This page details system configurations that affect MongoDB, especially in production.
MongoDB Management Service (MMS), a hosted service, and Ops Manager, an on-premise solution, provide monitoring, backup, and automation of MongoDB instances. See the MMS documentation and Ops Manager documentation for more information.
Changed in version 3.0: MongoDB includes support for two storage engines: MMAPv1, the storage engine available in previous versions of MongoDB, and WiredTiger. MongoDB uses the MMAPv1 engine by default.
The files in the dbPath directory must correspond to the configured storage engine. mongod will not start if dbPath contains data files created by a storage engine other than the one specified by --storageEngine.
MongoDB distributions are currently available for Mac OS X, Linux, Windows Server 2008 R2 64bit, Windows 7 (64 bit), Windows Vista, and Solaris. The MongoDB distribution for Solaris does not include support for the WiredTiger storage engine.
For a full list of the recommended operating systems for production deployments, see: Recommended Operating Systems for Production Deployments.
Use the Latest Stable Packages¶
Be sure you have the latest stable release.
Changed in version 3.0: Beginning with MongoDB 3.0, MMAPv1 provides collection-level locking: All collections have a unique readers-writer lock that allows multiple clients to modify documents in different collections at the same time.
For MongoDB versions 2.2 through 2.6 series, each database has a readers-writer lock that allows concurrent read access to a database, but gives exclusive access to a single write operation per database. See the Concurrency page for more information. In earlier versions of MongoDB, all write operations contended for a single readers-writer lock for the entire mongod instance.
WiredTiger supports concurrent access by readers and writers to the documents in a collection. Clients can read documents while write operations are in progress, and multiple threads can modify different documents in a collection at the same time.
MongoDB uses write ahead logging to an on-disk journal. Journaling guarantees that MongoDB can quickly recover write operations that were not written to data files in cases where mongod terminated as a result of a crash or other serious failure.
Write concern describes the guarantee that MongoDB provides when reporting on the success of a write operation. The strength of the write concerns determine the level of guarantee. When inserts, updates and deletes have a weak write concern, write operations return quickly. In some failure cases, write operations issued with weak write concerns may not persist. With stronger write concerns, clients wait after sending a write operation for MongoDB to confirm the write operations.
MongoDB provides different levels of write concern to better address the specific needs of applications. Clients may adjust write concern to ensure that the most important operations persist successfully to an entire MongoDB deployment. For other less critical operations, clients can adjust the write concern to ensure faster performance rather than ensure persistence to the entire deployment.
See the Write Concern document for more information about choosing an appropriate write concern level for your deployment.
Use Trusted Networking Environments¶
Always run MongoDB in a trusted environment, with network rules that prevent access from all unknown machines, systems, and networks. As with any sensitive system that is dependent on network access, your MongoDB deployment should only be accessible to specific systems that require access, such as application servers, monitoring services, and other MongoDB components.
By default, authorization is not enabled, and mongod assumes a trusted environment. Enable authorization mode as needed. For more information on authentication mechanisms supported in MongoDB as well as authorization in MongoDB, see Authentication and Authorization.
For additional information and considerations on security, refer to the documents in the Security Section, specifically:
For Windows users, consider the Windows Server Technet Article on TCP Configuration when deploying MongoDB on Windows.
Disable HTTP Interfaces¶
MongoDB provides interfaces to check the status of the server and, optionally, run queries on it, over HTTP. In production environments, disable the HTTP interfaces.
Manage Connection Pool Sizes¶
To avoid overloading the connection resources of a single mongod or mongos instance, ensure that clients maintain reasonable connection pool sizes. Adjust the connection pool size to suit your use case, beginning at 110-115% of the typical number of concurrent database requests.
See also Allocate Sufficient RAM and CPU.
MongoDB is designed specifically with commodity hardware in mind and has few hardware requirements or limitations. MongoDB’s core components run on little-endian hardware, primarily x86/x86_64 processors. Client libraries (i.e. drivers) can run on big or little endian systems.
Allocate Sufficient RAM and CPU¶
The MMAPv1 storage engine is not CPU bound due to its concurrency model. As such, increasing the number of cores can help but does not provide significant return.
Increasing the amount of RAM accessible to MongoDB may help reduce the frequency of page faults.
The WiredTiger storage engine is CPU bound. Specifically, the total number of active threads (i.e. concurrent operations) relative to the number of CPUs can impact performance:
- Throughput increases as the number of concurrent active operations increases up to the number of CPUs.
- Throughput decreases as the number of concurrent active operations exceeds the number of CPUs by some threshold amount.
