Remove Shards from the existing Sharded cluster


Important points to be considered  before removing the shard from the existing shard cluster

  • Make sure that the shard data is migrated to the other shards successfully.
  • Make sure the balancer is enabled before you run the remove shard.


Step-1: find the shard name to be removed 

To find the name of the shard, connect to mongos instance. 

db.adminCommand( { listShards: 1 } )


Output:

mongos> db.adminCommand( { listShards: 1 } )

{

"shards" : [

{

"_id" : "replicaset1",

"host" : "replicaset1/mysql8.localdomain:27011,mysql8.localdomain:27012,mysql8.localdomain:27013",

"state" : 1

},

{

"_id" : "replicaset2",

"host" : "replicaset2/mysql8.localdomain:27021,mysql8.localdomain:27022,mysql8.localdomain:27023",

"state" : 1

},

{

"_id" : "replicaset3",

"host" : "replicaset3/mysql8.localdomain:27031,mysql8.localdomain:27032,mysql8.localdomain:27033",

"state" : 1

}

],

"ok" : 1,

"operationTime" : Timestamp(1603537651, 1),

"$clusterTime" : {

"clusterTime" : Timestamp(1603537651, 1),

"signature" : {

"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

"keyId" : NumberLong(0)

}

}

}


Step-2: Remove Chunks from the Shard

db.adminCommand( { removeShard: "replicaset1" } )

Note

login the admin database and run the removeShard command. This will start the "draining" chunks to the others chunk from the shard which you will remove in the cluster. The balancer begins migrating chunks from the shard to the other shards in the cluster. The migrations takes place slowly to avoid any load on all other clusters. 

Depending on the network capacity and the amount of data, this operation can take from minutes to days as well to complete.

The operation will return the prompt immediately.


Output:

mongos> db.adminCommand( { removeShard: "replicaset1" } )

{

"msg" : "draining started successfully",

"state" : "started",

"shard" : "replicaset1",

"note" : "you need to drop or movePrimary these databases",

"dbsToMove" : [

"school"

"college"

],

"ok" : 1,

"operationTime" : Timestamp(1603687180, 2),

"$clusterTime" : {

"clusterTime" : Timestamp(1603687180, 2),

"signature" : {

"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

"keyId" : NumberLong(0)

}

}

}


Step-3: Check the migration status 

db.adminCommand( { removeShard: "replicaset1" } )


Output: 

mongos> db.adminCommand( { removeShard: "replicaset1" } )

{

"msg" : "removeshard completed successfully",  <------------------ complete successfully

"state" : "completed",

"shard" : "replicaset1",

"ok" : 1,

"operationTime" : Timestamp(1603687688, 2),

"$clusterTime" : {

"clusterTime" : Timestamp(1603687688, 2),

"signature" : {

"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

"keyId" : NumberLong(0)

}

}

}


Step-4: validate the list of shards post remove successfully

db.adminCommand( { listShards: 1 } )


Output:

You could observe the shard name "replicaset01" is not listed in the below result. So, we have successfully removed the Shard.

mongos> db.adminCommand( { listShards: 1 } )

{

"shards" : [

{

"_id" : "replicaset2",

"host" : "replicaset2/mysql8.localdomain:27021,mysql8.localdomain:27022,mysql8.localdomain:27023",

"state" : 1

},

{

"_id" : "replicaset3",

"host" : "replicaset3/mysql8.localdomain:27031,mysql8.localdomain:27032,mysql8.localdomain:27033",

"state" : 1

}

],

"ok" : 1,

"operationTime" : Timestamp(1603687785, 1),

"$clusterTime" : {

"clusterTime" : Timestamp(1603687785, 1),

"signature" : {

"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

"keyId" : NumberLong(0)

}

}

}


Step-5: Move Databases to Another Primary Shard

If the removed shard was the primary shard of the databases in the cluster, then you should make that database use a different shard as its primary shard. 

If the shard is not the primary shard for any databases, skip the step-5 and Finalize the Migration.


db.adminCommand( { movePrimary: "school", to: "replicaset2" })

Note: This command does not return the prompt until it completes moving all data successfully.


Step-6: Finalize the Migration

db.adminCommand( { removeShard: "replicaset1" } )


Note: look at the state filed and that should show as "completed".

Comments

Post a Comment

Popular posts from this blog

Auditing in Oracle database

Unified Auditing: Oracle Database 12c Release 1 introduces a new auditing feature called Unified Auditing (12.1). Oracle Unified Auditing modifies the database's fundamental auditing capabilities. In earlier versions of Oracle, each component has its own audit trail. With unified auditing, all auditing is compiled into a single repository and view. Due to the fact that all audit data is now in a single location and a single format, there is a double simplification as a result. This data is made available in a consistent format in the UNIFIED AUDIT TRAIL data dictionary view, which is made possible by the unified audit trail, which is stored in a read-only table in the AUDSYS schema in the SYSAUX tablespace.  DBAs can build audit rules and then assign them to various users using Oracle 12c Unified Auditing, which has the same advantages as giving users varying system capabilities based on their responsibilities. The unified_audit_trail database will contain all of the audit records....
Read more

rs.stepDown() in MongoDB replication

It instructs the primary of the replica set to become a secondary. After the primary steps down,the eligible secondaries will hold an election for primary. Generally, the rs.stepDown() does not immediately step down the primary. If no electable secondaries are up to date with the primary, the primary waits up to secondaryCatchUpPeriodSecs (by default 10 seconds)  for a secondary to catch up. Once an electable secondary is available, the method steps down the priamry.  Once stepped down, the original primary becomes a secondary and is ineligible from becoming primary again for the remainder of time specified by stepDownSecs. The rs.stepDown() method attempts to terminate long-running user's operations that block the primary from stepping down, such as an index build, a write operation, or a map-reduce job. Syntax: rs.stepDown(stepDownSecs, secondaryCatchUpPeriodSecs)
Read more

Tuples in Python

 Tuples Basically Tuples in Python are very similar to Lists, but, Tuples are immutable which means that they can not be modified/changed. We generally use Tuples to make sure the values are not changed like, dates, Year, and days of the week or dates on a Calendar.  Creating a Tuple: >>> my_t1=(1,2,3) >>> my_t2=('one','two','three') >>> my_t1 (1, 2, 3) >>> my_t2 ('one', 'two', 'three') -- check the length of tupple: >>> len(my_t1) 3 >>> len(my_t2) 3 -- Tuples can have mixed objects as like Lists. >>> my_t3=(1,'two',3,'four') >>> my_t3 (1, 'two', 3, 'four') -- indexing with tuples  >>> my_t3=(1,'two',3,'four') >>> my_t3[2] 3 Immutable Tuples We can not modify the value. Here is the example: >>> my_t3=(1,'two',3,'four') >>> my_t3[2]=4 Traceback (most recent call last):  ...
Read more