--- title: "CREATE CLUSTER" description: "`CREATE CLUSTER` creates a new cluster." pagerank: 40 menu: main: parent: commands --- `CREATE CLUSTER` creates a new [cluster](/concepts/clusters/). ## Conceptual framework A cluster is a pool of compute resources (CPU, memory, and scratch disk space) for running your workloads. The following operations require compute resources in Materialize, and so need to be associated with a cluster: - Executing [`SELECT`] and [`SUBSCRIBE`] statements. - Maintaining [indexes](/concepts/indexes/) and [materialized views](/concepts/views/#materialized-views). - Maintaining [sources](/concepts/sources/) and [sinks](/concepts/sinks/). ## Syntax {{< diagram "create-managed-cluster.svg" >}} ### Options {{< yaml-table data="syntax_options/create_cluster_options" >}} ## Details ### Initial state Each Materialize region initially contains a [pre-installed cluster](/sql/show-clusters/#pre-installed-clusters) named `quickstart` with a size of `25cc` and a replication factor of `1`. You can drop or alter this cluster to suit your needs. ### Choosing a cluster When performing an operation that requires a cluster, you must specify which cluster you want to use. Not explicitly naming a cluster uses your session's active cluster. To show your session's active cluster, use the [`SHOW`](/sql/show) command: ```mzsql SHOW cluster; ``` To switch your session's active cluster, use the [`SET`](/sql/set) command: ```mzsql SET cluster = other_cluster; ``` ### Resource isolation Clusters provide **resource isolation.** Each cluster provisions a dedicated pool of CPU, memory, and, optionally, scratch disk space. All workloads on a given cluster will compete for access to these compute resources. However, workloads on different clusters are strictly isolated from one another. A given workload has access only to the CPU, memory, and scratch disk of the cluster that it is running on. Clusters are commonly used to isolate different classes of workloads. For example, you could place your development workloads in a cluster named `dev` and your production workloads in a cluster named `prod`. ### Size The `SIZE` option determines the amount of compute resources (CPU, memory, and disk) available to the cluster. Valid sizes are: * `25cc` * `50cc` * `100cc` * `200cc` * `300cc` * `400cc` * `600cc` * `800cc` * `1200cc` * `1600cc` * `3200cc` * `6400cc` * `128C` * `256C` * `512C` The resource allocations are proportional to the number in the size name. For example, a cluster of size `600cc` has 2x as much CPU, memory, and disk as a cluster of size `300cc`, and 1.5x as much CPU, memory, and disk as a cluster of size `400cc`. To determine the specific resource allocations for a size, query the [`mz_cluster_replica_sizes`] table. {{< warning >}} The values in the `mz_cluster_replica_sizes` table may change at any time. You should not rely on them for any kind of capacity planning. {{< /warning >}} Clusters of larger sizes can process data faster and handle larger data volumes. #### Cluster resizing You can change the size of a cluster to respond to changes in your workload using [`ALTER CLUSTER`](/sql/alter-cluster). Depending on the type of objects the cluster is hosting, this operation **might incur downtime**. See the reference documentation for [`ALTER CLUSTER`](/sql/alter-cluster#zero-downtime-cluster-resizing) for more details on cluster resizing. #### Legacy sizes Materialize also offers some legacy sizes. Clusters using legacy sizes run on older hardware without local disks attached. In most cases, you **should not** use legacy sizes. [Standard sizes](#size) offer better performance per credit for nearly all workloads. We recommend using standard sizes for all new clusters, and recommend migrating existing legacy-sized clusters to standard sizes. In many cases, migrating from legacy to standard sizes will result in a 25-50% cost reduction. However, certain rare workloads exhibit better performance per credit on legacy sizes. Materialize is committed to supporting these workloads on legacy sizes until they have equivalent or better performance per credit on standard sizes. {{< if-past "2024-04-15" >}} {{< warning >}} Materialize regions that were enabled after 15 April 2024 do not have access