Rolling Index Builds on Sharded Clusters基于分片群集的滚动索引构建

Unique Indexes唯一索引

To create unique indexes using the following procedure, you must stop all writes to the collection during this procedure.要使用以下过程创建唯一索引，必须在此过程中停止对集合的所有写入。

If you cannot stop all writes to the collection during this procedure, do not use the procedure on this page. 如果在此过程中无法停止对集合的所有写入，请不要使用此页上的过程。Instead, build your unique index on the collection by issuing db.collection.createIndex() on the mongos for a sharded cluster.相反，通过在mongos上为分片集群发出db.collection.createIndex()，在集合上构建您的唯一索引。

Oplog Size大小

Ensure that your oplog is large enough to permit the indexing or re-indexing operation to complete without falling too far behind to catch up. 确保oplog足够大，以允许索引或重新索引操作完成，而不会落后太多而无法赶上。See the oplog sizing documentation for additional information.有关更多信息，请参阅oplog大小调整文档。

A. Stop the Balancer停止平衡器

Connect mongosh to a mongos instance in the sharded cluster, and run sh.stopBalancer() to disable the balancer: 将mongosh连接到分片集群中的mongos实例，并运行sh.stopBalancer()禁用平衡器：[1]

sh.stopBalancer()

To verify that the balancer is disabled, run sh.getBalancerState(), which returns false if the balancer is disabled:要验证平衡器是否已禁用，请运行sh.getBalancerState()，如果平衡器已禁用，则返回false：

sh.getBalancerState()

B. Determine the Distribution of the Collection确定集合的分布

From mongosh connected to the mongos, refresh the cached routing table for that mongos to avoid returning stale distribution information for the collection. 从连接到mongos的mongosh，刷新该mongos缓存的路由表，以避免返回集合的过时分发信息。Once refreshed, run db.collection.getShardDistribution() for the collection you wish to build the index.刷新后，为要构建索引的集合运行db.collection.getShardDistribution()。

For example, if you want to an ascending index on the records collection in the test database:例如，如果要对test数据库中的records集合建立升序索引：

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

The method outputs the shard distribution. 该方法输出分片分布。For example, consider a sharded cluster with 3 shards shardA, shardB, and shardC and the db.collection.getShardDistribution() returns the following:例如，考虑一个具有3个分片shardA、shardB和shardC的分片集群，db.collection.getShardDistribution()返回以下内容：

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

From the output, you only build the indexes for test.records on shardA and shardC.从输出中，您只能在shardA和shardC上构建test.records的索引。

C. Build Indexes on the Shards That Contain Collection Chunks在包含集合块的分片上构建索引

For each shard that contains chunks for the collection, follow the procedure to build the index on the shard.对于包含集合块的每个分片，请按照以下步骤在分片上构建索引。

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

D. Repeat for the Other Affected Shards对其他受影响的分片重复此操作

Once you finish building the index for a shard, repeat C. Build Indexes on the Shards That Contain Collection Chunks for the other affected shards.完成为一个分片构建索引后，重复C.在包含其他受影响分片的集合块的分片上构建索引。

E. Restart the Balancer重新启动平衡器

Once you finish the rolling index build for the affected shards, restart the balancer.完成受影响分片的滚动索引构建后，重新启动平衡器。

Connect mongosh to a mongos instance in the sharded cluster, and run sh.startBalancer(): 将mongosh连接到分片集群中的mongos实例，并运行sh.startBalancer()：[3]

sh.startBalancer()