[Haskell-cafe] Real-time garbage collection for Haskell

Simon Cranshaw simon.cranshaw at gmail.com
Tue Mar 2 00:22:24 EST 2010


I suspect speed is more important than timing.  In practice I don't mind a
pause for a gc when nothing is happening in the market.  It's when the
market is moving fast that we particularly want to keep our response time
low. Busy times may continue for long periods though and I'm not sure if
being able to defer gc (if that's what you're suggesting) would be possible
for that long.  We are still studying how the gc times are interacting with
our response times and so hopefully I will have a better answer to this
later on.


On Tue, Mar 2, 2010 at 2:06 PM, John Van Enk <vanenkj at gmail.com> wrote:

> Simon,
> Would a more predictable GC or a faster GC be better in your case? (Of
> course, both would be nice.)
> /jve
> On Mon, Mar 1, 2010 at 9:33 PM, Simon Cranshaw <simon.cranshaw at gmail.com>wrote:
>> On Sun, Feb 28, 2010 at 6:06 PM, Pavel Perikov <perikov at gmail.com> wrote:
>>> Did you really seen 100ms pauses?! I never did extensive research on this
>>> but my numbers are rather in microseconds range (below 1ms). What causes
>>> such a long garbage collection? Lots of allocated and long-living objects?
>> I am using an automated options trading system written in Haskell.  I'm
>> more on the business side than the technical side of the issues so I'm not
>> clear on all the details.  I can confirm that without tweaking the RTS
>> settings we were seeing over 100ms GC pauses.  I've mainly been trying to
>> minimise our overall response time and we were able to improve this by
>> increasing the allocation area with -A.  I think this brought GC well under
>> 100ms.  We are still working on analysis of this.
>> I can also confirm, as others seem to have found, that under 6.12 the
>> parallel GC seemed to make things much worse. I am always turning it off
>> with -qg.  If there is a project to improve performance of the GC I could be
>> interested to contribute.
>> Simon Cranshaw
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