Ray Knowledge Patch

Ray Knowledge Patch

Use this skill for implementation, migration, debugging, or operations involving Ray Core, Ray Data, Ray Train, Ray Tune, Ray Serve, or KubeRay. Inspect the project's dependency manifests and configuration before applying guidance, and prefer observed project behavior when it differs.

Reference index

Read only the references relevant to the component being changed. For changes that span Data and Train or Serve and KubeRay, read both corresponding files because ownership of execution and recovery settings crosses component boundaries.

Compatibility priorities

Data migration hazards

• Expression filters use compute=; do not use the deprecated concurrency= argument.
• Do not build new code on ConcurrencyCapBackpressurePolicy, DataIterator.to_torch, pandas UDF batches, DataContext.scheduling_strategy, actor_locality_enabled, exclude_resources, or local://.
• read_tfrecords no longer supports tfx-bsl, and cluster autoscaler v1 has been removed.
• DataSource V2 is the default reader path. Account for row-group-aware chunking and predicate splitting when comparing plans or performance.
• read_numpy disallows pickle by default. write_lance(mode=CREATE) fails rather than overwriting an existing target.

See Data processing before updating readers, transforms, conversion code, or storage behavior.

Train and Tune migration hazards

• Train V2 is opt-in through RAY_TRAIN_V2_ENABLED=1; verify V2 imports and APIs instead of carrying forward legacy helpers by assumption.
• Train v1 Predictor is removed. Result.from_path is read-only, and ray.train.report(checkpoint=...) accepts only in-band checkpoints.
• OptunaSearch requires optuna>=3.0.0.
• MultiRLModuleSpec.rl_module_specs must be a dictionary.

Use Training and API stability for dataset, checkpoint, metadata, and API-transition details. Use Tuning for scheduler and search integration constraints.

Serve ingress hazards

• Replace deprecated HTTPOptions.location with proxy_location.
• A nonzero HTTPOptions.num_cpus is rejected.
• Direct ingress rejects an ingress deployment that also uses a custom request router or serve.multiplexed.
• HAProxy ingress expects the separately distributed ray-haproxy package.

Read Serving and recovery before changing ingress, routing, controller, or request-lifecycle configuration.

Core tasks and actors

Preserve actor method types

Keep the implementation class undecorated, mark methods with @ray.method, wrap the class using ray.remote(), and annotate the wrapper and handle with ActorClass[T] and ActorProxy[T]. This carries the method's return type through .remote() to ObjectRef[R].

import ray
from ray.actor import ActorClass, ActorProxy

class Counter:
    @ray.method
    def increment(self) -> int:
        return 1

CounterActor: ActorClass[Counter] = ray.remote(Counter)
counter: ActorProxy[Counter] = CounterActor.remote()
result: ray.ObjectRef[int] = counter.increment.remote()

Treat cancellation as cooperative

ray.cancel() is best-effort. A queued actor task can surface TaskCancelledError, but running regular or threaded actor methods must poll ray.get_runtime_context().is_canceled(). Async actor methods receive asyncio.Task cancellation at an await; do not call is_canceled() inside them. Use recursive=True when tracked child and actor tasks should also be targeted.

Control task-event overhead explicitly

Set enable_task_events=False on remote functions or actors to suppress Dashboard and State API status and profiling events. Nested tasks do not inherit the parent's choice. An actor method setting overrides the actor setting.

See Tasks and actors for actor closures, streaming-generator backpressure, topology-aware placement, embedded GCS storage, and node-drain behavior.

Ray Data

Know where streaming stops

Dataset transformations are lazy. Non-shuffle operators can overlap as a streaming pipeline after consumption starts, while sort() and groupby() must materialize their shuffle before streaming continues.

