mergeAllChunksOnShard (database command数据库命令)

Definition定义

mergeAllChunksOnShard

mergeAllChunksOnShard finds and merges all mergeable chunks that a shard owns for a given collection.查找并合并一个分片为给定集合拥有的所有可合并块。

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(
  {
    mergeAllChunksOnShard: <name of the collection>,
    shard: <name of the shard>,
    maxNumberOfChunksToMerge: <maximum number of chunks to merge> /* optional */
  }
)

Command Fields命令字段

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

Behavior行为

mergeAllChunksOnShard finds and merges all mergeable chunks for a collection on the same shard. Two or more contiguous chunks in the same collection are mergeable when they meet all of these conditions:查找并合并同一分片上集合的所有可合并块。当同一集合中的两个或多个连续块满足所有这些条件时，它们是可以合并的：

• They are owned by the same shard.它们属于同一个分片。
• They are not jumbo chunks. jumbo chunks are not mergeable because they cannot participate in migrations.它们不是jumbo块的。jumbo块不可合并，因为它们不能参与迁移。

• Their history can be purged safely, without breaking transactions and snapshot reads:可以安全地清除它们的历史记录，而不会中断事务和快照读取：

  • The last migration involving the chunk happened at least as many seconds ago as the value of minSnapshotHistoryWindowInSeconds.最后一次涉及块的迁移发生在至少与minSnapshotHistoryWindowInSeconds的值一样多的秒前。
  • The last migration involving the chunk happened at least as many seconds ago as the value of transactionLifetimeLimitSeconds.涉及块的最后一次迁移发生在至少与transactionLifetimeLimitSeconds的值一样多的秒前。

Example示例

This example assumes that history is empty for all chunks and all chunks are non-jumbo. Since both conditions are true, all contiguous intervals on the same shard are mergeable.此示例假设所有块的历史记录都是空的，并且所有块都是非巨型的。由于这两个条件都为真，因此同一分片上的所有连续区间都是可合并的。

db.adminCommand( { mergeAllChunksOnShard: "db.coll", shard: "Shard0" } )

db.adminCommand( { mergeAllChunksOnShard: "db.coll", shard: "Shard1" } )