Databases in a Causal Cluster

Multiple databases in a Causal Cluster are managed the same way as a single instance. Administrators can use the same Cypher commands described in Administrative commands to manage databases. This is based on two main principles:

All databases are available on all members of a cluster - this applies to Core servers and Read Replicas.
Administrative commands must be executed on the system database, on the Leader member of the cluster.

Change the default database

You can use the procedure dbms.cluster.setDefaultDatabase("newDefaultDatabaseName") to change the default database of a Causal cluster.

Ensure that the database to be set as default exists, otherwise create it using the command CREATE DATABASE <database-name>.
Show the name and status of the current default database by using the command SHOW DEFAULT DATABASE.
Stop the current default database using the command STOP DATABASE <database-name>.
On the Leader member of the cluster, run CALL dbms.cluster.setDefaultDatabase("newDefaultDatabaseName") against the system database to set the new default database.
On each cluster member:
1. Open the <neo4j-home>/conf/neo4j.conf file and update the value of dbms.default_database to the new default database.
2. Restart the instance.
Optionally, you can start the previous default database as non-default by using START DATABASE <database-name>.

Run Cypher administrative commands from Cypher Shell on a Causal Cluster

For the following examples consider a Causal Cluster environment formed by 5 members, 3 Core servers, and 2 Read Replicas:

Example 1. View the members of a Causal Cluster

neo4j@neo4j> CALL dbms.cluster.overview();

+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id        | addresses                                                                    | databases                   | groups |
+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| "8c...3d" | ["bolt://localhost:7683", "http://localhost:7473", "https://localhost:7483"] | {neo4j: "FOLLOWER", system: "FOLLOWER"}         | []     |
| "8f...28" | ["bolt://localhost:7681", "http://localhost:7471", "https://localhost:7481"] | {neo4j: "LEADER", system: "LEADER"}                   | []     |
| "e0...4d" | ["bolt://localhost:7684", "http://localhost:7474", "https://localhost:7484"] | {neo4j: "READ_REPLICA", system: "READ_REPLICA"}     | []     |
| "1a...64" | ["bolt://localhost:7682", "http://localhost:7472", "https://localhost:7482"] | {neo4j: "FOLLOWER", system: "FOLLOWER"}         | []     |
| "59...87" | ["bolt://localhost:7685", "http://localhost:7475", "https://localhost:7485"] | {neo4j: "READ_REPLICA", system: "READ_REPLICA"}     | []     |
+------------------------------------------------------------------------------------------------------------------------------------------------------------+

5 rows available after 5 ms, consumed after another 0 ms

The leader is currently the instance exposing port 7681 for the bolt protocol, and 7471/7481 for the http/https protocol.

Administrators can connect and execute Cypher commands in the following ways:

Example 2. Using the bolt:// scheme to connect to the Leader:

$ bin/cypher-shell -a bolt://localhost:7681 -d system -u neo4j -p neo4j1

Connected to Neo4j 4.0.0 at bolt://localhost:7681 as user neo4j.
Type :help for a list of available commands or :exit to exit the shell.
Note that Cypher queries must end with a semicolon.

neo4j@system> SHOW DATABASES;

+-------------------------------+
| name     | status   | default |
+-------------------------------+
| "neo4j"  | "online" | TRUE    |
| "system" | "online" | FALSE   |
+-------------------------------+

2 rows available after 34 ms, consumed after another 0 ms

neo4j@system> CREATE DATABASE data001;

0 rows available after 378 ms, consumed after another 12 ms
Added 1 nodes, Set 4 properties, Added 1 labels
neo4j@system> SHOW DATABASES;
+--------------------------------+
| name      | status   | default |
+--------------------------------+
| "neo4j"   | "online" | TRUE    |
| "system"  | "online" | FALSE   |
| "data001" | "online" | FALSE   |
+--------------------------------+

3 rows available after 2 ms, consumed after another 1 ms

Example 3. Using the neo4j:// scheme to connect to any Core member:

$ bin/cypher-shell -a neo4j://localhost:7683 -d system -u neo4j -p neo4j1

Connected to Neo4j 4.0.0 at neo4j://localhost:7683 as user neo4j.
Type :help for a list of available commands or :exit to exit the shell.
Note that Cypher queries must end with a semicolon.

neo4j@system> SHOW DATABASES;

+--------------------------------+
| name      | status   | default |
+--------------------------------+
| "neo4j"   | "online" | TRUE    |
| "system"  | "online" | FALSE   |
| "data001" | "online" | FALSE   |
+--------------------------------+

3 rows available after 0 ms, consumed after another 0 ms

neo4j@system> CREATE DATABASE data002;

0 rows available after 8 ms, consumed after another 1 ms
Added 1 nodes, Set 4 properties, Added 1 labels

neo4j@system> SHOW DATABASES;

+--------------------------------+
| name      | status   | default |
+--------------------------------+
| "neo4j"   | "online" | TRUE    |
| "system"  | "online" | FALSE   |
| "data001" | "online" | FALSE   |
| "data002" | "online" | FALSE   |
+--------------------------------+

4 rows available after 33 ms, consumed after another 0 ms

The neo4j:// scheme is the equivalent to the bolt+routing: scheme available in earlier versions of Neo4j, but it can be used seamlessly with a standalone and clustered DBMS.