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Database Manual

Change Streams

Change Events

reshardCollection Event

Summary

reshardCollection

New in version 6.1: (Also available in 6.0.14)

A reshardCollection event occurs when:

The shard key for a collection and the distribution of your data is changed, and
The change stream has showExpandedEvents set to true.

Description

Field

Type

Description

_id

Document

A BSON object which serves as an identifier for the change stream event. This value is used as the resumeToken for the resumeAfter parameter when resuming a change stream. The _id object has the following form:

{
   "_data" : <BinData|hex string>
}

The _data type depends on the MongoDB versions and, in some cases, the feature compatibility version (FCV) at the time of the change stream's opening or resumption. See Resume Tokens for the full list of _data types.

For an example of resuming a change stream by resumeToken, see Resume a Change Stream.

clusterTime

Timestamp

clusterTime is the timestamp from the oplog entry associated with the event.

Due to oplog size limits, multi-document transactions may create multiple oplog entries. In a transaction, change stream events staged in a given oplog entry share the same clusterTime.

On sharded clusters, events with the same clusterTime may not all relate to the same transaction. Some events don't relate to a transaction at all.

To identify events for a single transaction, you can use the combination of lsid and txnNumber in the change stream event document.

collectionUUID

UUID

UUID identifying the collection where the change occurred.

New in version 6.0.

ns

Document

The namespace (database and or collection) affected by the event.

ns.coll

String

The name of the collection where the event occurred.

ns.db

String

The name of the database where the event occurred.

operationDescription

Document

Additional information on the change operation.

This document and its subfields only appears when the change stream uses expanded events.

New in version 6.0.

operationDescription.

reshardUUID

UUID

UUID that identifies the resharding operation.

New in version 6.1.

operationDescription. | shardKey

Document

The shard key for the collection where the change occurred.

New in version 6.0.

operationDescription. | oldShardKey

Document

The shard key for the collection that changed.

New in version 6.1.

operationDescription. | unique

Boolean

This has a value of true if the collection was sharded with a unique shard key.

New in version 6.0.

operationDescription. | numInitialChunks

NumberLong

Number of chunks created on each shard during a shardCollection operation.

New in version 6.0.

operationDescription.

collation

Document

Collation document used for the shard key index.

New in version 6.1.

operationDescription.

zones

Array

The zones added for the new shard key.

New in version 6.1.

Example

The following example shows a reshardCollection event:

{
   "_id": { <ResumeToken> },
   "operationType": "reshardCollection",
   "collectionUUID": 0,
   "ns": {"db": "reshard_collection_event", "coll": "coll"},
   "operationDescription": {
     "reshardUUID": 0,
     "shardKey": {"newKey": 1},
     "oldShardKey": {"_id": 1},
     "unique": false,
     "numInitialChunks": NumberLong(1),
     "collation": {"locale": "simple"},
     "zones": [
         {"zone": "zone1", "min": {"newKey": {"$minKey": 1}}, "max": {"newKey": {"$maxKey": 1}}}
     ]
   }
}

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