Shard cluster management and monitoring

You can scale out a shard cluster by adding new shard servers. You can also change the shard cluster's definition to change where rows or documents are distributed to.

Modifying a shard-cluster and adding or removing shard servers

To modify the servers in a shard cluster, run the cdr change shardCollection command on one of the shard servers. The cdr change shardCollection command performs the following actions:
  1. A new sharding definition is created.
  2. Using the new sharding definition, existing data is distributed across the shard servers.
  3. The original sharding definition is deleted.
Note: You can add new servers, remove existing servers, or modify the sharding definition, but you cannot change the type of sharding definition. A hash-based sharding definition cannot change to an expression-based sharding definition, and an expression-based sharding definition cannot change to a hash-based sharding definition.
The following example shows how to add capacity to a shard cluster that uses a hash-based sharding definition. The original shard cluster was defined with the following command:
cdr define shardCollection collection_1 db_1:john.customers
   --type=delete --key=identifier --strategy=hash --versionCol=version
   g_shard_server_1
   g_shard_server_2
Run the following command to add g_shard_server_3 to the shard cluster:
cdr change shardCollection collection_1 --add g_shard_server_3
The following example shows how to add a new region-specific server to a shard cluster that uses an expression-based sharding definition. The original shard cluster was created with the following command:
cdr define shardCollection collection_2 db_2:john.clients
   --type=delete --key=state --strategy=expression –-versionCol=version
   g_shard_server_1 "IN ('WA','OR')"
   g_shard_server_2 "IN ('CA','NV')"
   g_shard_server_3  remainder
Run the following command to add g_shard_server_4 to the shard cluster:
cdr change shardCollection collection_2 --add
   g_shard_server_4 "IN ('UT','ID')"
A new sharding definition is created. Any rows or documents that have a shard key of UT or ID are moved from g_shard_server_3 to g_shard_server_4, and all future inserts are distributed according to the new sharding definition.

You can remove servers from a shard cluster using the --drop option or entirely replace a sharding definition with the --replace option.

Monitoring a shard cluster

To see the current definition for a shard cluster, you can run the cdr list shardCollection command on one of the shard servers, and specify the definition's name. For example:
cdr list shardCollection my_collection

To see information on the shard cache, run the onstat -g shard command on one of the shard servers.

Stopping data distribution and deleting a sharding definition

To stop data distribution and delete the sharding definition, run the cdr delete shardCollection on one of the shard servers, and specify the definition's name. For example:
cdr delete shardCollection my_collection