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MongoDB Server Parameters

Synopsis

MongoDB provides a number of configuration options that are accessible via the setParameter command or --setParameter option.s

For additional run time configuration options, see Configuration File Options and Manual Page for mongod.

Parameters

Authentication Parameters

authenticationMechanisms

Available for MongoDB Enterprise Only

Changed in version 2.6: Added support for the PLAIN and MONGODB-X509 authentication mechanisms.

Available for both mongod and mongos.

Specifies the list of authentication mechanisms the server accepts. Set this to one or more of the following values. If you specify multiple values, use a comma-separated list and no spaces. For descriptions of the authentication mechanisms, see Authentication.

Value	Description
MONGODB-CR	MongoDB challenge/response authentication.
MONGODB-X509	MongoDB TLS/SSL certificate authentication.
PLAIN	External authentication using LDAP. You can also use PLAIN for authenticating in-database users. PLAIN transmits passwords in plain text. This mechanism is available only in MongoDB Enterprise.
GSSAPI	External authentication using Kerberos. This mechanism is available only in MongoDB Enterprise.

For example, to specify PLAIN as the authentication mechanism, use the following command:

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mongod --setParameter authenticationMechanisms=PLAIN --auth

clusterAuthMode

New in version 2.6.

Available for both mongod and mongos.

Set the clusterAuthMode to either sendX509 or x509. Useful during rolling upgrade to use x509 for membership authentication to minimize downtime.

The default distribution of MongoDB does not contain support for TLS/SSL. To use TLS/SSL you can either compile MongoDB with TLS/SSL support or use MongoDB Enterprise. See Configure mongod and mongos for TLS/SSL for more information about TLS/SSL and MongoDB.

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db.getSiblingDB('admin').runCommand( { setParameter: 1, clusterAuthMode: "sendX509" } )

enableLocalhostAuthBypass

New in version 2.4.

Available for both mongod and mongos.

Specify 0 or false to disable localhost authentication bypass. Enabled by default.

enableLocalhostAuthBypass is not available using setParameter database command. Use the setParameter option in the configuration file or the --setParameter option on the command line.

saslauthdPath

Note

Available only in MongoDB Enterprise (except MongoDB Enterprise for Windows).

Specify the path to the Unix Domain Socket of the saslauthd instance to use for proxy authentication.

saslHostName

New in version 2.4.

saslHostName overrides MongoDB’s default hostname detection for the purpose of configuring SASL and Kerberos authentication.

saslHostName does not affect the hostname of the mongod or mongos instance for any purpose beyond the configuration of SASL and Kerberos.

You can only set saslHostName during start-up, and cannot change this setting using the setParameter database command.

Note

saslHostName supports Kerberos authentication and is only included in MongoDB Enterprise. For Linux systems, see Configure MongoDB with Kerberos Authentication on Linux for more information.

saslServiceName

New in version 2.4.6.

Allows users to override the default Kerberos service name component of the Kerberos principal name, on a per-instance basis. If unspecified, the default value is mongodb.

MongoDB only permits setting saslServiceName at startup. The setParameter command can not change this setting.

saslServiceName is only available in MongoDB Enterprise.

Important

Ensure that your driver supports alternate service names.

sslMode

New in version 2.6.

Available for both mongod and mongos.

Set the net.ssl.mode to either preferSSL or requireSSL. Useful during rolling upgrade to TLS/SSL to minimize downtime.

The default distribution of MongoDB does not contain support for TLS/SSL. To use TLS/SSL you can either compile MongoDB with TLS/SSL support or use MongoDB Enterprise. See Configure mongod and mongos for TLS/SSL for more information about TLS/SSL and MongoDB.

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db.getSiblingDB('admin').runCommand( { setParameter: 1, sslMode: "preferSSL" } )

supportCompatibilityFormPrivilegeDocuments

New in version 2.4.

Deprecated since version 2.6: supportCompatibilityFormPrivilegeDocuments has no effect in 2.6 and will be removed in 3.0.

Available for both mongod and mongos.

supportCompatibilityFormPrivilegeDocuments is not available using setParameter database command. Use the setParameter option in the configuration file or the --setParameter option on the command line.

userCacheInvalidationIntervalSecs

New in version 2.6.

Default: 600.

Available for mongos only.

On a mongos instance, this specifies the amount of time in seconds to allow before the mongos instance purges the in-memory cache of user objects. The cache includes the users’ credentials and roles.

This parameter has a minimum value of 30 seconds and a maximum value of 86400 seconds (24 hours).

General Parameters

connPoolMaxShardedConnsPerHost

New in version 2.6.

Default: 200

Available for both mongod and mongos.

Set the maximum size of the connection pools for communication to the shards. The size of a pool does not prevent the creation of additional connections, but does prevent the connection pools from retaining connections above this limit.

