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The following checklist, along with the Development Checklist list, provides recommendations to help you avoid issues in your production MongoDB deployment.
- Align your disk partitions with your RAID configuration.
- Avoid using NFS drives for your
dbPath. Using NFS drives can result in degraded and unstable performance. See: Remote Filesystems for more information.
- VMWare users should use VMWare virtual drives over NFS.
- Linux/Unix: format your drives into XFS or EXT4. If possible, use
XFS as it generally performs better with MongoDB.
- With the WiredTiger storage engine, use of XFS is strongly recommended to avoid performance issues found when using EXT4 with WiredTiger.
- If using RAID, you may need to configure XFS with your RAID geometry.
- Windows: use the NTFS file system. Do not use any FAT file system (i.e. FAT 16/32/exFAT).
Verify that all non-hidden replica set members are identically provisioned in terms of their RAM, CPU, disk, network setup, etc.
Configure the oplog size to suit your use case:
The replication oplog window should cover normal maintenance and downtime windows to avoid the need for a full resync.
The replication oplog window should cover the time needed to restore a replica set member from the last backup.
Changed in version 3.4: The replication oplog window no longer needs to cover the time needed to restore a replica set member via initial sync as the oplog records are pulled during the data copy. However, the member being restored must have enough disk space in the local database to temporarily store these oplog records for the duration of this data copy stage.
With earlier versions of MongoDB, replication oplog window should cover the time needed to restore a replica set member by initial sync.
Ensure that your replica set includes at least three data-bearing nodes that run with journaling and that you issue writes with
w:"majority"write concern for availability and durability.
Use hostnames when configuring replica set members, rather than IP addresses.
Ensure full bidirectional network connectivity between all
Ensure that each host can resolve itself.
Ensure that your replica set contains an odd number of voting members.
For high availability, deploy your replica set into a minimum of three data centers.
Journaling: MMAPv1 Storage Engine¶
- Ensure that all instances use journaling.
- Place the journal on its own low-latency disk for write-intensive workloads. Note that this will affect snapshot-style backups as the files constituting the state of the database will reside on separate volumes.
- Use RAID10 and SSD drives for optimal performance.
- SAN and Virtualization:
Deployments to Cloud Hardware¶
- Windows Azure: Adjust the TCP keepalive (
tcp_keepalive_time) to 100-120. The default TTL for TCP connections on Windows Azure load balancers is too slow for MongoDB’s connection pooling behavior.
- Use MongoDB version 2.6.4 or later on systems with high-latency storage, such as Windows Azure, as these versions include performance improvements for those systems. See: Azure Deployment Recommendations for more information.
Operating System Configuration¶
Turn off transparent hugepages and defrag. See Transparent Huge Pages Settings for more information.
Adjust the readahead settings on the devices storing your database files to suit your use case.
- For the MMAPv1 storage engine, if your working set is bigger that the available RAM, and the document access pattern is random, consider lowering the readahead to 32 or 16. Evaluate different settings to find an optimal value that maximizes the resident memory and lowers the number of page faults.
- For the WiredTiger storage engine, set readahead to 0 regardless of storage media type (spinning, SSD, etc.). In general, use the recommended readahead setting unless testing shows a measurable, repeatable, and reliable benefit in a higher readahead value. MongoDB Professional Support can provide advice and guidance on non-zero readahead configurations.
tunedtool if you are running RHEL 7 / CentOS 7 in a virtual environment.
When RHEL 7 / CentOS 7 run in a virtual environment, the
tunedtool automatically invokes a performance profile derived from performance throughput, which automatically sets the readahead settings to 4MB. This can negatively impact performance.
deadlinedisk schedulers for SSD drives.
noopdisk scheduler for virtualized drives in guest VMs.
ulimitvalues on your hardware to suit your use case. If multiple
mongosinstances are running under the same user, scale the
ulimitvalues accordingly. See: UNIX ulimit Settings for more information.
Configure sufficient file handles (
fs.file-max), kernel pid limit (
kernel.pid_max), and maximum threads per process (
kernel.threads-max) for your deployment. For large systems, the following values provide a good starting point:
fs.file-maxvalue of 98000,
kernel.pid_maxvalue of 64000, and
kernel.threads-maxvalue of 64000
Ensure that your system has swap space configured. Refer to your operating system’s documentation for details on appropriate sizing.
Ensure that the system default TCP keepalive is set correctly. A value of 300 often provides better performance for replica sets and sharded clusters. See: Does TCP keepalive time affect MongoDB Deployments? in the Frequently Asked Questions for more information.
- Consider disabling NTFS “last access time” updates. This is
analogous to disabling
atimeon Unix-like systems.
- Schedule periodic tests of your back up and restore process to have time estimates on hand, and to verify its functionality.
Use MongoDB Cloud Manager or Ops Manager, an on-premise solution available in MongoDB Enterprise Advanced or another monitoring system to monitor key database metrics and set up alerts for them. Include alerts for the following metrics:
- lock percent (for the MMAPv1 storage engine)
- replication lag
- replication oplog window
- page faults
Monitor hardware statistics for your servers. In particular, pay attention to the disk use, CPU, and available disk space.
In the absence of disk space monitoring, or as a precaution:
- Create a dummy 4 GB file on the
storage.dbPathdrive to ensure available space if the disk becomes full.
- A combination of
cron+dfcan alert when disk space hits a high-water mark, if no other monitoring tool is available.
- Create a dummy 4 GB file on the
- Configure load balancers to enable “sticky sessions” or “client affinity”, with a sufficient timeout for existing connections.
- Avoid placing load balancers between MongoDB cluster or replica set components.