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- mergeChunks
mergeChunks¶
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Definition¶
- mergeChunks¶
For a sharded collection, mergeChunks combines contiguous chunk ranges on a shard into a single chunk. Issue the mergeChunks command from a mongos instance.
mergeChunks has the following form:
db.runCommand( { mergeChunks : <namespace> , bounds : [ { <shardKeyField>: <minFieldValue> }, { <shardKeyField>: <maxFieldValue> } ] } )
For compound shard keys, you must include the full shard key in the bounds specification. If the shard key is { x: 1, y: 1 }, mergeChunks has the following form:
db.runCommand( { mergeChunks : <namespace> , bounds : [ { x: <minValue>, y: <minValue> }, { x: <maxValue>, y: <maxValue> } ] } )
The mergeChunks command has the following fields:
Field Type Description mergeChunks namespace The fully qualified namespace of the collection where both chunks exist. Namespaces take form of <database>.<collection>. bounds array An array that contains the minimum and maximum key values of the new chunk.
Behavior¶
Note
Use the mergeChunks only in special circumstances. For instance, when cleaning up your sharded cluster after removing many documents.
In order to successfully merge chunks, the following must be true:
- In the bounds field, <minkey> and <maxkey> must correspond to the lower and upper bounds of the chunks to merge.
- The chunks must reside on the same shard.
- The chunks must be contiguous.
mergeChunks returns an error if these conditions are not satisfied.
Return Messages¶
On success, mergeChunks returns to following document:
{ "ok" : 1 }
Another Operation in Progress¶
mergeChunks returns the following error message if another metadata operation is in progress on the chunks collection:
errmsg: "The collection's metadata lock is already taken."
If another process, such as balancer process, changes metadata while mergeChunks is running, you may see this error. You can retry the mergeChunks operation without side effects.
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