Executing an SQL Statement on All Replication Groups

To execute an SQL statement on all replication groups in the Shardman cluster, run the following command:

shardmanctl [common_options] forall --sql query [--twophase]

Pass the statement to be executed through the --sql option. For shardmanctl to use the two-phase-commit protocol to execute the statement, specify the --twophase option.

Getting the libpq Connection String

To get the libpq connection string for connecting to the cluster as administrator, run the following command:

shardmanctl [common_options] getconnstr [--direct-masters]

If the ClusterSpec.UseProxy configuration parameter is true, by default the connection string referring to proxies is returned. For the returned string to refer to master servers directly, specify the --direct-masters option.

Rebalancing Sharded Tables

If you did not perform rebalance when adding nodes to the cluster or if some other need arises, you can evenly rebalance sharded tables in the cluster. To do this, run the following command:

shardmanctl [common_options] rebalance

Performing Cleanup After Rebalancing

To perform cleanup after a rebalance command failure, run the following command:

shardmanctl [common_options] rebalance_cleanup

On each node, it cleans up subscriptions and publications left from the rebalance command and drops tables that store data of partially-transferred partitions of sharded tables.

Updating the Stolon Configuration

To update the Stolon configuration, run the following command:

shardmanctl [common_options] update [[-f|--file stolon_spec_file]|spec_text [-p|--patch]]

Provide the string with the Stolon configuration as follows:

By default, the new configuration replaces the existing one. To merge the new configuration into the existing one, specify the -p (--patch) option. The new configuration is applied to all replication groups and is saved in clusterdata, so that new replication groups are initialized with this configuration. Note that update can cause a DBMS restart.

Getting the Cluster Connection String

To get the connection string for a Shardman cluster that has the cluster0 name, uses an etcd cluster consisting of n1,n2 and n3 nodes listening on port 2379, run:

 $ shardmanctl --store-endpoints http://n1:2379,http://n2:2379,http://n3:2379 getconnstr
 
 dbname=postgres host=n1,n4,n2,n1,n1,n2,n4,n3 password=yourpasswordhere port=5432,5433,5432,5433,5432,5433,5432,5433 user=postgres
 
 

Executing a Query on All Replication Groups

To execute the “select version()” query on all replication groups, run:

 $ shardmanctl --store-endpoints http://n1:2379,http://n2:2379,http://n3:2379 forall --sql 'select version()'
 
 Node 1 says:
 [PostgreSQL 13.1 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit]
 Node 4 says:
 [PostgreSQL 13.1 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit]
 Node 3 says:
 [PostgreSQL 13.1 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit]
 Node 2 says:
 [PostgreSQL 13.1 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit]
 
 

Performing Rebalance

To rebalance sharded tables in the cluster0 cluster, run:

 $ shardmanctl --store-endpoints http://n1:2379,http://n2:2379,http://n3:2379 rebalance
 

Updating PostgreSQL Configuration Settings

To set the max_connections parameter to 200 in the cluster, create the spec file (for instance, ~/stolon.json) with the following contents:

 {
   "pgParameters": {
     "max_connections": "200"
   }
 }
 

Then run:

 $ shardmanctl --store-endpoints http://n1:2379,http://n2:2379,http://n3:2379 update -p -f ~/stolon.json
 

Since changing max_connections requires a restart, DBMS instances are restarted by this command.