isMaster¶

Client Disconnection¶

Starting in MongoDB 4.2, if the client that issued the isMaster disconnects before the operation completes, MongoDB marks the isMaster for termination (i.e. killOp on the operation).

All Instances¶

The following isMaster fields are common across all roles:

isMaster.ismaster¶

A boolean value that reports when this node is writable. If true, then this instance is a primary in a replica set, or a mongos instance, or a standalone mongod.

This field will be false if the instance is a secondary member of a replica set or if the member is an arbiter of a replica set.

isMaster.topologyVersion¶

For internal use by MongoDB.

New in version 4.4.版本4.4中的新功能。

isMaster.maxBsonObjectSize¶

The maximum permitted size of a BSON object in bytes for this mongod process. If not provided, clients should assume a max size of “16 * 1024 * 1024”.

isMaster.maxMessageSizeBytes¶

The maximum permitted size of a BSON wire protocol message. The default value is 48000000 bytes.

isMaster.maxWriteBatchSize¶

The maximum number of write operations permitted in a write batch. If a batch exceeds this limit, the client driver divides the batch into smaller groups each with counts less than or equal to the value of this field.

The value of this limit is 100,000 writes.

Changed in version 3.6.在版本3.6中更改。The limit raises from 1,000 to 100,000 writes. This limit also applies to legacy OP_INSERT messages.

isMaster.localTime¶

Returns the local server time in UTC. This value is an ISO date.

isMaster.logicalSessionTimeoutMinutes¶

New in version 3.6.版本3.6中的新功能。

The time in minutes that a session remains active after its most recent use. Sessions that have not received a new read/write operation from the client or been refreshed with refreshSessions within this threshold are cleared from the cache. State associated with an expired session may be cleaned up by the server at any time.

Only available when featureCompatibilityVersion is "3.6" or greater. See Backwards Incompatible Features.

isMaster.connectionId¶

New in version 4.2.版本4.2中的新功能。

An identifier for the mongod/mongos instance’s outgoing connection to the client.

isMaster.minWireVersion¶

The earliest version of the wire protocol that this mongod or mongos instance is capable of using to communicate with clients.

Clients may use minWireVersion to help negotiate compatibility with MongoDB.

isMaster.maxWireVersion¶

The latest version of the wire protocol that this mongod or mongos instance is capable of using to communicate with clients.

Clients may use maxWireVersion to help negotiate compatibility with MongoDB.

isMaster.readOnly¶

New in version 3.4.版本3.4中的新功能。

A boolean value that, when true, indicates that the mongod or mongos is running in read-only mode.

isMaster.compression¶

New in version 3.4.版本3.4中的新功能。

An array listing the compression algorithms used or available for use (i.e. common to both the client and the mongod or mongos instance) to compress the communication between the client and the mongod or mongos instance.

The field is only available if compression is used. For example:例如：

• If the mongod is enabled to use both the snappy,zlib compressors and a client has specified zlib, the compression field would contain:

  "compression": [ "zlib" ]

• If the mongod is enabled to use both the snappy,zlib compressors and a client has specified zlib,snappy, the compression field would contain:

  "compression": [ "zlib", "snappy" ]

• If the mongod is enabled to use the snappy compressor and a client has specified zlib,snappy, the compression field would contain :

  "compression": [ "snappy" ]

• If the mongod is enabled to use the snappy compressor and a client has specified zlib or the client has specified no compressor, the field is omitted.

That is, if the client does not specify compression or if the client specifies a compressor not enabled for the connected mongod or mongos instance, the field does not return.

isMaster.saslSupportedMechs¶

An array of SASL mechanisms used to create the user’s credential or credentials. Supported SASL mechanisms are:

• GSSAPI
• SCRAM-SHA-256
• SCRAM-SHA-1

The field is returned only when the command is run with the saslSupportedMechs field:

db.runCommand( { isMaster: 1, saslSupportedMechs: "<db.username>" } )

Sharded Instances¶

mongos instances add the following field to the isMaster response document:

isMaster.msg¶

Contains the value isdbgrid when isMaster returns from a mongos instance.

Replica Sets¶

isMaster contains these fields when returned by a member of a replica set:

isMaster.hosts¶

An array of strings in the format of "[hostname]:[port]" that lists all members of the replica set that are neither hidden, passive, nor arbiters.

Drivers use this array and the isMaster.passives to determine which members to read from.

isMaster.setName¶

The name of the current :replica set.

isMaster.setVersion¶

The current replica set config version.

isMaster.secondary¶

A boolean value that, when true, indicates if the mongod is a secondary member of a replica set.

isMaster.passives¶

An array of strings in the format of "[hostname]:[port]" listing all members of the replica set which have a members[n].priority of 0.

This field only appears if there is at least one member with a members[n].priority of 0.

Drivers use this array and the isMaster.hosts to determine which members to read from.

isMaster.arbiters¶

An array of strings in the format of "[hostname]:[port]" listing all members of the replica set that are arbiters.

This field only appears if there is at least one arbiter in the replica set.

isMaster.primary¶

A string in the format of "[hostname]:[port]" listing the current primary member of the replica set.

isMaster.arbiterOnly¶

A boolean value that , when true, indicates that the current instance is an arbiter. The arbiterOnly field is only present, if the instance is an arbiter.

isMaster.passive¶

A boolean value that, when true, indicates that the current instance is passive. The passive field is only present for members with a members[n].priority of 0.

isMaster.hidden¶

A boolean value that, when true, indicates that the current instance is hidden. The hidden field is only present for hidden members.

isMaster.tags¶

A tags document contains user-defined tag field and value pairs for the replica set member.

{ "<tag1>": "<string1>", "<tag2>": "<string2>",... }

• For read operations, you can specify a tag set in the read preference to direct the operations to replica set member(s) with the specified tag(s).
• For write operations, you can create a customize write concern using settings.getLastErrorModes and settings.getLastErrorDefaults.

For more information, see Configure Replica Set Tag Sets.

See also参阅

members[n].tags

isMaster.me¶

The [hostname]:[port] of the member that returned isMaster.

isMaster.electionId¶

A unique identifier for each election. Included only in the output of isMaster for the primary. Used by clients to determine when elections occur.

isMaster.lastWrite¶

New in version 3.4.版本3.4中的新功能。

A document containing optime and date information for the database’s most recent write operation.

isMaster.lastWrite.opTime¶

An object giving the optime of the last write operation.

isMaster.lastWrite.lastWriteDate¶

A date object containing the time of the last write operation.

isMaster.lastWrite.majorityOpTime¶

An object giving the optime of the last write operation readable by majority reads.

isMaster.lastWrite.majorityWriteDate¶

A date object containing the time of the last write operation readable by majority reads.

For details on the ok status field, the operationTime field, and the $clusterTime field, see Command Response.