feat(datastore): Update default channel pool configs to handle initial bursts and scalability

java-datastore/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreOptions.java

@@ -18,8 +18,8 @@
 
 import static com.google.cloud.datastore.Validator.validateNamespace;
 
-import com.google.api.core.ApiFunction;
 import com.google.api.core.BetaApi;
+import com.google.api.core.ObsoleteApi;
 import com.google.api.gax.grpc.ChannelPoolSettings;
 import com.google.api.gax.grpc.InstantiatingGrpcChannelProvider;
 import com.google.api.gax.rpc.TransportChannelProvider;
@@ -37,7 +37,6 @@
 import com.google.cloud.http.HttpTransportOptions;
 import com.google.common.base.MoreObjects;
 import com.google.common.collect.ImmutableSet;
-import io.grpc.ManagedChannelBuilder;
 import java.io.IOException;
 import java.lang.reflect.Method;
 import java.util.Objects;
@@ -54,9 +53,18 @@ public class DatastoreOptions extends ServiceOptions<Datastore, DatastoreOptions
   private static final String DEFAULT_DATABASE_ID = "";
   public static final String PROJECT_ID_ENV_VAR = "DATASTORE_PROJECT_ID";
   public static final String LOCAL_HOST_ENV_VAR = "DATASTORE_EMULATOR_HOST";
-  public static final int INIT_CHANNEL_COUNT = 1;
+  public static final int INIT_CHANNEL_COUNT = 5;
+  static final int CHANNEL_POOL_DEFAULT_RESIZE_DELTA = 5;
+  // Configure this default to be 100 to match the typical default `MAX_CONCURRENT_STREAMS`.
+  // Larger values *may* experience possible client-side queueing as excess streams cannot be
+  // multiplexed onto a full Http2 connection.
+  static final int CHANNEL_POOL_MAX_RPCS_PER_CHANNEL = 100;
   public static final int MIN_CHANNEL_COUNT = 1;
-  public static final int MAX_CHANNEL_COUNT = 4;
+
+  // This is a default max channel constant value set to handle the default initial channel
+  // count and resize delta.
+  @ObsoleteApi("This constant is obsolete and will be removed in a future version")
+  public static final int MAX_CHANNEL_COUNT = 10;
 
   private transient TransportChannelProvider channelProvider = null;
 
@@ -233,33 +241,29 @@ private DatastoreOptions(Builder builder) {
           "Only gRPC transport allows setting of channel provider or credentials provider");
     } else if (getTransportOptions() instanceof GrpcTransportOptions) {
       if (builder.channelProvider == null) {
-        /*
-         The default gRPC connection pool is configured with a minimum of 1 channel.
-         The maximum channel count automatically defaults to 200 (Defined in gax-grpc).
-        */
+        // Set the default gRPC connection pool to be configured with a minimum of 1 channel.
+        // The maximum channel count automatically defaults to 200 (as defined in gax-grpc).
+        // Datastore sets the initial channel pool count to be 5 channels to allow better handle
+        // large loads of requests and the resize delta to be 5 to scale quicker. In cases of low
+        // load, the channel count will scale down as needed and memory will be freed. The default
+        // configuration is set to try and handle ~500 QPS and will scale up and down as needed.
         ChannelPoolSettings datastoreChannelPoolSettings =
             ChannelPoolSettings.builder()
                 .setInitialChannelCount(INIT_CHANNEL_COUNT)
                 .setMinChannelCount(MIN_CHANNEL_COUNT)
+                .setMaxRpcsPerChannel(CHANNEL_POOL_MAX_RPCS_PER_CHANNEL)
+                .setMaxResizeDelta(CHANNEL_POOL_DEFAULT_RESIZE_DELTA)
                 .build();
 
-        ApiFunction<ManagedChannelBuilder, ManagedChannelBuilder> channelConfigurator =
-            this.traceUtil.getChannelConfigurator();
-        if (channelConfigurator == null) {
-          this.channelProvider =
-              GrpcTransportOptions.setUpChannelProvider(
-                  DatastoreSettings.defaultGrpcTransportProviderBuilder()
-                      .setChannelPoolSettings(datastoreChannelPoolSettings),
-                  this);
-        } else {
+        InstantiatingGrpcChannelProvider.Builder channelProviderBuilder =
+            DatastoreSettings.defaultGrpcTransportProviderBuilder()
+                .setChannelPoolSettings(datastoreChannelPoolSettings)
+                .setEndpoint(getHost());
+        if (traceUtil.getChannelConfigurator() != null) {
           // Intercept the grpc channel calls to add telemetry info.
-          this.channelProvider =
-              GrpcTransportOptions.setUpChannelProvider(
-                  DatastoreSettings.defaultGrpcTransportProviderBuilder()
-                      .setChannelPoolSettings(datastoreChannelPoolSettings)
-                      .setChannelConfigurator(channelConfigurator),
-                  this);
+          channelProviderBuilder.setChannelConfigurator(traceUtil.getChannelConfigurator());
         }
+        this.channelProvider = channelProviderBuilder.build();
       } else {
         this.channelProvider = builder.channelProvider;
       }

java-datastore/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/v1/GrpcDatastoreRpc.java

@@ -24,7 +24,6 @@
 import com.google.api.core.InternalApi;
 import com.google.api.gax.core.BackgroundResource;
 import com.google.api.gax.core.GaxProperties;
-import com.google.api.gax.grpc.ChannelPoolSettings;
 import com.google.api.gax.grpc.GrpcCallContext;
 import com.google.api.gax.grpc.GrpcTransportChannel;
 import com.google.api.gax.rpc.ClientContext;
@@ -80,14 +79,11 @@ public GrpcDatastoreRpc(DatastoreOptions datastoreOptions) throws IOException {
           DatastoreStubSettings.newBuilder(clientContext)
               .applyToAllUnaryMethods(retrySettingSetter(datastoreOptions));
       if (!isEmulator(datastoreOptions)) {
+        // Use the TransportChannelProvider configured in DatastoreOptions. For gRPC transport, this
+        // will
+        // be configured with a default ChannelPool configuration
         datastoreStubSettingsBuilder.setTransportChannelProvider(
-            DatastoreSettings.defaultGrpcTransportProviderBuilder()
-                .setChannelPoolSettings(
-                    ChannelPoolSettings.builder()
-                        .setInitialChannelCount(DatastoreOptions.INIT_CHANNEL_COUNT)
-                        .setMinChannelCount(DatastoreOptions.MIN_CHANNEL_COUNT)
-                        .build())
-                .build());
+            datastoreOptions.getTransportChannelProvider());
       }
 
       datastoreStub = GrpcDatastoreStub.create(datastoreStubSettingsBuilder.build());

java-datastore/google-cloud-datastore/src/test/java/com/google/cloud/datastore/DatastoreOptionsTest.java

@@ -187,6 +187,9 @@ public void testGrpcDefaultChannelConfigurations() {
     assertEquals(channelPoolSettings.getInitialChannelCount(), DatastoreOptions.INIT_CHANNEL_COUNT);
     assertEquals(channelPoolSettings.getMinChannelCount(), DatastoreOptions.MIN_CHANNEL_COUNT);
     assertEquals(channelPoolSettings.getMaxChannelCount(), DEFAULT_MAX_CHANNEL_COUNT);
+    assertEquals(
+        channelPoolSettings.getMaxRpcsPerChannel(),
+        DatastoreOptions.CHANNEL_POOL_MAX_RPCS_PER_CHANNEL);
   }
 
   @Test