The threshold amount depends on your application. You can determine the optimum number of concurrent active operations for your application by experimenting and measuring throughput. The output from mongostat provides statistics on the number of active reads/writes in the (ar|aw) column.
WiredTiger’s default configuration will use either 1GB or half of the installed physical RAM for cache, whichever is larger. This size is tunable through the storage.wiredTiger.engineConfig.cacheSizeGB setting, and should be large enough to hold your entire working set.
The default storage.wiredTiger.engineConfig.cacheSizeGB setting assumes that there is a single mongod instance per node. If a single node contains multiple instances, then you should adjust the storage.wiredTiger.engineConfig.cacheSizeGB setting to accommodate the working set as well as the other mongod instances.
If you run mongod in a container (e.g. lxc, cgroups, Docker, etc.) that does not have access to all of the RAM available in a system, you must set the storage.wiredTiger.engineConfig.cacheSizeGB to a value less than the amount of RAM available in the container. The exact amount depends on the other processes running in the container.
Use Solid State Disks (SSDs)¶
MongoDB has good results and a good price-performance ratio with SATA SSD (Solid State Disk).
Use SSD if available and economical. Spinning disks can be performant, but SSDs’ capacity for random I/O operations works well with the update model of MMAPv1.
Commodity (SATA) spinning drives are often a good option, as the random I/O performance increase with more expensive spinning drives is not that dramatic (only on the order of 2x). Using SSDs or increasing RAM may be more effective in increasing I/O throughput.
MongoDB and NUMA Hardware¶
Running MongoDB on a system with Non-Uniform Access Memory (NUMA) can cause a number of operational problems, including slow performance for periods of time and high system process usage.
When running MongoDB servers and clients on NUMA hardware, you should configure a memory interleave policy so that the host behaves in a non-NUMA fashion. MongoDB checks NUMA settings on start up when deployed on Linux (since version 2.0) and Windows (since version 2.6) machines. If the NUMA configuration may degrade performance, MongoDB prints a warning.
See The MySQL “swap insanity” problem and the effects of NUMA post, which describes the effects of NUMA on databases. This blog post addresses the impact of NUMA for MySQL, but the issues for MongoDB are similar. The post introduces NUMA and its goals, and illustrates how these goals are not compatible with production databases.
Configuring NUMA on Windows¶
On Windows, memory interleaving must be enabled through the machine’s BIOS. Please consult your system documentation for details.
Configuring NUMA on Linux¶
numactl --interleave=all <path>
where <path> is the path to the program you are starting. Then, disable zone reclaim in the proc settings using the following command:
echo 0 > /proc/sys/vm/zone_reclaim_mode
To fully disable NUMA behavior, you must perform both operations. For more information, see the Documentation for /proc/sys/vm/*.
Disk and Storage Systems¶
Assign swap space for your systems. Allocating swap space can avoid issues with memory contention and can prevent the OOM Killer on Linux systems from killing mongod.
For the MMAPv1 storage engine, the method mongod uses to map files to memory ensures that the operating system will never store MongoDB data in swap space. On Windows systems, using MMAPv1 requires extra swap space due to commitment limits. For details, see MongoDB on Windows.
The WiredTiger storage engine also ensures that the operating system does not store MongoDB data in swap space.
Most MongoDB deployments should use disks backed by RAID-10.
RAID-5 and RAID-6 do not typically provide sufficient performance to support a MongoDB deployment.
Avoid RAID-0 with MongoDB deployments. While RAID-0 provides good write performance, it also provides limited availability and can lead to reduced performance on read operations, particularly when using Amazon’s EBS volumes.
With the MMAPv1 storage engine, the Network File System protocol (NFS) is not recommended as you may see performance problems when both the data files and the journal files are hosted on NFS. You may experience better performance if you place the journal on local or iscsi volumes.
The WiredTiger storage engine does not experience performance issues with NFS.
If you decide to use NFS, add the following NFS options to your /etc/fstab file: bg, nolock, and noatime.
Separate Components onto Different Storage Devices¶
For improved performance, consider separating your database’s data, journal, and logs onto different storage devices, based on your application’s access and write pattern.
For the WiredTiger storage engine, you can also store the indexes on a different storage device. See storage.wiredTiger.engineConfig.directoryForIndexes.
Using different storage devices will affect your ability to create snapshot-style backups of your data, since the files will be on different devices and volumes.
Scheduling for Virtual Devices¶
Local block devices attached to virtual machine instances via the hypervisor should use a noop scheduler for best performance. The noop scheduler allows the operating system to defer I/O scheduling to the underlying hypervisor.
