Rolling Index Builds on Sharded Clusters滚动索引建立在分片集群上¶

Considerations考虑事项¶

Prerequisites先决条件¶

For building unique indexes用于构建唯一索引

1. To create unique indexes using the following procedure, you must stop all writes to the collection during the index build. 要使用以下过程创建唯一索引，必须在索引生成期间停止对集合的所有写入。Otherwise, you may end up with inconsistent data across the replica set members. 否则，可能会导致副本集成员之间的数据不一致。If you cannot stop all writes to the collection, do not use the following procedure to create unique indexes.如果无法停止对集合的所有写入，请不要使用以下过程创建唯一索引。

   Warning

   If you cannot stop all writes to the collection, do not use the following procedure to create unique indexes.如果无法停止对集合的所有写入，请不要使用以下过程创建唯一索引。

2. Before creating the index, validate that no documents in the collection violate the index constraints. 在创建索引之前，请确认集合中没有文档违反索引约束。If a collection is distributed across shards and a shard contains a chunk with duplicate documents, the create index operation may succeed on the shards without duplicates but not on the shard with duplicates. 如果一个集合分布在多个碎片上，并且一个碎片包含一个包含重复文档的区块，那么创建索引操作可能会在没有重复文档的碎片上成功，但在有重复文档的碎片上不会成功。To avoid leaving inconsistent indexes across shards, you can issue the db.collection.dropIndex() from a mongos to drop the index from the collection.为了避免在碎片之间留下不一致的索引，可以从mongos发出db.collection.dropIndex()命令，从集合中删除索引。

Procedure程序¶

sh.stopBalancer()

sh.getBalancerState()

db.adminCommand( { flushRouterConfig: "test.records" } );
db.records.getShardDistribution();

Shard shardA at shardA/s1-mongo1.example.net:27018,s1-mongo2.example.net:27018,s1-mongo3.example.net:27018
 data : 1KiB docs : 50 chunks : 1
 estimated data per chunk : 1KiB
 estimated docs per chunk : 50

Shard shardC at shardC/s3-mongo1.example.net:27018,s3-mongo2.example.net:27018,s3-mongo3.example.net:27018
 data : 1KiB docs : 50 chunks : 1
 estimated data per chunk : 1KiB
 estimated docs per chunk : 50

Totals
 data : 3KiB docs : 100 chunks : 2
 Shard shardA contains 50% data, 50% docs in cluster, avg obj size on shard : 40B
 Shard shardC contains 50% data, 50% docs in cluster, avg obj size on shard : 40B

net:
   bindIp: localhost,<hostname(s)|ip address(es)>
   port: 27218
#   port: 27018
#replication:
#   replSetName: shardA
#sharding:
#   clusterRole: shardsvr
setParameter:
   skipShardingConfigurationChecks: true
   disableLogicalSessionCacheRefresh: true

mongod --config <path/To/ConfigFile>

mongod --port 27218 --setParameter skipShardingConfigurationChecks=true --setParameter disableLogicalSessionCacheRefresh=true

db.records.createIndex( { username: 1 } )

net:
   bindIp: localhost,<hostname(s)|ip address(es)>
   port: 27018
replication:
   replSetName: shardA
sharding:
   clusterRole: shardsvr

mongod --config <path/To/ConfigFile>

mongod --port 27018 --replSet shardA --shardsvr

sh.startBalancer()

Additional Information其他信息¶

A sharded collection has an inconsistent index if the collection does not have the exact same indexes (including the index options) on each shard that contains chunks for the collection. 如果一个分片集合在包含集合块的每个分片上没有完全相同的索引（包括索引选项），则该分片集合的索引不一致。Although inconsistent indexes should not occur during normal operations, inconsistent indexes can occur, such as:虽然正常操作期间不应出现不一致的索引，但也可能出现不一致的索引，例如：

• When a user is creating an index with a unique key constraint and one shard contains a chunk with duplicate documents. 当用户创建具有unique键约束的索引时，一个碎片包含一个包含重复文档的区块。In such cases, the create index operation may succeed on the shards without duplicates but not on the shard with duplicates.在这种情况下，创建索引操作可能会在没有重复项的碎片上成功，但在有重复项的碎片上不会成功。
• When a user is creating an index across the shards in a rolling manner but either fails to build the index for an associated shard or incorrectly builds an index with different specification.当用户以滚动方式跨碎片创建索引，但未能为关联碎片创建索引，或错误地使用不同规范创建索引时。

Starting in MongoDB 4.4 (and 4.2.6), the config server primary periodically checks for index inconsistencies across the shards for sharded collections. 从MongoDB 4.4（和4.2.6）开始，配置服务器主服务器会定期检查碎片集合中碎片之间的索引不一致。To configure these periodic checks, see enableShardedIndexConsistencyCheck and shardedIndexConsistencyCheckIntervalMS.要配置这些定期检查，请参阅启用enableShardedIndexConsistencyCheck和shardedIndexConsistencyCheckIntervalMS。

The command serverStatus returns the field shardedIndexConsistency to report on index inconsistencies when run on the config server primary.命令serverStatus返回字段shardedIndexConsistency，以报告在配置服务器主服务器上运行时的索引不一致。

To check if a sharded collection has inconsistent indexes, see Find Inconsistent Indexes across Shards.要检查分片集合是否有不一致的索引，请参阅在分片之间查找不一致的索引。