CREATE CLUSTER

CREATE CLUSTER creates a new cluster.

Conceptual framework

A cluster is a pool of compute resources (CPU, memory, and, optionally, 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 and materialized views.
Maintaining sources and sinks.

Syntax

Options

Field	Value	Description
`SIZE`	`text`	The size of the resource allocations for the cluster. See Size for details.
`REPLICATION FACTOR`	`text`	The number of replicas to provision for the cluster. See Replication factor for details. Default: `1`
`INTROSPECTION INTERVAL`	`interval`	The interval at which to collect introspection data. See Troubleshooting for details about introspection data. The special value `0` entirely disables the gathering of introspection data. Default: `1s`
`INTROSPECTION DEBUGGING`	`bool`	Indicates whether to introspect the gathering of the introspection data. Default: `FALSE`
`IDLE ARRANGEMENT MERGE EFFORT`	`integer`	Unstable. This option may be changed or removed at any time. The amount of effort the replica should exert on compacting arrangements during idle periods.
`DISK`	`bool`	Private preview. This option has known performance or stability issues and is under active development. Whether to attach a disk to the cluster. See Disk for details. Default: `FALSE`
`MANAGED`	`bool`	Whether to automatically manage the cluster’s replicas based on the configured size and replication factor. If `FALSE`, enables the use of the deprecated `CREATE CLUSTER REPLICA` command. Default: `TRUE`

Details

Initial state

Each Materialize region initially contains a cluster named default with a size of xsmall 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 command:

SHOW cluster;

To switch your session’s active cluster, use the SET command:

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:

3xsmall
2xsmall
xsmall
small
medium
large
xlarge
2xlarge
3xlarge
4xlarge
5xlarge
6xlarge

Clusters of larger sizes can process data faster and handle larger data volumes. You can use ALTER CLUSTER to resize the cluster in order to respond to changes in the resource requirements of your workload.

The resource allocations for a given size are twice the resource allocations of the previous size. To determine the specific resource allocations for a size, query the mz_internal.mz_cluster_replica_sizes table.

WARNING! The values in the mz_internal.mz_cluster_replica_sizes table may change at any time. You should not rely on them for any kind of capacity planning.

Disk

PREVIEW This feature is in private preview. It has known performance or stability issues and is under active development. It isn't subject to our backwards compatibility guarantees.

You must contact us to enable this feature in your Materialize region.

WARNING!

Pricing for this feature is likely to change.

Clusters with disks currently consume credits at the same rate as clusters without disks. In the future, clusters with disks will likely consume credits at a faster rate than clusters without disks.

The DISK option attaches a scratch disk to the cluster.

Attaching a disk allows you to trade off performance for cost. A cluster of a given size has access to several times more disk than memory, allowing the processing of larger data sets at that replica size. Operations on a disk, however, are much slower than operations in memory, and so a workload that spills to disk will perform more slowly than a workload that does not. Note that exact storage medium for the attached disk is not specified, and its performance characteristics are subject to change.

Consider attaching a disk to clusters that contain sources that use the upsert envelope or the Debezium envelope. When you place these sources on a cluster with an attached disk, they will automatically spill state to disk. These sources will therefore use less memory but may ingest data more slowly. See Sizing a source for details.

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.

Credit usage

Each replica of the cluster consumes credits at a rate determined by the cluster’s size:

Size	Credits per replica per hour
3xsmall	0.25
2xsmall	0.5
xsmall	1
small	2
medium	4
large	8
xlarge	16
2xlarge	32
3xlarge	64
4xlarge	128
5xlarge	256
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 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 'medium', 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.

Known limitations

Clusters have several known limitations:

Clusters containing sources and sinks can only have a replication factor of 0 or 1.
A given cluster may contain any number of indexes and materialized views or any number of sources and sinks, but not both types of objects. For example, you may not create a cluster with a source and an index.
You cannot run SELECT or SUBSCRIBE statements on a cluster containing sources or sinks.
When a cluster of size 2xlarge 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 medium replicas:

CREATE CLUSTER c1 SIZE = 'medium', REPLICATION FACTOR = 2;

Introspection disabled

Create a cluster with a single replica and introspection disabled:

CREATE CLUSTER c SIZE = 'xsmall', INTROSPECTION INTERVAL = 0;

Disabling introspection can yield a small performance improvement, but you lose the ability to run troubleshooting queries against that cluster replica.

Empty

Create a cluster with no replicas:

CREATE CLUSTER c1 SIZE 'xsmall', REPLICATION FACTOR = 0;

You can later add replicas to this cluster with ALTER CLUSTER.

Privileges

The privileges required to execute this statement are:

CREATECLUSTER privileges on the system.