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Message from discussion Memory-effective queue handling
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Attila Rajmund Nohl  
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 More options Jul 25 2012, 9:44 am
From: Attila Rajmund Nohl <attila.r.n...@gmail.com>
Date: Wed, 25 Jul 2012 15:44:35 +0200
Local: Wed, Jul 25 2012 9:44 am
Subject: Re: [erlang-questions] Memory-effective queue handling
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2012/7/25 Richard Carlsson <carlsson.rich...@gmail.com>:
[...]

> You'd only run out of space if the queue is so long that you don't have
> memory enough to call lists:reverse() on the current in-half of the queue
> (and after that, the old queue will immediately become garbage). Can that
> really be the case?

It might happen. According to the crash dump the process in question uses
Stack+heap: 228065700

words of memory. I store a tuple of bigint and a small integer in the
queue, and the queue is essentially a list (actually two lists, but
doesn't matter), so one entry in the queue costs 2+3(?)+1+1=7 words.
The process has some other stuff in its state, but that should be
negligible. The erlang VM run for less than 13 hours. If I calculate
correctly, this means that there should be around 600 events per
second though 13 hours to reach this amount of memory. After some
internal conversation I think it is possible that due to an unrelated
bug I do get this much events.

> But you should be able to improve the behaviour of the above code by using
> queue:peek_r(Q) instead of queue:out(Q), and then call queue:drop_r(Q) in
> the second case clause only, so no rewriting of the queue representation is
> done unless necessary.

Thanks.
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