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schema_migration.md

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Schema maintenance

clickhouse-operator automates schema management when cluster is scaled up or down

Schema auto-creation

After cluster is scaled up and new ClickHouse instances are ready, clickhouse-operator automatically creates schema.

If shard is added:

  • Other shards in the cluster are analyzed for distributed and corresponding local tables
  • Databases for local and distributed tables are created
  • Local tables are created
  • Distributed tables are created

If replica is added:

  • Other replicas at the same shard are analyzed for replicated tables
  • Databases for replicated tables are created
  • Replicated tables are created
  • Then the same logic as to adding shard applies

Schema auto-deletion

If cluster is scaled down and some shards or replicas are deleted, clickhouse-operator drops replicated table to make sure nothing is left in ZooKeeper.