Increase the connPoolMaxShardedConnsPerHost value only if the number of connections in a connection pool has a high level of churn or if the total number of created connections increase.

You can only set connPoolMaxShardedConnsPerHost during startup in the config file or on the command line, as follows to increase the size of the connection pool:

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mongos --setParameter connPoolMaxShardedConnsPerHost=250

connPoolMaxConnsPerHost

New in version 2.6.

Default: 200

Available for both mongod and mongos.

Set the maximum size of the connection pools for outgoing connections to other mongod instances. The size of a pool does not prevent the creation of additional connections, but does prevent a connection pool from retaining connections in excess of the value of connPoolMaxConnsPerHost.

Only adjust this setting if your driver does not pool connections and you’re using authentication in the context of a sharded cluster.

You can only set connPoolMaxConnsPerHost during startup in the config file or on the command line, as in the following example:

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mongod --setParameter connPoolMaxConnsPerHost=250

cursorTimeoutMillis

New in version 2.6.9.

Default: 600000 (i.e. 10 minutes)

Available for both mongod and mongos.

Sets the expiration threshold in milliseconds for idle cursors before MongoDB removes them; i.e. MongoDB removes cursors that have been idle for the specified cursorTimeoutMillis.

For example, the following sets the cursorTimeoutMillis to 300000 milliseconds (i.e. 5 minutes).

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mongod --setParameter cursorTimeoutMillis=300000

Or, if using the setParameter command within the mongo shell:

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db.getSiblingDB('admin').runCommand( { setParameter: 1, cursorTimeoutMillis: 300000 } )

failIndexKeyTooLong

New in version 2.6.

Available for mongod only.

In MongoDB 2.6, if you attempt to insert or update a document so that the value of an indexed field is longer than the Index Key Length Limit, the operation will fail and return an error to the client. In previous versions of MongoDB, these operations would successfully insert or modify a document but the index or indexes would not include references to the document.

To avoid this issue, consider using hashed indexes or indexing a computed value. If you have an existing data set and want to disable this behavior so you can upgrade and then gradually resolve these indexing issues, you can use failIndexKeyTooLong to disable this behavior.

failIndexKeyTooLong defaults to true. When false, a 2.6 mongod instance will provide the 2.4 behavior.

Issue the following command to disable the index key length validation: for a running:binary:~bin.mongod instance:

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db.getSiblingDB('admin').runCommand( { setParameter: 1, failIndexKeyTooLong: false } )

You can also set failIndexKeyTooLong at run-time with the following operation.

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mongod --setParameter failIndexKeyTooLong=false

notablescan

Available for mongod only.

Specify whether all queries must use indexes. If 1, MongoDB will not execute queries that require a collection scan and will return an error.

Consider the following example which sets notablescan to 1 or true:

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db.getSiblingDB("admin").runCommand( { setParameter: 1, notablescan: 1 } )

Setting notablescan to 1 can be useful for testing application queries, for example, to identify queries that scan an entire collection and cannot use an index.

To detect unindexed queries without notablescan, consider reading the Evaluate Performance of Current Operations and Optimize Query Performance sections and using the logLevel parameter, mongostat and profiling.

Don’t run production mongod instances with notablescan because preventing collection scans can potentially affect queries in all databases, including administrative queries.

newCollectionsUsePowerOf2Sizes

New in version 2.6.

Default: true.

Available for mongod only.

mongod uses an allocation strategy called usePowerOf2Sizes where each record has a size, in bytes that is a power of 2 (e.g. 32, 64, 128, 256, 512…16777216.) The minimum allocation for a document is 32 bytes.

MongoDB stores documents in contiguous spaces on disk, and each record includes both the document itself and some additional space to allow the document to grow slightly through updates.

By default, all new collections, created after 2.6 use the usePowerOf2Sizes strategy. To revert to the prior exact fit allocation strategy, set newCollectionsUsePowerOf2Sizes to false.

New collections include those: created during initial sync, as well as those created by the mongorestore and mongoimport tools, by running mongod with the --repair option, as well as the restoreDatabase command.

Issue the following command to change the allocation strategy for a running mongod instance:

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db.getSiblingDB('admin').runCommand( { setParameter: 1, newCollectionsUsePowerOf2Sizes: false } )

You can also set newCollectionsUsePowerOf2Sizes at run-time with the following operation.

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mongod --setParameter newCollectionsUsePowerOf2Sizes=false

releaseConnectionsAfterResponse

New in version 2.2.4: and 2.4.2

Available for both mongod and mongos.

Changes the behavior of the connection pool that mongos uses to connect to the shards. As a result, each mongos should need to maintain fewer connections to each shard. When enabled, the mongos will release a connection into the thread pool after each read operation or command.

