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?.

Solution 1

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.
  dbPath: /var/lib/mongodb
    enabled: true
        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

Solution 2

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

Solution 3

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 ...

Solution 4

You can limit mongod process usage using cgroups on Linux.

Using cgroups, our task can be accomplished in a few easy steps.

  1. 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)

  2. Specify how much memory will be available for this group:

    echo 16G > /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)

  3. Now, it will be a good idea to drop pages already stayed in cache:

    sync; echo 3 > /proc/sys/vm/drop_caches
  4. 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

Solution 5

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.

Solution 6

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 -

    configString : cache_size=345M

Source - https://jira.mongodb.org/browse/SERVER-22274

Solution 7

mongod --wiredTigerCacheSizeGB 2 xx

Solution 8

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

Solution 9

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.

Solution 10

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/

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'

Solution 11

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;


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:          26695              Spans in use
MALLOC:             22              Thread heaps in use
MALLOC:           4096              Tcmalloc page size

Solution 12

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 } )"

Solution 13

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.

[email protected]hongse:~$ free -m
             total       used       free     shared    buffers     cached
Mem:          3952       3667        284          0        617        514
-/+ buffers/cache:       2535       1416
Swap:            0          0          0
[email protected]hongse:~$ sudo su
[email protected]hongse:/home/ubuntu# sync; echo 3 > /proc/sys/vm/drop_caches
[email protected]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

Solution 14

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.

  1. Create you mongod.conf file:
# Limits cache storage
         cacheSizeGB: 1 # Set the size you want
  1. 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
  2. Alternatively you could use a docker-compose.yml file:
version: '3'

        image: mongo:4.2
        # Sets the config file
        command: --config /etc/mongo/mongod.conf
            - ./config/mongo/mongod.conf:/etc/mongo/mongod.conf
        # Others settings...