to legacy sizes. {{< /warning >}} {{< /if-past >}} When legacy sizes are enabled for a region, the following sizes are available: * `3xsmall` * `2xsmall` * `xsmall` * `small` * `medium` * `large` * `xlarge` * `2xlarge` * `3xlarge` * `4xlarge` * `5xlarge` * `6xlarge` The correspondence between non-legacy sizes and legacy sizes is shown in the [credit usage table](#credit-usage). ### Replication factor The `REPLICATION FACTOR` option determines the number of replicas provisioned for the cluster. Each replica of the cluster provisions a new pool of compute resources to perform exactly the same computations on exactly the same data. Provisioning more than one replica improves **fault tolerance**. Clusters with multiple replicas can tolerate failures of the underlying hardware that cause a replica to become unreachable. As long as one replica of the cluster remains available, the cluster can continue to maintain dataflows and serve queries. Materialize makes the following guarantees when provisioning replicas: - Replicas of a given cluster are never provisioned on the same underlying hardware. - Replicas of a given cluster are spread as evenly as possible across the underlying cloud provider's availability zones. Materialize automatically assigns names to replicas like `r1`, `r2`, etc. You can view information about individual replicas in the console and the system catalog, but you cannot directly modify individual replicas. You can pause a cluster's work by specifying a replication factor of `0`. Doing so removes all replicas of the cluster. Any indexes, materialized views, sources, and sinks on the cluster will cease to make progress, and any queries directed to the cluster will block. You can later resume the cluster's work by using [`ALTER CLUSTER`] to set a nonzero replication factor. {{< note >}} A common misconception is that increasing a cluster's replication factor will increase its capacity for work. This is not the case. Increasing the replication factor increases the **fault tolerance** of the cluster, not its capacity for work. Replicas are exact copies of one another: each replica must do exactly the same work (i.e., maintain the same dataflows and process the same queries) as all the other replicas of the cluster. To increase a cluster's capacity, you should instead increase the cluster's [size](#size). {{< /note >}} ### Credit usage Each [replica](#replication-factor) of the cluster consumes credits at a rate determined by the cluster's size: Size | Legacy size | Credits per replica per hour ----------|--------------|----------------------------- `25cc` | `3xsmall` | 0.25 `50cc` | `2xsmall` | 0.5 `100cc` | `xsmall` | 1 `200cc` | `small` | 2 `300cc` |   | 3 `400cc` | `medium` | 4 `600cc` |   | 6 `800cc` | `large` | 8 `1200cc` |   | 12 `1600cc` | `xlarge` | 16 `3200cc` | `2xlarge` | 32 `6400cc` | `3xlarge` | 64 `128C` | `4xlarge` | 128 `256C` | `5xlarge` | 256 `512C` | `6xlarge` | 512 Credit usage is measured at a one second granularity. For a given replica, credit usage begins when a `CREATE CLUSTER` or [`ALTER CLUSTER`] statement provisions the replica and ends when an [`ALTER CLUSTER`] or [`DROP CLUSTER`] statement deprovisions the replica. A cluster with a [replication factor](#replication-factor) of zero uses no credits. As an example, consider the following sequence of events: Time | Event --------------------|--------------------------------------------------------- 2023-08-29 3:45:00 | `CREATE CLUSTER c (SIZE '400cc', REPLICATION FACTOR 2`) 2023-08-29 3:45:45 | `ALTER CLUSTER c SET (REPLICATION FACTOR 1)` 2023-08-29 3:47:15 | `DROP CLUSTER c` Cluster `c` will have consumed 0.4 credits in total: * Replica `c.r1` was provisioned from 3:45:00 to 3:47:15, consuming 0.3 credits. * Replica `c.r2` was provisioned from 3:45:00 to 3:45:45, consuming 0.1 credits. ### Scheduling {{< private-preview />}} To support [scheduled refreshes in materialized views](../create-materialized-view/#refresh-strategies), you can configure a cluster to automatically turn on and off using the `SCHEDULE...ON REFRESH` syntax. ```mzsql CREATE CLUSTER my_scheduled_cluster ( SIZE = '3200cc', SCHEDULE = ON REFRESH (HYDRATION TIME ESTIMATE = '1 hour') ); ``` Scheduled clusters should **only** contain