Warning

For applications that do not use the default, journaled, or replica acknowledged write concern modes of the driver, releaseConnectionsAfterResponse will affect the meaning of getLastError.

If an application allows read operations in between write operations and getLastError calls, the resulting getLastError will not report on the success of the proceeding write operation.

Use with caution.

To enable, use the following command while connected to a mongos:

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db.getSiblingDB('admin').runCommand( { setParameter: 1, releaseConnectionsAfterResponse: true } )

Alternately, you may start the mongos instance with the following run-time option:

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mongos --setParameter releaseConnectionsAfterResponse=true

To change this policy for the entire cluster, you must set releaseConnectionsAfterResponse on each mongos instance in the cluster.

textSearchEnabled

Deprecated since version 2.6: MongoDB enables the text search feature by default. Manual enabling of this feature is unnecessary.

Available for both mongod and mongos.

Enables the text search feature. When manually enabling, you must enable on each and every mongod for replica sets.

ttlMonitorEnabled

New in version 2.4.6.

Available for mongod only.

To support TTL Indexes, mongod instances have a background thread that is responsible for deleting documents from collections with TTL indexes.

To disable this worker thread for a mongod, set ttlMonitorEnabled to false, as in the following operations:

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db.getSiblingDB('admin').runCommand( { setParameter: 1, ttlMonitorEnabled: false } )

Alternately, you may disable the thread at run-time by starting the mongod instance with the following option:

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mongod --setParameter ttlMonitorEnabled=false

Logging Parameters

logLevel

Available for both mongod and mongos.

Specify an integer between 0 and 5 signifying the verbosity of the logging, where 5 is the most verbose.

Consider the following example which sets the logLevel to 2:

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use admin
db.runCommand( { setParameter: 1, logLevel: 2 } )

The default logLevel is 0.

See also

verbosity.

logUserIds

New in version 2.4.

Available for both mongod and mongos.

Specify 1 to enable logging of userids.

Disabled by default.

quiet

Available for both mongod and mongos.

Sets quiet logging mode. If 1, mongod will go into a quiet logging mode which will not log the following events/activities:

• connection events;
• the drop command, the dropIndexes command, the diagLogging command, the validate command, and the clean command; and
• replication synchronization activities.

Consider the following example which sets the quiet to 1:

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db = db.getSiblingDB("admin")
db.runCommand( { setParameter: 1, quiet: 1 } )

See also

quiet

traceExceptions

New in version 2.2.

Configures mongod to log full source code stack traces for every database and socket C++ exception, for use with debugging. If true, mongod will log full stack traces.

Consider the following example which sets the traceExceptions to true:

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db.getSiblingDB("admin").runCommand( { setParameter: 1, traceExceptions: true } )

See also

systemLog.traceAllExceptions

Replication Parameters

replApplyBatchSize

Available for mongod only.

Specify the number of oplog entries to apply as a single batch. replApplyBatchSize must be an integer between 1 and 1024. The default value is 1. This option only applies to master/slave configurations and is valid only on a mongod started with the --slave command line option.

Batch sizes must be 1 for members with slavedelay configured.

replIndexPrefetch

New in version 2.2.

Available for mongod only.

Use replIndexPrefetch in conjunction with replSetName when configuring a replica set. The default value is all and available options are:

• none
• all
• _id_only

By default secondary members of a replica set will load all indexes related to an operation into memory before applying operations from the oplog. You can modify this behavior so that the secondaries will only load the _id index. Specify _id_only or none to prevent the mongod from loading any index into memory.

Storage Parameters

journalCommitInterval

Specify an integer between 1 and 500 signifying the number of milliseconds (ms) between journal commits.

Consider the following example which sets the journalCommitInterval to 200 ms:

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db.getSiblingDB("admin").runCommand( { setParameter: 1, journalCommitInterval: 200 } )

See also

commitIntervalMs.

syncdelay

Available for mongod only.

Specify the interval in seconds between fsync operations where mongod flushes its working memory to disk. By default, mongod flushes memory to disk every 60 seconds. In almost every situation you should not set this value and use the default setting.

Consider the following example which sets the syncdelay to 60 seconds:

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db.getSiblingDB("admin").runCommand( { setParameter: 1, syncdelay: 60 } )

See also

syncPeriodSecs and journalCommitInterval.

Auditing Parameters

auditAuthorizationSuccess

Note

Available only in MongoDB Enterprise.

New in version 2.6.5.

Default: false

Enables the auditing of authorization successes for the authCheck action.

When auditAuthorizationSuccess is false, the audit system only logs the authorization failures for authCheck.

To enable the audit of authorization successes, issue the following command:

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db.adminCommand( { setParameter: 1, auditAuthorizationSuccess: true } )

Enabling auditAuthorizationSuccess degrades performance more than logging only the authorization failures.

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