mergeChunks (database command数据库命令)

Definition定义

mergeChunks

For a sharded collection, mergeChunks combines contiguous chunk ranges on a shard into a single chunk. Issue the mergeChunks command on the admin database from a mongos instance.对于分片集合，mergeChunks将分片上的连续块范围组合成一个块。从mongos实例对管理数据库发出mergeChunks命令。

Compatibility兼容性

This command is available in deployments hosted in the following environments:此命令在以下环境中托管的部署中可用：

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud：云中MongoDB部署的完全托管服务

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB：MongoDB的基于订阅的自我管理版本
• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB：MongoDB的源代码可用、免费使用和自我管理版本

Syntax语法

The command has the following syntax:该命令具有以下语法：

db.adminCommand(
   {
     mergeChunks: <namespace>,
     bounds : [
       { <shardKeyField>: <minFieldValue> },
       { <shardKeyField>: <maxFieldValue> }
     ]
   }
)

For compound shard keys, you must include the full shard key in the bounds specification. For example, if the shard key is { x: 1, y: 1 }, mergeChunks has the following form:对于复合分片键，您必须在bounds规范中包含完整的分片键。例如，如果分片键是{ x: 1, y: 1 }，那么mergeChunks的形式如下：

db.adminCommand(
   {
     mergeChunks: <namespace>,
     bounds: [
       { x: <minValue>, y: <minValue> },
       { x: <maxValue>, y: <maxValue> }
     ]
   }
 )

Command Fields命令字段

The command takes the following fields:该命令包含以下字段：

Access Control访问控制

On deployments running with authorization, the built-in role clusterManager provides the required privileges.在authorization运行的部署中，内置的角色clusterManager提供所需的权限。

Behavior行为

In order to successfully merge chunks, the following must be true:为了成功合并块，必须满足以下条件：

• In the bounds field, <minkey> and <maxkey> must correspond to the lower and upper bounds of the chunks to merge.在边界字段中，<minkey>和<maxkey>必须对应于要合并的块的下限和上限。
• The chunks must reside on the same shard.这些块必须位于同一个分片上。
• The chunks must be contiguous.这些块必须是连续的。

mergeChunks returns an error if these conditions are not satisfied.如果不满足这些条件，则返回错误。

Return Messages返回消息

On success, mergeChunks returns this document:成功后，mergeChunks将返回以下文档：

{
  "ok" : 1,
  "$clusterTime" : {
     "clusterTime" : Timestamp(1510767081, 1),
     "signature" : {
         "hash" : BinData(0,"okKHD0QuzcpbVQg7mP2YFw6lM04="),
         "keyId" : Long("6488693018630029321")
      }
  },
  "operationTime" : Timestamp(1510767081, 1)
}

errmsg: "The collection's metadata lock is already taken."

{
  "ok" : 0,
  "errmsg" : "could not merge chunks, collection test.users does not contain a chunk ending at { username: \"user63169\" }",
  "$clusterTime" : {
     "clusterTime" : Timestamp(1510767081, 1),
     "signature" : {
         "hash" : BinData(0,"okKHD0QuzcpbVQg7mP2YFw6lM04="),
         "keyId" : Long("6488693018630029321")
      }
  },
  "operationTime" : Timestamp(1510767081, 1)
}

{
  "ok" : 0,
  "errmsg" : "could not merge chunks, collection test.users has more than 2 chunks between [{ username: \"user29937\" }, { username: \"user49877\" })"
  "$clusterTime" : {
     "clusterTime" : Timestamp(1510767081, 1),
     "signature" : {
         "hash" : BinData(0,"okKHD0QuzcpbVQg7mP2YFw6lM04="),
         "keyId" : Long("6488693018630029321")
      }
  },
  "operationTime" : Timestamp(1510767081, 1)

}