WiredTiger can compress collection data using either snappy or zlib compression library. snappy provides a lower compression rate but has little performance cost, whereas zlib provides better compression rate but has a higher performance cost.
By default, WiredTiger uses snappy compression library. To change the compression setting, see storage.wiredTiger.collectionConfig.blockCompressor.
WiredTiger uses prefix compression on all indexes by default.
Platform Specific Considerations¶
MongoDB uses the GNU C Library (glibc) if available on a system. MongoDB requires version at least glibc-2.12-1.2.el6 to avoid a known bug with earlier versions. For best results use at least version 2.13.
MongoDB on Linux¶
Kernel and File Systems¶
When running MongoDB in production on Linux, it is recommended that you use Linux kernel version 2.6.36 or later.
With the MMAPv1 storage engine, MongoDB preallocates its database files before using them and often creates large files. As such, you should use the Ext4 and XFS file systems:
In general, if you use the Ext4 file system, use at least version 2.6.23 of the Linux Kernel.
In general, if you use the XFS file system, use at least version 2.6.25 of the Linux Kernel.
Some Linux distributions require different versions of the kernel to support using ext4 and/or xfs:
Linux Distribution Filesystem Kernel Version CentOS 5.5 ext4, xfs 2.6.18-194.el5 CentOS 5.6 ext4, xfs 2.6.18-3.0.el5 CentOS 5.8 ext4, xfs 2.6.18-308.8.2.el5 CentOS 6.1 ext4, xfs 2.6.32-131.0.15.el6.x86_64 RHEL 5.6 ext4 2.6.18-3.0 RHEL 6.0 xfs 2.6.32-71 Ubuntu 10.04.4 LTS ext4, xfs 2.6.32-38-server Amazon Linux AMI release 2012.03 ext4 3.2.12-3.2.4.amzn1.x86_64
fsync() on Directories¶
MongoDB requires a filesystem that supports fsync() on directories. For example, HGFS and Virtual Box’s shared folders do not support this operation.
For the MMAPv1 storage engine and the WiredTiger storage engines, consider the following recommendations:
- Turn off atime for the storage volume containing the database files.
- Set the file descriptor limit, -n, and the user process limit (ulimit), -u, above 20,000, according to the suggestions in the ulimit document. A low ulimit will affect MongoDB when under heavy use and can produce errors and lead to failed connections to MongoDB processes and loss of service.
- Disable Transparent Huge Pages, as MongoDB performs better with normal (4096 bytes) virtual memory pages. See Transparent Huge Pages Settings.
- Disable NUMA in your BIOS. If that is not possible, see MongoDB on NUMA Hardware.
For the MMAPv1 storage engine:
Ensure that readahead settings for the block devices that store the database files are appropriate. For random access use patterns, set low readahead values. A readahead of 32 (16kb) often works well.
For a standard block device, you can run sudo blockdev --report to get the readahead settings and sudo blockdev --setra <value> <device> to change the readahead settings. Refer to your specific operating system manual for more information.
For all MongoDB deployments:
- Use the Network Time Protocol (NTP) to synchronize time among your hosts. This is especially important in sharded clusters.
MongoDB and SSL Libraries¶
On Linux platforms, you may observe one of the following statements in the MongoDB log:
<path to SSL libs>/libssl.so.<version>: no version information available (required by /usr/bin/mongod) <path to SSL libs>/libcrypto.so.<version>: no version information available (required by /usr/bin/mongod)
These warnings indicate that the system’s SSL libraries are different from the SSL libraries that the mongod was compiled against. Typically these messages do not require intervention; however, you can use the following operations to determine the symbol versions that mongod expects:
objdump -T <path to mongod>/mongod | grep " SSL_" objdump -T <path to mongod>/mongod | grep " CRYPTO_"
These operations will return output that resembles one the of the following lines:
0000000000000000 DF *UND* 0000000000000000 libssl.so.10 SSL_write 0000000000000000 DF *UND* 0000000000000000 OPENSSL_1.0.0 SSL_write
The last two strings in this output are the symbol version and symbol name. Compare these values with the values returned by the following operations to detect symbol version mismatches:
objdump -T <path to SSL libs>/libssl.so.1* objdump -T <path to SSL libs>/libcrypto.so.1*
This procedure is neither exact nor exhaustive: many symbols used by mongod from the libcrypto library do not begin with CRYPTO_.
