feat: Improve upon the default gRPC Connection Pool size (#1706)

* feat: Improve upon the default gRPC Connection Pool size

* feat: Improve upon the default gRPC Connection Pool size

* fix formatting

* add comment

* Add test

* formatting

* Add constants for min, max and init channel count

* Fix ci testing environment with java 11

* Revert "Fix ci testing environment with java 11"

This reverts commit 00c0d21.

Author: cindy-peng

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

@@ -19,6 +19,7 @@
 import static com.google.cloud.datastore.Validator.validateNamespace;
 
 import com.google.api.core.BetaApi;
+import com.google.api.gax.grpc.ChannelPoolSettings;
 import com.google.api.gax.grpc.InstantiatingGrpcChannelProvider;
 import com.google.api.gax.rpc.TransportChannelProvider;
 import com.google.cloud.ServiceDefaults;
@@ -50,6 +51,9 @@ 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 MIN_CHANNEL_COUNT = 1;
+  public static final int MAX_CHANNEL_COUNT = 4;
 
   private transient TransportChannelProvider channelProvider = null;
 
@@ -218,11 +222,20 @@ private DatastoreOptions(Builder builder) {
       throw new IllegalArgumentException(
           "Only gRPC transport allows setting of channel provider or credentials provider");
     } else if (getTransportOptions() instanceof GrpcTransportOptions) {
+      // For grpc transport options, configure default gRPC Connection pool with minChannelCount = 1
+      // and maxChannelCount = 4
       this.channelProvider =
           builder.channelProvider != null
               ? builder.channelProvider
               : GrpcTransportOptions.setUpChannelProvider(
-                  DatastoreSettings.defaultGrpcTransportProviderBuilder(), this);
+                  DatastoreSettings.defaultGrpcTransportProviderBuilder()
+                      .setChannelPoolSettings(
+                          ChannelPoolSettings.builder()
+                              .setInitialChannelCount(INIT_CHANNEL_COUNT)
+                              .setMinChannelCount(MIN_CHANNEL_COUNT)
+                              .setMaxChannelCount(MAX_CHANNEL_COUNT)
+                              .build()),
+                  this);
     }
   }
 

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

@@ -24,6 +24,7 @@
 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;
@@ -74,9 +75,19 @@ public GrpcDatastoreRpc(DatastoreOptions datastoreOptions) throws IOException {
               ? getClientContextForEmulator(datastoreOptions)
               : getClientContext(datastoreOptions);
 
+      /* For grpc transport options, configure default gRPC Connection pool with minChannelCount = 1 and maxChannelCount = 4 */
       DatastoreStubSettings datastoreStubSettings =
           DatastoreStubSettings.newBuilder(clientContext)
               .applyToAllUnaryMethods(retrySettingSetter(datastoreOptions))
+              .setTransportChannelProvider(
+                  DatastoreSettings.defaultGrpcTransportProviderBuilder()
+                      .setChannelPoolSettings(
+                          ChannelPoolSettings.builder()
+                              .setInitialChannelCount(DatastoreOptions.INIT_CHANNEL_COUNT)
+                              .setMinChannelCount(DatastoreOptions.MIN_CHANNEL_COUNT)
+                              .setMaxChannelCount(DatastoreOptions.MAX_CHANNEL_COUNT)
+                              .build())
+                      .build())
               .build();
       datastoreStub = GrpcDatastoreStub.create(datastoreStubSettings);
     } catch (IOException e) {

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

@@ -103,6 +103,25 @@ public void testDatastore() {
     assertSame(datastoreRpc, options.build().getRpc());
   }
 
+  @Test
+  public void testGrpcDefaultChannelConfigurations() {
+    DatastoreOptions datastoreOptions =
+        DatastoreOptions.newBuilder()
+            .setServiceRpcFactory(datastoreRpcFactory)
+            .setProjectId(PROJECT_ID)
+            .setDatabaseId(DATABASE_ID)
+            .setTransportOptions(GrpcTransportOptions.newBuilder().build())
+            .setCredentials(NoCredentials.getInstance())
+            .setHost("http://localhost:" + PORT)
+            .build();
+    ChannelPoolSettings channelPoolSettings =
+        ((InstantiatingGrpcChannelProvider) datastoreOptions.getTransportChannelProvider())
+            .getChannelPoolSettings();
+    assertEquals(channelPoolSettings.getInitialChannelCount(), DatastoreOptions.INIT_CHANNEL_COUNT);
+    assertEquals(channelPoolSettings.getMinChannelCount(), DatastoreOptions.MIN_CHANNEL_COUNT);
+    assertEquals(channelPoolSettings.getMaxChannelCount(), DatastoreOptions.MAX_CHANNEL_COUNT);
+  }
+
   @Test
   public void testCustomChannelAndCredentials() {
     InstantiatingGrpcChannelProvider channelProvider =