chore(spanner): enable dynamic channel pooling by default

Author: harshachinta

google-cloud-spanner/pom.xml

@@ -162,6 +162,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>grpc-gcp</artifactId>
+      <version>1.6.2-SNAPSHOT</version>
     </dependency>
     <dependency>
       <groupId>io.grpc</groupId>

google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java

@@ -60,6 +60,7 @@
 import com.google.cloud.grpc.GcpManagedChannel;
 import com.google.cloud.grpc.GcpManagedChannelBuilder;
 import com.google.cloud.grpc.GcpManagedChannelOptions;
+import com.google.cloud.grpc.GcpManagedChannelOptions.GcpChannelPoolOptions;
 import com.google.cloud.grpc.GcpManagedChannelOptions.GcpMetricsOptions;
 import com.google.cloud.grpc.GrpcTransportOptions;
 import com.google.cloud.spanner.AdminRequestsPerMinuteExceededException;
@@ -589,8 +590,11 @@ private static GcpManagedChannelOptions grpcGcpOptionsWithMetrics(SpannerOptions
     if (metricsOptions.getNamePrefix().equals("")) {
       metricsOptionsBuilder.withNamePrefix("cloud.google.com/java/spanner/gcp-channel-pool/");
     }
+    GcpChannelPoolOptions.Builder channelPoolOptionsBuilder =
+        GcpChannelPoolOptions.newBuilder().setDynamicScaling(0, 100, Duration.ofMinutes(30L));
     return GcpManagedChannelOptions.newBuilder(grpcGcpOptions)
         .withMetricsOptions(metricsOptionsBuilder.build())
+        .withChannelPoolOptions(channelPoolOptionsBuilder.build())
         .build();
   }