256kB stack size ok?

[MK <mk...@cognitivedissonance.ca>]

Does anyone have an idea of what a safe minimum stack size is for
couch?   I have it on a linux openVZ slice, and OVZ counts something
called "allocated memory" which AFAICT most closely resembles the
"writable/private" stat found with pmap -d.

At start-up, beam.smp has 12 threads; with a default stack of 8MB each,
that's 96MB.  After a while it grows to 25 threads and about a 1/4 GB
of "allocated memory".    I'd expect that to be the minimum using a
default stack size.

So I cut the system stack size to 256kB, which reduced my overall mem
usage by more than half,  and WRT to couch, about 90%.  Everything
seems okay, but am totally unfamiliar with erlang, and was just
wondering if someone in the know here can provide some reassurance.

-- 
"Enthusiasm is not the enemy of the intellect." (said of Irving Howe)
"The angel of history[...]is turned toward the past." (Walter Benjamin)

Re: 256kB stack size ok?

[MK <mk...@cognitivedissonance.ca>]

On Wed, 22 Jun 2011 14:34:25 -0700
Randall Leeds <ra...@gmail.com> wrote:
> On Wed, Jun 22, 2011 at 05:50, MK <mk...@cognitivedissonance.ca> wrote:
> > Does anyone have an idea of what a safe minimum stack size is for
> > couch? 
> This is an excellent question and it'd be really cool to hear some
> good thoughts on this.
> 
> In particular, I'm not sure what (from a libc perspective) is stack
> allocation and what is heap allocation in the Erlang runtime.
> Looking around quickly it's not easy to find documentation on BEAM
> itself (Bogdan/Björn's Erlang Abstract Machine).

I did not even know that's what it is, thanks ;)

> Perhaps there are some more basic questions that we could cross-post
> to erlang?

I don't think you could simplify it beyond "Do you know how big a stack
this application needs?"  256kB seems like a lot to me, I have no idea
why someone would need the linux default of 8MB.  

You can limit thread stack size internally, at least with pthreads.  I
noticed when doing this on the server that nodejs (or the "libeio"
it includes/uses) does that -- it has a very small "allocated memory"
footprint by default.  Kind of a lesson there for developers perhaps.
That beam thing is just colossal, at least on linux.

-- 
"Enthusiasm is not the enemy of the intellect." (said of Irving Howe)
"The angel of history[...]is turned toward the past." (Walter Benjamin)

Re: 256kB stack size ok?

[Randall Leeds <ra...@gmail.com>]

On Wed, Jun 22, 2011 at 05:50, MK <mk...@cognitivedissonance.ca> wrote:
> Does anyone have an idea of what a safe minimum stack size is for
> couch?   I have it on a linux openVZ slice, and OVZ counts something
> called "allocated memory" which AFAICT most closely resembles the
> "writable/private" stat found with pmap -d.
>
> At start-up, beam.smp has 12 threads; with a default stack of 8MB each,
> that's 96MB.  After a while it grows to 25 threads and about a 1/4 GB
> of "allocated memory".    I'd expect that to be the minimum using a
> default stack size.
>
> So I cut the system stack size to 256kB, which reduced my overall mem
> usage by more than half,  and WRT to couch, about 90%.  Everything
> seems okay, but am totally unfamiliar with erlang, and was just
> wondering if someone in the know here can provide some reassurance.
>

This is an excellent question and it'd be really cool to hear some
good thoughts on this.

In particular, I'm not sure what (from a libc perspective) is stack
allocation and what is heap allocation in the Erlang runtime.
Looking around quickly it's not easy to find documentation on BEAM
itself (Bogdan/Björn's Erlang Abstract Machine).
I realize I don't even know if it's stack-based, what kind of
registers it has, etc...

Perhaps there are some more basic questions that we could cross-post to erlang?