Clickhouse fixes for cluster operation

[Chris3LC]

I tried to make the clickhouse community plugin work on our setup, but had to make a few changes:

• Adding "ON CLUSTER" to DDL's, to have the changes reproduced on all nodes.
• Adding a systemConnection in ClickHouseDatabase - this one is a bit surprising to me, but I got a "Database the_database doesn't exist" error when executing jdbcTemplate.queryForInt("SELECT COUNT() FROM system.tables WHERE database = ?", name). Even though I am not accessing the_database, the connection is configured to use it, so I get an exception.
• Using getCatalog instead of getSchema. This is kinda optional, but it appears that with clickhouse-jdbc:0.5.0 and newer versions, catalog is used instead of schema (can be overridden using ?databaseTerm=schema in the jdbc-url).

Each change is in a separate commit.

[Chris3LC]

@sazonov Could you please review this change?

This is approximately the setup we used to run it (kotlin):

    Flyway(
        Flyway.configure()
            .dataSource(
                "jdbc:clickhouse://localhost:9001/", // change port to 9002, 9003, 9004 for the other nodes of the cluster
                "admin",
                "123"
            )
            .configuration(mapOf(
                "flyway.clickhouse.clusterName" to "'{cluster}'",
                // don't put {shard} in the zookeeperPath, to have the change replicated (and visible) on all nodes
                "flyway.clickhouse.zookeeperPath" to "/clickhouse/tables/{database}/{table}",
            ))
            .placeholders(mapOf("database" to "the_database"))
            .schemas("the_database")
            .createSchemas(true)
            .failOnMissingLocations(true)
            .locations("clickhouse/migrations")
            .table("flyway_history")
            .baselineVersion("0000")
            .baselineOnMigrate(true)
    ).migrate()

I tested using following docker-compose cluster: https://github.com/Chris3LC/clickhouse-cluster

[sazonov]

I tested this on single node and cluster instances. It works well, thanks for the fixes.

[sazonov]

@Barry-RG those are critical fixes.

[Barry-RG]

Thanks @Chris3LC and @sazonov for looking at this