[jubrad]

Motivation

We want cluster SKUs that can only run some kinds of work, for example cheap ingest-only sizes for sources. Without enforcement, a cheap size becomes a compute arbitrage vector. This PR lets replica sizes restrict the workload classes their clusters run, and enforces it in the adapter.

Workload classes

• ingest: sources, subsources, tables from sources, webhook sources, COPY FROM.
• sink: sinks.
• compute_maintained: indexes, materialized views, metric sinks, SUBSCRIBE.
• compute_interactive: SELECT, COPY TO, INSERT, UPDATE, DELETE.
• compute_introspection: SELECT and SUBSCRIBE whose dependencies are all system objects, at least one of them per-replica introspection data. Only the target cluster's replicas can answer these, so restricted sizes can still allow debugging. This shares its dependency analysis with auto-routing to mz_catalog_server.

A replica size can list the classes it allows in allowed_workloads in the size configuration. The cluster_family_allowed_workloads system parameter, a JSON object such as {"legacy": ["ingest", "compute_introspection"]}, restricts every size of a family. Sizes and families without an entry allow every class. A malformed parameter value is logged as an error and ignored.

Invariant

Every object on a cluster must have a class allowed by every size the cluster runs or is about to run: its managed size, the target size of an in-flight reconfiguration, its hydration burst size, and each replica's size. Clusters carry no workload property of their own. The invariant is checked:

• when an object is created, in catalog_transact's CreateItem op. Subsources and tables from sources are checked against their ingestion's cluster.
• when a statement runs, at the existing check_cluster_restrictions call sites (coordinator, frontend peek, frontend read-then-write). Statements are classified by an exhaustive match over Plan with no catch-all, so a new plan kind fails to compile until it is classified.
• when replicas are added: CREATE CLUSTER REPLICA, and ALTER CLUSTER changing size, replication factor, managed-ness, or autoscaling strategy.

Objects that predate a restriction keep running, but replica changes onto sizes that do not allow them are rejected. Resizing to an unrestricted size is always allowed, which is the migration path. Internal users and system clusters are exempt.

NOTE: Every INSERT counts as compute_interactive, because whether it reads on the cluster is only known after optimization. On a restricted cluster, users switch clusters to write.

mz_cluster_replica_sizes gains an allowed_workloads text list column with the effective classes from both mechanisms. It is repacked from the implications phase when cluster_family_allowed_workloads changes. Adding the column needs a Replacement builtin schema migration step, which loses nothing because the table is repacked from the size configuration at every boot.

Tests

• New test/testdrive/cluster-workload-restrictions.td, using new ingest-only and no-ingest sizes in the mzcompose size map. It covers each class being rejected and allowed, introspection queries and subscribes on a restricted cluster, data flowing from an ingest-only cluster, the internal-user exemption, the replica, ALTER CLUSTER, and hydration-size checks, resizing away from a restricted size, the family parameter, and the allowed_workloads column tracking it.
• ReplicaAllocation deserialization test for allowed_workloads.
• Updated expected output for the new column in autogenerated/mz_catalog.slt, mz_catalog_server_index_accounting.slt, and system-cluster.slt.
• cluster_family_allowed_workloads is pinned to {} in mzcompose, because the sqllogictest and TestHarness sizes are all in the legacy family. Parallel workload varies it between {} and {"legacy": ["ingest", "compute_introspection"]}, since it only uses cc sizes.

Release notes

This release will add an allowed_workloads column to mz_cluster_replica_sizes. Clusters whose replica sizes restrict workload classes reject objects and statements of other classes.

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