Shard Replica Management

tip

Only Enterprise Edition supports

Replica management is crucial for online services, CnosDB provides the following replica management related commands:

• View Replica Distribution
• Increase Replica
• Delete Replica
• Promote Node to Master
• Destroy Replica Group

For concepts related to replicas and sharding, please refer to Data Sharding and Replication

View Replica Distribution

show replicas

show replicas returns information related to replication groups, including which nodes they are distributed on, start and end times, the name of the associated database, etc., as shown below:

my_db ❯ show replicas;
+------------+----------+--------------+-------------------------+-------------------------+
| replica_id | location | database     | start_time              | end_time                |
+------------+----------+--------------+-------------------------+-------------------------+
| 2          | 1001*    | usage_schema | 2023-12-19 00:00:00 UTC | 2024-12-18 00:00:00 UTC |
| 5          | 1001*    | my_db        | 2022-11-02 23:00:00 UTC | 2022-11-03 07:20:00 UTC |
+------------+----------+--------------+-------------------------+-------------------------+

The node ID where the main node of the replica group is located is identified by *.

Increase Replica

replica add

replica add Add a replica to the specified node in the replication group as shown below:

my_db ❯ replica add replica_id 5 node_id 2001;
Query took 0.058 seconds.

my_db ❯ show replicas;
+------------+------------+--------------+-------------------------+-------------------------+
| replica_id | location   | database     | start_time              | end_time                |
+------------+------------+--------------+-------------------------+-------------------------+
| 2          | 1001*      | usage_schema | 2023-12-19 00:00:00 UTC | 2024-12-18 00:00:00 UTC |
| 5          | 1001*,2001 | my_db        | 2022-11-02 23:00:00 UTC | 2022-11-03 07:20:00 UTC |
+------------+------------+--------------+-------------------------+-------------------------+

A replica was added to Group 5 at node 2001; the primary node is 1001, and the secondary node is 2001

Promote Node to Master

replica promote

Promote a replica to be a master node with replica promote command, which may be useful during machine replacement or other operation and maintenance processes, as shown below:

my_db ❯ replica promote replica_id 5 node_id 2001;
Query took 0.854 seconds.

my_db ❯ show replicas;
+------------+------------+--------------+-------------------------+-------------------------+
| replica_id | location   | database     | start_time              | end_time                |
+------------+------------+--------------+-------------------------+-------------------------+
| 2          | 1001*      | usage_schema | 2023-12-19 00:00:00 UTC | 2024-12-18 00:00:00 UTC |
| 5          | 1001,2001* | my_db        | 2022-11-02 23:00:00 UTC | 2022-11-03 07:20:00 UTC |
+------------+------------+--------------+-------------------------+-------------------------+
Query took 0.010 seconds.

Promote Replica group 5 to be the primary node in node 2001; the primary node becomes 2001, and 1001 becomes the secondary node

Delete Replica

replica remove

replica remove remove a replica, both master and slave replicas support deletion; if the deleted node is the master node, a new master will be randomly selected from the remaining nodes as shown below:

my_db ❯ replica remove replica_id 5 node_id 2001;
Query took 0.036 seconds.

my_db ❯ show replicas;
+------------+----------+--------------+-------------------------+-------------------------+
| replica_id | location | database     | start_time              | end_time                |
+------------+----------+--------------+-------------------------+-------------------------+
| 2          | 1001*    | usage_schema | 2023-12-19 00:00:00 UTC | 2024-12-18 00:00:00 UTC |
| 5          | 1001*    | my_db        | 2022-11-02 23:00:00 UTC | 2022-11-03 07:20:00 UTC |
+------------+----------+--------------+-------------------------+-------------------------+
Query took 0.011 seconds.

Delete replica group 5 in 2001 backup, remaining replica automatically become master nodes

[If only one copy is not allowed to be deleted, you can achieve the deletion purpose by destroying the replication group below]

Destroy Replica Group

replica destory

replica destory destroys the entire replica set as follows:

my_db ❯ replica destory replica_id 5;
Query took 0.027 seconds.

my_db ❯ show replicas;
+------------+----------+--------------+-------------------------+-------------------------+
| replica_id | location | database     | start_time              | end_time                |
+------------+----------+--------------+-------------------------+-------------------------+
| 2          | 1001*    | usage_schema | 2023-12-19 00:00:00 UTC | 2024-12-18 00:00:00 UTC |
+------------+----------+--------------+-------------------------+-------------------------+

Destroy Replica Group 5, if it is a replica with only one copy, deletion can be achieved by destruction