Re: How to manage growing memory with Rainbows!

[Eric Wong <normalperson-rMlxZR9MS24@public.gmane.org>]

Claudio Poli <claudio-3HQ/CcOImoi171pxa8y+qA@public.gmane.org> wrote:
> My only concern is the growing memory, as we know Ruby does not really
> do a good job at it (at least for me, even with all the tweaks in the
> world) and I need to find a good way to kill a process and restart
> since we are running in a memory-constrained environment.

I'm curious, what tweaks did you try?

What kind of workload are you running? (many disk writes at all?)
Which version of Ruby are you using?
Are you counting VMSize or RSS?
Are you on 64-bit?

Fwiw, virtual memory usage is very high on 64-bit Linux on newer
versions of glibc, but mostly harmless since the memory isn't actually
used (address space is nearly unlimited).

You can try MALLOC_ARENA_MAX_=1 to limit the number of arenas if you
want.  That might reduce fragmentation since the GVL in MRI means
it's unlikely to hit malloc lock contention (glibc uses multiple
malloc arenas to avoid contention by default).

> What are you using currently? Monit, OobGC? The good thing about the
> gem above is that it will kill the Unicorn worker only after the last
> requests has been performed and with easy adjustable thresholds.

OobGC is absolutely not recommended for Rainbows! (or anything doing
persistent connections or simultaneous clients within a process)

However, you can safely send SIGQUIT to any Rainbows! worker (bypassing
master) whenever you feel memory usage is high, master will restart it.

You can just put a simple counter in middleware to do it, something
like this:

# nr is initialized to a number of your choice elsewhere

	nr -= 1
	if nr < 0
	  Process.kill(:QUIT, $$)
	end

> Can you point me into the right direction here? Thanks!

The best solution is to fix your code/gems/Ruby :)

I report and fix all the memory leaks I can find in gems+MRI.

One thing to avoid is allocating too much memory in the first place
(always use LIMIT in SQL SELECT statements, read files in smaller
chunks, etc).  It really takes only one poorly thought-out line of
code to either OOM or cause a swap storm.

I haven't hit one of these problems in a while, but check out
commit f95113402b7239f225282806673e1b6424522b18 in
git://github.com/rack/rack.git for an example of how IO#gets
can ruin your app.
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