Runaway memory usage in Sage 5.0?

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Hi,

I am running Sage 5.0 on Windows 7 (as it is the latest Windows version available) and my code is crashing after a couple of hours of computation. Downgrading to Sage 4.8 fixes the problem. I'm not sure exactly where the issue is so I will try to say as much about what I'm doing as possible.

I am using the algorithm described in this paper:

http://www.springerlink.com/content/1...

to build a database of the lattices of order $n$ up to isomorphism. I am up to $n=12$ so far, and my goal is to reach $n=15$. The program works by generating the lattices of order $n+1$ from the lattices of order $n$.

As such, I am using lots of Posets and LatticePosets. Sage should not have to store in memory more than a thousand or so Posets on $\leq 15$ nodes at any point during the code's execution, and should not have to hold much else in memory beyond these posets. My code takes as input the lattices of order $n$ and writes the lattices of order $n+1$ as it generates them to a file. I am running Sage 5.0 in VirtualBox with 4 processors and 1500MB RAM allocated.

My code uses the @parallel decorator on one function. With this, the overall memory usage of my system climbs rapidly from what it was before (X) to X+1500MB, and after a few hours one of the return values from the parallelized function will be 'NO DATA' (instead of what I expected, which is a short list of posets), which tells me something went wrong. If I remove the @parallel decorator and just call my function with single inputs instead of lists of inputs, the memory usage of my system rises rapidly to X+1500MB and after a few hours the entire Sage virtual machine just shuts down.

However, if I downgrade to Sage 4.8, dedicate 4 processors and only 1250MB RAM to Virtualbox, I can use the @parallel decorator and my code will run stably for hours and eventually complete, without my system ever going over X+1000MB memory usage.

Does anyone have any idea what's going on here? Is Sage 5.0 caching all of the lattices of order $n+1$ that I'm generating along the way and eventually running out of memory or something?