MongoDB on Windows¶
MongoDB Using MMAPv1¶
Install Hotfix for MongoDB 2.6.6 and Later¶
Microsoft has released a hotfix for Windows 7 and Windows Server 2008 R2, KB2731284, that repairs a bug in these operating systems’ use of memory-mapped files that adversely affects the performance of MongoDB using the MMAPv1 storage engine.
Install this hotfix to obtain significant performance improvements on MongoDB 2.6.6 and later releases in the 2.6 series, which use MMAPv1 exclusively, and on 3.0 and later when using MMAPv1 as the storage engine.
Configure Windows Page File For MMAPv1¶
Configure the page file such that the minimum and maximum page file size are equal and at least 32 GB. Use a multiple of this size if, during peak usage, you expect concurrent writes to many databases or collections. However, the page file size does not need to exceed the maximum size of the database.
A large page file is needed as Windows requires enough space to accommodate all regions of memory mapped files made writable during peak usage, regardless of whether writes actually occur.
The page file is not used for database storage and will not receive writes during normal MongoDB operation. As such, the page file will not affect performance, but it must exist and be large enough to accommodate Windows’ commitment rules during peak database use.
Dynamic page file sizing is too slow to accommodate the rapidly fluctuating commit charge of an active MongoDB deployment. This can result in transient overcommitment situations that may lead to abrupt server shutdown with a VirtualProtect error 1455.
MongoDB 3.0 Using WiredTiger¶
For MongoDB instances using the WiredTiger storage engine, performance on Windows is comparable to performance on Linux.
MongoDB on Virtual Environments¶
This section describes considerations when running MongoDB in some of the more common virtual environments.
For all platforms, consider Scheduling for Virtual Devices.
MongoDB is compatible with EC2.
You may alternately choose to obtain a set of Amazon Machine Images (AMI) that bundle together MongoDB and Amazon’s Provisioned IOPS storage volumes. Provisioned IOPS can greatly increase MongoDB’s performance and ease of use. For more information, see this blog post.
This applies to all Azure deployments, using any guest operating system.
If your volumes have inappropriate cache settings, MongoDB may eventually shut down with the following error:
[DataFileSync] FlushViewOfFile for <data file> failed with error 1 ... [DataFileSync] Fatal Assertion 16387
The performance characteristics of MongoDB may change with READ/WRITE caching enabled.
The TCP keepalive on the Azure load balancer is 240 seconds by default, which can cause it to silently drop connections if the TCP keepalive on your Azure systems is greater than this value. You should set tcp_keepalive_time to 120 to ameliorate this problem.
On Linux systems you can use the following operation to check the value of tcp_keepalive_time:
The value is measured in seconds. You can change the tcp_keepalive_time value with the following operation:
echo <value> > /proc/sys/net/ipv4/tcp_keepalive_time
For Windows systems, issue the following command to view the keep alive setting:
reg query HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters /v KeepAliveTime
The registry value is not present by default. The system default, used if the value is absent, is 7200000 milliseconds or 0x6ddd00 in hexadecimal. To set a shorter keep alive period use the following invocation in an Administrator Command Prompt, where <value> is expressed in hexadecimal (e.g. 0x0124c0 is 120000):
reg add HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ /v KeepAliveTime /d <value>
Windows users should consider the Windows Server Technet Article on KeepAliveTime for more information on setting keep alive for MongoDB deployments on Windows systems.
MongoDB is compatible with VMWare.
As some users have run into issues with VMWare’s memory overcommit feature, you should disable the feature.
Further, MongoDB is known to run poorly with VMWare’s balloon driver (vmmemctl), so you should disable this as well. VMWare uses the balloon driver to reduce physical memory usage on the host hardware by allowing the hypervisor to swap to disk while hiding this fact from the guest, which continues to see the same amount of (virtual) physical memory. This interferes with MongoDB’s memory management, and you are likely to experience significant performance degradation.
It is possible to clone a virtual machine running MongoDB. You might use this function to spin up a new virtual host to add as a member of a replica set. If you clone a VM with journaling enabled, the clone snapshot will be valid. If not using journaling, first stop mongod, then clone the VM, and finally, restart mongod.
On Linux, use the iostat command to check if disk I/O is a bottleneck for your database. Specify a number of seconds when running iostat to avoid displaying stats covering the time since server boot.
For example, the following command will display extended statistics and the time for each displayed report, with traffic in MB/s, at one second intervals:
iostat -xmt 1
Key fields from iostat:
- %util: this is the most useful field for a quick check, it indicates what percent of the time the device/drive is in use.
- avgrq-sz: average request size. Smaller number for this value reflect more random IO operations.