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ClickHouse® Cluster Fault Tolerance

ClickHouse® cluster fault tolerance is affected by:

Data replication

Replication is supported only for replicated tables. Read more about replicated tables in the ClickHouse® documentation Replicated* table engines.

To ensure data replication and enable the creation of replicated tables, the cluster must consist of:

You can specify the number of nodes in a shard when creating a cluster. You can also add or delete nodes in a shard of an existing cluster. The maximum number of nodes in a shard is ten.

If you specify more than one node in a shard when creating a cluster, ClickHouse® Keeper will be added automatically.

To add nodes to an existing cluster consisting of one shard with one node, you must first add ClickHouse® Keeper. When adding ClickHouse® Keeper, existing MergeTree tables are automatically converted to replicated ones (for example, to ReplicatedMergeTree). When new nodes are added to such a cluster, they are automatically synchronized with existing replicas in the shard.

Node allocation type

The node allocation type in a cluster depends on:

You can view the list of pools and segments in the Servercore Infrastructure table of the Locations: countries, regions, availability zones, pools, and data center addresses instruction.

Four node allocation types are available:

  • Single-Segment;
  • Multi-Segment;
  • Single-AZ;
  • Multi-AZ.

ноды размещаются in одном сегменте однозонального пула. применимо:

  • clusters consisting of one shard with one node;
  • shards with multiple nodes, if the cluster is located in a pool that consists of a single segment;
  • shards with multiple nodes in HighFreq configuration lines.
note

For example, you have created a cluster in the ru-2 pool with ClickHouse® Keeper and a shard with two nodes. For both groups of nodes, you used configurations from the HighFreq line. All nodes will be placed in the same pool segment, for example, ru-2c.

Add a node

A shard can have no more than ten nodes. During the node addition process, other nodes in the shard will continue to operate in read/write mode.

  1. If the cluster consists of only one shard with one node, add ClickHouse® Keeper.
  2. In the Dashboard, on the top menu, click Products and select Managed Databases.
  3. Open the Active tab.
  4. Open the cluster page → Settings tab.
  5. In the shard menu , select Change node count.
  6. откройте вкладку добавление.
  7. Specify the new number of nodes in the shard. If there are no free IP addresses in the subnet to which the cluster is connected, you cannot add a node. Each new node occupies a new IP address in the subnet.
  8. Click Save.

Delete a node

carefully

Deleting a node will remove all data located on that node.

During the deletion process, other nodes in the shard will continue to operate in read/write mode. The public IP address assigned to the node will be deleted.

  1. In the Dashboard, click Products on the top menu and select Managed Databases.
  2. откройте вкладку активные.
  3. откройте страницу кластера → вкладка настройки.
  4. In the shard menu , select Change node count.
  5. откройте вкладку удаление.
  6. Select the node you want to delete. At least one node must remain in the shard. You cannot delete all nodes from a shard.
  7. Click Save.

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