Adds the SampleDataRequest/Response

This adds the protos for querying any data samples from the SDK.

model/fn-execution/src/main/proto/org/apache/beam/model/fn_execution/v1/beam_fn_api.proto

@@ -109,6 +109,7 @@ message InstructionRequest {
     FinalizeBundleRequest finalize_bundle = 1004;
     MonitoringInfosMetadataRequest monitoring_infos = 1005;
     HarnessMonitoringInfosRequest harness_monitoring_infos = 1006;
+    SampleDataRequest sample = 1007;
 
     // DEPRECATED
     RegisterRequest register = 1000;
@@ -137,12 +138,75 @@ message InstructionResponse {
     FinalizeBundleResponse finalize_bundle = 1004;
     MonitoringInfosMetadataResponse monitoring_infos = 1005;
     HarnessMonitoringInfosResponse harness_monitoring_infos = 1006;
+    SampleDataResponse sample = 1007;
 
     // DEPRECATED
     RegisterResponse register = 1000;
   }
 }
 
+// If supported, the `SampleDataRequest` will respond with a
+// `SampleDataResponse`. The SDK being queried must have the
+// "beam:protocol:data_sampling:v1" capability. Samples are taken from all
+// specified ProcessBundleDescriptor ids and all specified PCollection ids
+// (equivalent to OR clause). An empty list will match everything.
+message SampleDataRequest {
+  // (Optional) The ProcessBundleDescriptor ids to filter for.
+  repeated string process_bundle_descriptor_ids = 1;
+
+  // (Optional) The PCollection ids to filter for.
+  repeated string pcollection_ids = 2;
+}
+
+
+// An element sampled when the SDK is processing a bundle. This is a proto
+// message to allow for additional per-element metadata.
+message SampledElement {
+  // Required. Sampled raw bytes for an element. This is a
+  // single encoded element in the nested context.
+  bytes element = 1;
+
+  // FUTURE WORK: Capture lull detections and exceptions.
+  //
+  // Optional. Present if there was an exception
+  // processing the above element.
+  //
+  // LogEntry exception_entry = 2;
+}
+
+// If supported, the `SampleDataResponse` will contain samples from PCollections
+// based upon the filters specified in the request.
+message SampleDataResponse {
+  message ElementList {
+    // Required. The individual elements sampled from a PCollection.
+    repeated SampledElement elements = 1;
+  }
+
+  // Map from PCollection id to sampled elements.
+  map<string, ElementList> element_samples = 1;
+
+  // FUTURE WORK: Investigate ways of storing multiple interesting types of
+  // sampled elements. There are two ways of accomplishing this:
+  // 1) Maps of typed elements: include multiple maps here with typed element
+  // proto messages, ex.
+  //
+  // message SlowElement {...}
+  // message ErroredElement {...}
+  // map<string, SlowElement> slow_elements
+  // map<string, ErroredElement> errored_elements
+  //
+  // However, this forces an element into a single category. It disallows
+  // classification across multiple characteristics (like a slow and errored
+  // element).
+  //
+  // 2) Compositional types: allow for URN and payloads on the base
+  // SampledElement message for interesting characteristics. The base class
+  // can then be queried for specific URNs. This allows for multiple
+  // attributes on the same element.
+  //
+  // For a longer conversation, see https://github.com/apache/beam/pull/25065.
+}
+
 // A request to provide full MonitoringInfo associated with the entire SDK
 // harness process, not specific to a bundle.
 //

model/pipeline/src/main/proto/org/apache/beam/model/pipeline/v1/beam_runner_api.proto

@@ -1638,6 +1638,13 @@ message StandardProtocols {
     // SDKs ability to store the data in memory reducing the amount of memory
     // used overall.
     STATE_CACHING = 7 [(beam_urn) = "beam:protocol:state_caching:v1"];
+
+    // Indicates that this SDK can sample in-flight elements. These samples can
+    // then be queried using the SampleDataRequest. Samples are uniquely associated
+    // with a PCollection. Meaning, samples are taken for each PCollection
+    // during bundle processing. This is disabled by default and enabled with the
+    // `enable_data_sampling` experiment.
+    DATA_SAMPLING = 8 [(beam_urn) = "beam:protocol:data_sampling:v1"];
   }
 }