getLastError¶

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Definition¶

getLastError¶

Changed in version 2.6: A new protocol for write operations integrates write concerns with the write operations, eliminating the need for a separate getLastError. Most write methods now return the status of the write operation, including error information. In previous versions, clients typically used the getLastError in combination with a write operation to verify that the write succeeded.

Returns the error status of the preceding write operation on the current connection.

getLastError uses the following prototype form:

{ getLastError: 1 }

getLastError uses the following fields:

Field Type Description

j boolean If true, wait for the next journal commit before returning, rather than waiting for a full disk flush. If mongod does not have journaling enabled, this option has no effect. If this option is enabled for a write operation, mongod will wait no more than 1/3 of the current commitIntervalMs before writing data to the journal.

w

integer or string

When running with replication, this is the number of servers to replicate to before returning. A w value of 1 indicates the primary only. A w value of 2 includes the primary and at least one secondary, etc. In place of a number, you may also set w to majority to indicate that the command should wait until the latest write propagates to a majority of the voting replica set members.

Changed in version 3.0: In previous versions, majority referred to the majority of all members of the replica set instead of the majority of the voting members.

If using w, you should also use wtimeout. Specifying a value for w without also providing a wtimeout may cause getLastError to block indefinitely.

wtimeout integer Optional. Milliseconds. Specify a value in milliseconds to control how long to wait for write propagation to complete. If replication does not complete in the given timeframe, the getLastError command will return with an error status.

Output¶

Each getLastError() command returns a document containing a subset of the fields listed below.

getLastError.ok¶: ok is true when the getLastError command completes successfully.

Note

A value of true does not indicate that the preceding operation did not produce an error.

getLastError.err¶: err is null unless an error occurs. When there was an error with the preceding operation, err contains a string identifying the error.

getLastError.errmsg¶: New in version 2.6.

errmsg contains the description of the error. errmsg only appears if there was an error with the preceding operation.

getLastError.code¶: code reports the preceding operation’s error code. For description of the error, see err and errmsg.

getLastError.connectionId¶: The identifier of the connection.

getLastError.lastOp¶: When issued against a replica set member and the preceding operation was a write or update, lastOp is the optime timestamp in the oplog of the change.

getLastError.n¶

If the preceding operation was an update or a remove operation, but not a findAndModify operation, n reports the number of documents matched by the update or remove operation.

For a remove operation, the number of matched documents will equal the number removed.

For an update operation, if the operation results in no change to the document, such as setting the value of the field to its current value, the number of matched documents may be smaller than the number of documents actually modified. If the update includes the upsert:true option and results in the creation of a new document, n returns the number of documents inserted.

n is 0 if reporting on an update or remove that occurs through a findAndModify operation.

getLastError.syncMillis¶: syncMillis is the number of milliseconds spent waiting for the write to disk operation (e.g. write to journal files).

getLastError.shards¶: When issued against a sharded cluster after a write operation, shards identifies the shards targeted in the write operation. shards is present in the output only if the write operation targets multiple shards.

getLastError.singleShard¶: When issued against a sharded cluster after a write operation, identifies the shard targeted in the write operation. singleShard is only present if the write operation targets exactly one shard.

getLastError.updatedExisting¶: updatedExisting is true when an update affects at least one document and does not result in an upsert.

getLastError.upserted¶: If the update results in an insert, upserted is the value of _id field of the document.

Changed in version 2.6: Earlier versions of MongoDB included upserted only if _id was an ObjectId.

getLastError.wnote¶: If set, wnote indicates that the preceding operation’s error relates to using the w parameter to getLastError.

See

Write Concern for more information about w values.

getLastError.wtimeout¶: wtimeout is true if the getLastError timed out because of the wtimeout setting to getLastError.

getLastError.waited¶: If the preceding operation specified a timeout using the wtimeout setting to getLastError, then waited reports the number of milliseconds getLastError waited before timing out.

getLastError.wtime¶: getLastError.wtime is the number of milliseconds spent waiting for the preceding operation to complete. If getLastError timed out, wtime and getLastError.waited are equal.

getLastError.writtenTo¶: If writing to a replica set, writtenTo is an array that contains the hostname and port number of the members that confirmed the previous write operation, based on the value of the w field in the command.

Examples¶

Confirm Replication to Two Replica Set Members¶

The following example ensures the preceding operation has replicated to two members (the primary and one other member). The command also specifies a timeout of 5000 milliseconds to ensure that the:dbcommand:getLastError command does not block forever if MongoDB cannot satisfy the requested write concern:

db.runCommand( { getLastError: 1, w: 2, wtimeout:5000 } )

Confirm Replication to a Majority of a Replica Set¶

The following example ensures the write operation has replicated to a majority of the voting members of the replica set. The command also specifies a timeout of 5000 milliseconds to ensure that the:dbcommand:getLastError command does not block forever if MongoDB cannot satisfy the requested write concern:

db.runCommand( { getLastError: 1, w: "majority", wtimeout:5000 } )

Changed in version 2.6: In Master/Slave deployments, MongoDB treats w: "majority" as equivalent to w: 1. In earlier versions of MongoDB, w: "majority" produces an error in master/slave deployments.

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