
Mon Oct 24 19:46:40 CEST 2005

A couple of strategic gc.collect() calls can be useful.  You can also tweak
how the garbage collector gets run by changing settings in the gc module.

On Fri, Oct 21, 2005 at 04:13:09PM -0400, Robby Dermody wrote:
> Hey guys (thus begins a book of a post :),
> I'm in the process of writing a commercial VoIP call monitoring and 
> recording application suite in python and pyrex. Basically, this 
> software sits in a VoIP callcenter-type environment (complete with agent 
> phones and VoIP servers), sniffs voice data off of the network, and 
> allows users to listen into calls. It can record calls as well. The 
> project is about a year and 3 months in the making and lately the 
> codebase has stabilized enough to where it can be used by some of our 
> clients. The entire project has about 37,000 lines of python and pyrex 
> code (along with 1-2K lines of unrelated java code).
> Now, some disjointed rambling about the architecture of this software. 
> This software has two long-running server-type components. One 
> component, the "director" application, is written in pure python and 
> makes use of the twisted, nevow, and kinterbasdb libraries (which I 
> realize link to some C extensions). The other component, the 
> "harvester", is a mixture of python and pyrex, and makes use of the 
> twisted library, along with using the C libs libpcap and glib on the 
> pyrex end. Basically, the director is the "master" component. A single 
> director process interacts with users of the system through a web and/or 
> pygtk client application interface and can coordinate 1 to n harvesters 
> spread about the world. The harvester is the "heavy lifter" component 
> that sniffs the network traffic and sifts out the voice and signalling 
> data. It then updates the director of call status changes, and can 
> provide users of the system access to the data. It records the data to 
> disk as well. The scalibility of this thing is really cool: given a 
> single director sitting somewhere coordinating the list of agents, 
> multiple harvester can be placed anywhere there is voice traffic. A user 
> that logs into the director can end up seeing the activity of all of 
> these seperate voice networks presented like a single giant mesh.
> Overall, I have been very pleased with python and the 3rd party 
> libraries that I use (twisted, nevow, kinterbasdb and pygtk). It is a 
> joy to program with, and I think the python community has done a fine 
> job. However, as I have been running the software lately and profiling 
> its memory usage, the one and only Big Problem I have seen is that of 
> the memory usage. Ideally, the server application(s) should be able to 
> run indefinitely, but from the results I'm seeing I will end up 
> exhausting the memory on a 2 GB machine in 2 to 3 days of heavy load.
> Now normally I would not raise up an issue like this on this list, but 
> based on the conversations held on this list lately, and the work done 
> by Evan Jones (, I am led to 
> believe that this memory usage -- while partially due to some probably 
> leaks in my program -- is largely due to the current python gc. I have 
> some graphs I made to show the extent of this memory usage growth:
> The preceding three diagrams are the result of running the 1 director 
> process and 1 harvester process on the same machine for about 48 hours. 
> This is the most basic configuration of this software. I was running 
> this application through /usr/bin/python (CPython) on a Debian 'testing' 
> box running Linux 2.4 with 2GB of memory and Python version 2.3.5. 
> During that time, I gathered the resident and virtual memory size of 
> each component at 120 second intervals. I then imported this data into 
> MINITAB and did some plots. The first one is a graph of the resident 
> (RSS) and virtual memory usage of the two applications. The second one 
> is a zoomed in graph of the director's resident memory usage (complete 
> with a best fit quadratic), and the 3rd one is a zoomed in graph of the 
> harvester's resident memory usage.
> To give you an idea of the network load these apps were undergoing 
> during this sampling time, by the time 48 hours had passed, the 
> harvester had gathered and parsed about 900 million packets. During the 
> day there will be 50-70 agents talking. This number goes to 10-30 at night.
> In the diagrams above, one can see the night-day separation clearly. At 
> night, the memory usage growth seemed to all but stop, but with the 
> increased call volume of the day, it started shooting off again. When I 
> first started gathering this data, I was hoping for a logarithmic curve, 
> but at least after 48 hours, it looks like the usage increase is almost 
> linear. (Although logarithmic may still be the case after it exceeds a 
> gig or two of used memory. :) I'm not sure if this is something that I 
> should expect from the current gc, and when it would stop.
> Now, as I stated above, I am certain that at least some of this 
> increased memory usage is due to either un-collectable objects in the 
> python code, or memory leaks in the pyrex code (where I make some use of 
> malloc/free). I am working on finding and removing these issues, but 
> from what I've seen  with the help of gc UNCOLLECTABLE traces, there are 
> not many un-collectable reference issues at least. Yes, there are some 
> but definitely not enough to justify growth like I am seeing. The pyrex 
> side should not be leaking too much, I'm very good about freeing what I 
> allocate in pyrex/C land. I will be running that linked to a memory leak 
> finding library in the next few days. Past the code reviews I've done, 
> what makes me think that I don't have any *wild* leaks going on at least 
> with the pyrex code is that I am seeing the same type of growth patterns 
> in both apps, and I don't use any pyrex with the director. Yes, the 
> harvester is consuming much more memory, but it also does the majority 
> of the heavy lifting.
> I am alright with the app not freeing all the memory it can between high 
> and low activity times, but what puzzles me is how the memory usage just 
> keeps on growing and growing. Will it ever stop?
> What I would like to know if others on this list have had similar 
> problems with python's gc in long running, larger python applications. 
> Am I crazy or is this a real problem with python's gc itself? If it's a 
> python gc issue, then it's my opinion that we will need to enhance the 
> gc before python can really gain leverage as a language suitable for 
> "enterprise-class" applications. I have surprised many other programmers 
> that I'm writing an application like this in python/pyrex that works 
> just as well and even more efficiently than the C/C++/Java competitors. 
> The only thing I have left to show is that the app lasts as long between 
> restarts. ;)
> Robby
> -- 

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