materialized views configured with a non-default [refresh strategy](../create-materialized-view/#refresh-strategies) (and any indexes built on these views). These clusters will automatically turn on (i.e., be provisioned with compute resources) based on the configured refresh strategies, and **only** consume credits for the duration of the refreshes. It's not possible to manually turn on a cluster with `ON REFRESH` scheduling. If you need to turn on a cluster outside its schedule, you can temporarily disable scheduling and provision compute resources using [`ALTER CLUSTER`](../alter-cluster/#schedule): ```mzsql ALTER CLUSTER my_scheduled_cluster SET (SCHEDULE = MANUAL, REPLICATION FACTOR = 1); ``` To re-enable scheduling: ```mzsql ALTER CLUSTER my_scheduled_cluster SET (SCHEDULE = ON REFRESH (HYDRATION TIME ESTIMATE = '1 hour')); ``` #### Hydration time estimate

Syntax: HYDRATION TIME ESTIMATE interval

By default, scheduled clusters will turn on at the scheduled refresh time. To avoid [unavailability of the objects scheduled for refresh](/sql/create-materialized-view/#querying-materialized-views-with-refresh-strategies) during the refresh operation, we recommend turning the cluster on ahead of the scheduled time to allow hydration to complete. This can be controlled using the `HYDRATION TIME ESTIMATE` clause. #### Introspection To check the scheduling strategy associated with a cluster, you can query the [`mz_internal.mz_cluster_schedules`](/sql/system-catalog/mz_internal/#mz_cluster_schedules) system catalog table: ```mzsql SELECT c.id AS cluster_id, c.name AS cluster_name, cs.type AS schedule_type, cs.refresh_hydration_time_estimate FROM mz_internal.mz_cluster_schedules cs JOIN mz_clusters c ON cs.cluster_id = c.id WHERE c.name = 'my_refresh_cluster'; ``` To check if a scheduled cluster is turned on, you can query the [`mz_catalog.mz_cluster_replicas`](/sql/system-catalog/mz_catalog/#mz_cluster_replicas) system catalog table: ```mzsql SELECT cs.cluster_id, -- A cluster with scheduling is "on" when it has compute resources -- (i.e. a replica) attached. CASE WHEN cr.id IS NOT NULL THEN true ELSE false END AS is_on FROM mz_internal.mz_cluster_schedules cs JOIN mz_clusters c ON cs.cluster_id = c.id AND cs.type = 'on-refresh' LEFT JOIN mz_cluster_replicas cr ON c.id = cr.cluster_id; ``` You can also use the [audit log](../system-catalog/mz_catalog/#mz_audit_events) to observe the commands that are automatically run when a scheduled cluster is turned on and off for materialized view refreshes: ```mzsql SELECT * FROM mz_audit_events WHERE object_type = 'cluster-replica' ORDER BY occurred_at DESC; ``` Any commands attributed to scheduled refreshes will be marked with `"reason":"schedule"` under the `details` column. ### Known limitations Clusters have several known limitations: * When a cluster of size `3200cc` or larger uses multiple replicas, those replicas are not guaranteed to be spread evenly across the underlying cloud provider's availability zones. We plan to remove these restrictions in future versions of Materialize. ## Examples ### Basic Create a cluster with two `400cc` replicas: ```mzsql CREATE CLUSTER c1 (SIZE = '400cc', REPLICATION FACTOR = 2); ``` ### Introspection disabled Create a cluster with a single replica and introspection disabled: ```mzsql CREATE CLUSTER c (SIZE = '100cc', INTROSPECTION INTERVAL = 0); ``` Disabling introspection can yield a small performance improvement, but you lose the ability to run [troubleshooting queries](/ops/troubleshooting/) against that cluster replica. ### Empty Create a cluster with no replicas: ```mzsql CREATE CLUSTER c1 (SIZE '100cc', REPLICATION FACTOR = 0); ``` You can later add replicas to this cluster with [`ALTER CLUSTER`]. ## Privileges The privileges required to execute this statement are: {{< include-md file="shared-content/sql-command-privileges/create-cluster.md" >}} ## See also - [`ALTER CLUSTER`] - [`DROP CLUSTER`] [AWS availability zone IDs]: https://docs.aws.amazon.com/ram/latest/userguide/working-with-az-ids.html [`ALTER CLUSTER`]: /sql/alter-cluster/ [`DROP CLUSTER`]: /sql/drop-cluster/ [`SELECT`]: /sql/select [`SUBSCRIBE`]: /sql/subscribe [`mz_cluster_replica_sizes`]: /sql/system-catalog/mz_catalog#mz_cluster_replica_sizes