MongoDB

MongoDB (from humongous) is an open source document-oriented database system developed and supported by MongoDB Inc. (formerly 10gen). It is part of the NoSQL family of database systems. Instead of storing data in tables as is done in a "classical" relational database, MongoDB stores structured data as JSON-like documents with dynamic schemas (MongoDB calls the format BSON), making the integration of data in certain types of applications easier and faster.

Installation

MongoDB has been removed from the official repositories due to its re-licensing issues .

Install one of the following for the latest version available:

mongodb^AUR - builds from source, requiring 180GB+ free disk space, and may take several hours to build (i.e. 6.5 hours on older Intel i7 models, 1 hour on a newer i7 9700k with SATA SSD, 1 hour on 32 Xeon cores with high-end NVMe.)
mongodb-bin^AUR - prebuilt MongoDB binary extracted from official MongoDB Ubuntu repository packages. Compilation options used are unknown.

Alternatively, there are older versions of MongoDB available:

Other MongoDB tools can be found packaged as well:

Usage

Start/Enable the daemon.

Note: During the first startup of the mongodb service, it will pre-allocate space, by creating large files (for its journal and other data). This step may take a while, during which the MongoDB shell is unavailable.

To access the MongoDB shell :

$ mongosh

Or, if authentication is configured:

$ mongosh -u userName

Warning: The legacy mongo shell has been deprecated in MongoDB v5.0 and replaced with mongosh. Although it is available in some MongoDB packages, it is highly recommended that you switch it starting in version 5.0.

Configuration

File Format

MongoDB uses a YAML-based configuration file format. See https://docs.mongodb.com/manual/reference/configuration-options/ for available configuration options.

Requiring Authentication

To create a MongoDB user account with administrator access :

Append the following to your .

Restart .

NUMA

Running MongoDB with Non-Uniform Access Memory (NUMA) can significantly impact performance.

To see if your system uses NUMA:

# dmesg | grep -i numa

Also, will show warnings if NUMA is in use and MongoDB is not started through . (The shell will also show this, but only if you do not have authentication enabled.)

If your system uses NUMA, to improve performance, you should make MongoDB start through .

Edit according to the package you installed.

If using , change it from:

ExecStart=/usr/bin/mongod $OPTIONS

To:

ExecStart=/usr/bin/numactl --interleave=all /usr/bin/mongod $OPTIONS

If using mongodb-bin^AUR, change it from:

ExecStart=/usr/bin/mongod --quiet --config /etc/mongodb.conf

To:

ExecStart=/usr/bin/numactl --interleave=all /usr/bin/mongod --quiet --config /etc/mongodb.conf

Zone claim also needs to be disabled, but on arch, defaults to .

Reenable and Restart as needed.

Clean Start and Stop

By default, systemd immediately kills anything after asking it to start or stop, if it has not finished doing so within 90 seconds.

makes systemd wait as long as it takes for MongoDB to start, but mongodb-bin^AUR does not.  Both packages allow systemd to kill MongoDB after it is asked to stop, if it has not finished within 90 seconds.

Large MongoDB databases can take a considerable amount of time to cleanly shut down, especially if swap is being used. (An active 450GB database on a top of the line NVMe with 64GB RAM and 16GB swap can take an hour to shut down.)

By default, MongoDB uses journaling. With journaling, an unclean shutdown should not pose a risk of data loss. But, if not shutdown cleanly, large MongoDB databases can take a considerable amount of time to start back up. In this case, choosing whether to require a clean shutdown is a choice of a slower shutdown versus a slower startup.

To prevent systemd from killing MongoDB after 90 seconds, edit .

To allow MongoDB to cleanly shutdown, append to the section: (On large databases, this may substantially slow down your system shutdown time, but speeds up your next MongoDB start time)

TimeoutStopSec=infinity

If MongoDB needs a long time to start back up, it can be very problematic for systemd to keep killing and restarting it every 90 seconds , so prevents this. If using mongodb-bin^AUR, to make systemd wait as long as it takes for MongoDB to start, append to the section:

TimeoutStartSec=infinity

Troubleshooting

MongoDB will not start

If MongoDB will not start, and you just upgraded to 4.0.6-2+, you probably have a custom . When MongoDB was in the Official repositories, it used an Arch-specific configuration file that used the systemd service type of simple. It now supplies upstream's systemd service and configuration files, which instead use a systemd service type of forking. Pacman will automatically upgrade your systemd service file, but will only automatically upgrade your if you never modified it. In that case, systemd will be expecting mongod to fork, but its configuration file will tell it not to. You need to: switch to the new configuration file installed at , and duplicate changes you made to the old one that you still need, considering the new one is now in the YAML format, and the old one is probably in the MongoDB 2.4 format; or modify your existing one to enable forking. (To continue using the old 2.4 file format instead of YAML, adding should be what is needed.)

Check that is configured to use the correct database location.

Add to the line:

ExecStart=/usr/bin/numactl --interleave=all mongod --quiet --config /etc/mongodb.conf --dbpath /var/lib/mongodb

Check that there is at least 3GB space available for its journal files, otherwise mongodb can fail to start (without issuing a message to the user):

$ df -h /var/lib/mongodb/

Check if the lock file is empty or not:

# ls  -lisa /var/lib/mongodb

If it is, stop . Run a repair on the database, specifying the dbpath (/var/lib/mongodb/ is the default in Arch Linux):

# mongod --dbpath /var/lib/mongodb/ --repair

Upon completion, the dbpath should contain the repaired data files and an empty file.

After running the repair as root, the files will be owned by the root user, whilst Arch Linux runs it under a different user. You will need to use chown to change the ownership of the files back to the correct user. See following link for further details: Further reference

# chown -R mongodb: /var/{log,lib}/mongodb/

Warning about Transparent Huge Pages (THP)

One may want to permanently disable this feature by using a tmpfile:

Use sysctl to disable THP at runtime:

# echo never > /sys/kernel/mm/transparent_hugepage/enabled
# echo never > /sys/kernel/mm/transparent_hugepage/defrag

Warning about Soft rlimits too low

If you are using systemd service, then edit the unit file:

[Service]
# Other directives omitted
# (file size)
LimitFSIZE=infinity
# (cpu time)
LimitCPU=infinity
# (virtual memory size)
LimitAS=infinity
# (locked-in-memory size)
LimitMEMLOCK=infinity
# (open files)
LimitNOFILE=64000
# (processes/threads)
LimitNPROC=64000

See following link for further details: Further reference

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