Is there any option to limit mongodb memory usage

Question

I am using Mongo-DBv1 8 1  My server memory is 4GB but Mongo-DB is utilizing more than 3GB  Is there memory limitation option in Mongo-DB

User · Answer

There is no reason to limit MongoDB cache as by default the mongod process will take 1/2 of the memory on the machine and no more. The default storage engine is WiredTiger. "With WiredTiger, MongoDB utilizes both the WiredTiger internal cache and the filesystem cache."

You are probably looking at top and assuming that Mongo is using all the memory on your machine. That is virtual memory. Use free -m:

              total        used        free      shared  buff/cache   available
Mem:           7982        1487        5601           8         893        6204
Swap:             0           0           0

Only when the available metric goes to zero is your computer swapping memory out to disk. In that case your database is too large for your machine. Add another mongodb instance to your cluster.

Use these two commands in the mongod console to get information about how much virtual and physical memory Mongodb is using:

var mem = db.serverStatus().tcmalloc;

mem.tcmalloc.formattedString

------------------------------------------------
MALLOC:      360509952 (  343.8 MiB) Bytes in use by application
MALLOC: +    477704192 (  455.6 MiB) Bytes in page heap freelist
MALLOC: +     33152680 (   31.6 MiB) Bytes in central cache freelist
MALLOC: +      2684032 (    2.6 MiB) Bytes in transfer cache freelist
MALLOC: +      3508952 (    3.3 MiB) Bytes in thread cache freelists
MALLOC: +      6349056 (    6.1 MiB) Bytes in malloc metadata
MALLOC:   ------------
MALLOC: =    883908864 (  843.0 MiB) Actual memory used (physical + swap)
MALLOC: +     33611776 (   32.1 MiB) Bytes released to OS (aka unmapped)
MALLOC:   ------------
MALLOC: =    917520640 (  875.0 MiB) Virtual address space used
MALLOC:
MALLOC:          26695              Spans in use
MALLOC:             22              Thread heaps in use
MALLOC:           4096              Tcmalloc page size

User · Answer

mongod --wiredTigerCacheSizeGB 2 xx

User · Answer

For Windows it seems possible to control the amount of memory MongoDB uses  see this tutorial at Captain Codeman   Limit MongoDB memory use on Windows without Virtualization

User · Answer

This question has been asked a couple times       See this related question answer  quoted below      how to release the caching which is used by Mongodb     MongoDB will  at least seem  to use up a lot of available memory  but it actually leaves it up to the OS s VMM to tell it to release the memory  see Caching in the MongoDB docs     You should be able to release any and all memory by restarting MongoDB   However  to some extent MongoDB isn t really  using  the memory    For example from the MongoDB docs Checking Server Memory Usage         Depending on the platform you may see   the mapped files as memory in the   process  but this is not strictly   correct  Unix top may show way more   memory for mongod than is really   appropriate  The Operating System  the   virtual memory manager specifically    depending on OS  manages the memory   where the  Memory Mapped Files    reside  This number is usually shown   in a program like  free -lmt        It is called  cached  memory    MongoDB uses the LRU  Least Recently Used  cache algorithm to determine which  pages  to release  you will find some more information in these two questions       MongoDB limit memory  MongoDB index RAM relationship Mongod start with memory limit  You can t

User · Answer

If you are running MongoDB 3 2 or later version  you can limit the wiredTiger cache as mentioned above   In  etc mongod conf add the wiredTiger part        Where and how to store data  storage    dbPath   var lib mongodb   journal      enabled  true   wiredTiger      engineConfig          cacheSizeGB  1       This will limit the cache size to 1GB  more info in Doc  This solved the issue for me  running ubuntu 16 04 and mongoDB 3 2  PS  After changing the config  restart the mongo daemon     sudo service mongod restart    check the status   sudo service mongod status

User · Answer

Starting in 3 2  MongoDB uses the WiredTiger as the default storage engine  Previous versions used the MMAPv1 as the default storage engine    With WiredTiger  MongoDB utilizes both the WiredTiger internal cache and the filesystem cache  In MongoDB 3 2  the WiredTiger internal cache  by default  will use the larger of either  60  of RAM minus 1 GB  or 1 GB  For systems with up to 10 GB of RAM  the new default setting is less than or equal to the 3 0 default setting  For MongoDB 3 0  the WiredTiger internal cache uses either 1 GB or half of the installed physical RAM  whichever is larger   For systems with more than 10 GB of RAM  the new default setting is greater than the 3 0 setting      to limit the wiredTriggered Cache Add following line to  config file    wiredTigerCacheSizeGB   1