Select the right transform worker model

• Plain functions use tasks and can be capped with TaskPoolStrategy(size=n).
• Callable classes use actors, initialize once per worker, and default to an autoscaling pool unless configured with ActorPoolStrategy.
• Resource arguments affect logical scheduling; they do not enforce physical CPU, GPU, or memory limits.
• Async transforms require a callable class with async def __call__; async function transforms are unsupported.

GPU transforms require an integer batch_size; reduce it after worker memory errors. batch_size="auto" is available for non-GPU transforms.

Preserve order only when required

Transforms do not preserve block order unless the Dataset is sorted or the current Data context enables execution_options.preserve_order. Enabling it can reduce throughput when workers finish unevenly.

See Data processing for replica placement groups, alpha column expressions, weighted mixing, catalogs, Kafka bounds, worker isolation, retries, conversions, and backpressure controls.

Ray Train

Decide dataset sharding per input

Train normally uses Dataset.streaming_split() so every worker receives a disjoint shard of every Dataset. Set DataConfig(datasets_to_split=[...]) to shard only selected inputs. Each worker sees an unlisted validation Dataset in full; aggregate results across workers when validation is split.

Configure both stages of subcluster placement

Apply a copied DataContext with an execution label selector while constructing the Dataset, then repeat the selector in DataConfig.execution_options for ingestion. Train replaces Dataset execution options, so the construction-time selector alone does not pin worker ingestion.

Carry preprocessors through checkpoints

Fit and apply preprocessing before Trainer construction. Serialize the fitted preprocessor, encode its bytes for the JSON-compatible Trainer metadata, and recover it from checkpoint metadata. Use per-Dataset execution resource limits to backpressure object-store production when consumers lag.

See Training and API stability for examples and the stability and deprecation rules.

Ray Tune

Emit results correctly

A function trainable may call tune.report() for intermediate results, return a dictionary for only its final result, or yield dictionaries for successive results. Class-based Trainable implementations cannot call tune.report().

Bound open-ended searches

Use num_samples=-1 with time_budget_s to generate trials until the wall clock budget expires. A finite num_samples caps trial count.

Match schedulers to checkpointing and search

• ASHA and Median Stopping require no checkpointing and support search algorithms.
• HyperBand requires checkpointing and supports search algorithms.
• BOHB requires checkpointing and only works with TuneBOHB.
• PBT and PB2 require checkpointing and are incompatible with search algorithms.

ResourceChangingScheduler can wrap another scheduler to change a trial's resource request while tuning. See Tuning for the full matrix and search-library requirements.

Ray Serve

Pipeline deployment responses

A deployment method returns DeploymentResponse immediately. Await it for a local value or pass it directly to another DeploymentHandle call so composed deployments do not materialize intermediate values locally.

Design around recovery boundaries

Application exceptions return HTTP 500 with traceback information without killing the replica. Serve recreates failed replicas, proxies, and the controller and restores persisted controller state from GCS. Transient connections and internal request queues are lost, and whole-cluster recovery belongs at the KubeRay layer.

HTTP, gRPC, and deployment-handle traffic can continue while the controller is down, but autoscaling pauses and resumes without the metrics gathered before failure. Every cluster node exposes a Serve REST management server.

See Serving and recovery for extensible routers, HAProxy and gRPC ingress, controller runtime environments, request timeouts, rolling updates, disconnect handling, and LLM routing modes.

KubeRay

Choose the RayJob submission model deliberately

A RayJob may embed rayClusterSpec to create a cluster or use clusterSelector for an existing one. Submission modes have distinct constraints: K8sJobMode creates a submitter Job, HTTPMode submits through the operator, InteractiveMode waits for the user, and SidecarMode places the submitter in the head Pod.

Keep cluster retries separate from submitter Job retries. Configure pre-running and active deadlines independently, and choose cleanup rules only after deciding whether the cluster and RayJob custom resource should survive.

See Kubernetes operations for bootstrap commands, generated services, submission fields, retry defaults, lifecycle status, cleanup compatibility, suspension, and RayService readiness.