important config note on running MongoDB in production on Linux

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dwight_10gen

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Jun 29, 2011, 1:07:12 PM6/29/11
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The mongod process uses a thread per connection. Each thread has a
stack. Typically on Linux the default stack size is 8MB. That's a
lot of memory if you have 1,000 or 10,000 connections -- enough that
it may cause your server to become very slow. Linux seems to not like
to swap out the unused portion of the stacks, despite mongod typically
using a small fraction of that 8MB stack space.

To check your number of connections, run in the mongo shell:

db.serverStatus().connections

If it is a small number, you are fine. If a larger number, we
recommend you lower the default stack size using ulimit. The syntax
is:

ulimit -s 1024

which will set the stack size to 1MB instead of 8MB.

In MongoDB v2.0 this will happen automatically.

Mike K

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Jun 29, 2011, 2:46:06 PM6/29/11
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Thanks Dwight!

Do you (or anyone else) know the equivalent to put into /etc/sysctl.conf so that this limit persists across reboots?

Thanks,
Mike

Zack Radick

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Jun 29, 2011, 3:00:59 PM6/29/11
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For Ubuntu you can edit /etc/security/limits.conf.
--Zack

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axlfu

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Jun 29, 2011, 8:11:11 PM6/29/11
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Do I have to restart mongod?
If not , what about the old collections' stack size, are they still
8m?

axlfu

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Jun 29, 2011, 8:53:55 PM6/29/11
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How to Estimate the stack size,What are included?

On Jun 30, 1:07 am, dwight_10gen <dwi...@10gen.com> wrote:

Eliot Horowitz

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Jun 29, 2011, 9:39:29 PM6/29/11
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stack size is a linux process wide setting, not collection.
After you change, you have to restart mongod.

You can find the current by doing "ulimit -s"

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付玉

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Jun 29, 2011, 10:01:41 PM6/29/11
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How do I know if my set is ok?
Is this just a buffer?

2011/6/30 Eliot Horowitz <elioth...@gmail.com>

Dwight Merriman

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Jun 30, 2011, 12:37:52 AM6/30/11
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yes a buffer, the thread's stack, for each thread -- there is a thread per connection.

Sergei Tulentsev

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Jun 30, 2011, 11:39:18 AM6/30/11
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> db.serverStatus().connections
{ "current" : 29, "available" : 790 }

Do I have 29 connections (with their stacks) and I can create 790 more?
Or those 790 are just sitting idle?
Best regards,
Sergei Tulentsev

Nat

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Jun 30, 2011, 12:15:24 PM6/30/11
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That's right. It means you can create 790 more. They're not idle connections.
From: Sergei Tulentsev <sergei.t...@gmail.com>
Date: Thu, 30 Jun 2011 19:39:18 +0400
Subject: Re: [mongodb-user] Re: important config note on running MongoDB in production on Linux
Message has been deleted

mathias

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Jul 29, 2011, 11:52:06 AM7/29/11
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On Jun 29, 8:11 pm, axlfu <freesearc...@gmail.com> wrote:
> Do I have to restart mongod?
> If not , what about the old collections' stack size, are they still
> 8m?


This is about connections, not collections.

Eliot Horowitz

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Jul 12, 2012, 12:10:45 AM7/12/12
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Right, that's normal.
So since its min(1,10) it'll be 1, which is good.

On Thu, Jul 12, 2012 at 12:07 AM, gmz <gen...@gmail.com> wrote:
> hi
> I am using mongodb 2.0.4, as "2.0 Release Notes" saying the default stack
> size would be "the lesser of the system setting or 1MB".
> but as follows, I found the stack size is 10240K in the process limits file,
> is it true?
>
> Production: [mba@mg3sh] ~$ ps aux|grep mongo
> mba 15594 0.1 29.5 80910156 14623684 ? Sl Apr09 206:15
> ./bin/mongod --port 27038 --replSet shard03/10.16.1.240:27038 --fork
> --dbpath /data1/mba-data/shard03/ --oplogSize 20480 --logpath
> /data1/mba-logs/shard03/mongod.log --logappend
>
> Production: [mba@mg3sh] ~$ ulimit -a|grep stack
> stack size (kbytes, -s) 10240
> Production: [mba@mg3sh] ~$ cat /proc/15594/limits |grep stack
> Max stack size 10485760 unlimited bytes
> Production: [mba@mg3sh] ~$
>
> gmz
> 7/12 2012
>
> 在 2011年6月30日星期四UTC+8上午1时07分12秒,dwight_10gen写道:
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gmz

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Jul 12, 2012, 12:28:27 AM7/12/12
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but I see the stack size is 10M in the process limits file, as follows. why?

Production: [mba@mg3sh] ~$ cat /proc/15594/limits |grep stack
Max stack size            10485760             unlimited            bytes     
10485760 bytes is 10M.

在 2012年7月12日星期四UTC+8下午12时10分45秒,Eliot Horowitz写道:

Eliot Horowitz

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Jul 12, 2012, 12:29:59 AM7/12/12
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Thats the system setting.
mongo can control it at thread creation time.
>> > mongodb-user...@googlegroups.com
>> > See also the IRC channel -- freenode.net#mongodb
>
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gmz

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Jul 12, 2012, 12:42:54 AM7/12/12
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I see, thanks.

在 2012年7月12日星期四UTC+8下午12时29分59秒,Eliot Horowitz写道:
>> > See also the IRC channel -- freenode.net#mongodb
>
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Rendy Bambang Junior

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Sep 16, 2014, 11:11:04 PM9/16/14
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 Hi Dwight,

Does it still apply now? I noticed that it is not there as recommendation or notes in current mongodb manual http://docs.mongodb.org/manual/reference/ulimit/

I find another blog about this matter https://blog.serverdensity.com/mongodb-connection-overhead/, however it is published at 2011 as well, so I am not really sure whether it still applies now.

Thanks!
Rendy

Stephen Steneker

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Sep 16, 2014, 11:16:04 PM9/16/14
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On Wednesday, 17 September 2014 13:11:04 UTC+10, Rendy Bambang Junior wrote:
Does it still apply now? I noticed that it is not there as recommendation or notes in current mongodb manual http://docs.mongodb.org/manual/reference/ulimit/

I find another blog about this matter https://blog.serverdensity.com/mongodb-connection-overhead/, however it is published at 2011 as well, so I am not really sure whether it still applies now.

Hi Rendy,

As noted in the original thread you replied to (from 2011) the stack size limit was changed for MongoDB 2.0 to the lesser of the system setting or 1MB:
 http://docs.mongodb.org/manual/release-notes/2.0/#default-stack-size

Regards,
Stephen
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