User · Answer

One thing you can limit is the amount of memory mongodb uses while building indexes  This is set using the maxIndexBuildMemoryUsageMegabytes setting  An example of how its set is below    mongo --eval  db adminCommand    setParameter  1  maxIndexBuildMemoryUsageMegabytes  70000

User · Answer

Not really  there are a couple of tricks to limit memory  like on Windows you can use the Windows System Resource Manager  WSRM   but generally Mongo works best on a dedicated server when it s free to use memory without much contention with other systems   Although the operating system will try to allocate memory to other processes as they need it  in practice this can lead to performance issues if other systems have high memory requirements too   If you really need to limit memory  and only have a single server  then your best bet is virtualization

User · Answer

If you re using Docker  reading the Docker image documentation  in the Setting WiredTiger cache size limits section  I found out that they set the default to consume all available memory regardless of memory limits you may have imposed on the container  so you would have to limit the RAM usage directly from the DB configuration   Create you mongod conf file     Limits cache storage storage     wiredTiger        engineConfig           cacheSizeGB  1   Set the size you want   Now you can assign that config file to the container  docker run --name mongo-container -v  path to mongod conf  etc mongo mongod conf -d mongo --config  etc mongo mongod conf Alternatively you could use a docker-compose yml file   version   3   services      mongo          image  mongo 4 2           Sets the config file         command  --config  etc mongo mongod conf         volumes              -   config mongo mongod conf  etc mongo mongod conf           Others settings

User · Answer

this worked for me on an AWS instance  to at least clear the cached memory mongo was using  after this you can see how your settings have had effect   ubuntu hongse    free -m              total       used       free     shared    buffers     cached Mem           3952       3667        284          0        617        514 -   buffers cache        2535       1416 Swap             0          0          0 ubuntu hongse    sudo su root hongse  home ubuntu  sync  echo 3  gt   proc sys vm drop caches root hongse  home ubuntu  free -m              total       used       free     shared    buffers     cached Mem           3952       2269       1682          0          1         42 -   buffers cache        2225       1726 Swap             0          0          0

User · Answer

You can limit mongod process usage using cgroups on Linux   Using cgroups  our task can be accomplished in a few easy steps    Create control group    cgcreate -g memory DBLimitedGroup     make sure that cgroups binaries installed on your system  consult your favorite Linux distribution manual for how to do that  Specify how much memory will be available for this group   echo 16G  gt   sys fs cgroup memory DBLimitedGroup memory limit in bytes   This command limits memory to 16G  good thing this limits the memory for both malloc allocations and OS cache  Now  it will be a good idea to drop pages already stayed in cache   sync  echo 3  gt   proc sys vm drop caches  And finally assign a server to created control group   cgclassify -g memory DBLimitedGroup   pidof mongod     This will assign a running mongod process to a group limited by only 16GB memory    source  Using Cgroups to Limit MySQL and MongoDB memory usage

User · Answer

I don t think you can configure how much memory MongoDB uses  but that s OK  read below    To quote from the official source      Virtual memory size and resident size will appear to be very large for the mongod process   This is benign  virtual memory space will be just larger than the size of the datafiles open and mapped  resident size will vary depending on the amount of memory not used by other processes on the machine    In other words  Mongo will let other programs use memory if they ask for it

User · Answer

Adding to the top voted answer  in case you are on a low memory machine and want to configure the wiredTigerCache in MBs instead of whole number GBs  use this -   storage   wiredTiger    engineConfig      configString   cache size 345M   Source - https   jira mongodb org browse SERVER-22274

User · Answer

This can be done with cgroups  by combining knowledge from these two articles  https   www percona com blog 2015 07 01 using-cgroups-to-limit-mysql-and-mongodb-memory-usage  http   frank2 net cgroups-ubuntu-14-04   You can find here a small shell script which will create config and init files for Ubuntu 14 04  http   brainsuckerna blogspot com by 2016 05 limiting-mongodb-memory-usage-with html  Just like that   sudo bash -c  curl -o- http   brains by misc mongodb memory limit ubuntu1404 sh   bash

[mongodb] Is there any option to limit mongodb memory usage?

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