Adds tracing sample for cloud spanner (#1002)

* Add tracing

* Fixes

* tracing

* Add tracing sample

* Revert Quickstart

* Revert Spanner sample

* Address review comments

* Fix style violations

spanner/cloud-client/README.md

@@ -34,5 +34,11 @@ You can then run a given `ClassName` via:
 ### Running the tutorial
     mvn exec:java -Dexec.mainClass=com.example.spanner.SpannerSample -Dexec.args="<command> my-instance my-database"
 
+## Tracing sample
+TracingSample.java demonstrates how to export traces generated by client library to StackDriver and to /tracez page.
+
+### Running the tracing sample
+    mvn exec:java -Dexec.mainClass=com.example.spanner.TracingSample -Dexec.args="my-instance my-database"
+
 ## Test
     mvn verify -Dspanner.test.instance=<instance id> -Dspanner.sample.database=<new database id>  -Dspanner.quickstart.database=<existing database id>

spanner/cloud-client/pom.xml

@@ -33,6 +33,7 @@ limitations under the License.
     <maven.compiler.target>1.8</maven.compiler.target>
     <maven.compiler.source>1.8</maven.compiler.source>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <opencensus.version>0.11.0</opencensus.version>
   </properties>
 
   <dependencies>
@@ -41,10 +42,14 @@ limitations under the License.
       <artifactId>google-cloud-spanner</artifactId>
       <version>0.33.0-beta</version>
       <exclusions>
-        <exclusion> <!-- exclude an old version of Guava -->
+        <exclusion>
           <groupId>com.google.guava</groupId>
           <artifactId>guava-jdk5</artifactId>
         </exclusion>
+        <exclusion>
+          <groupId>io.opencensus</groupId>
+          <artifactId>opencensus-api</artifactId>
+        </exclusion>
       </exclusions>
     </dependency>
 
@@ -53,6 +58,37 @@ limitations under the License.
       <artifactId>guava</artifactId>
       <version>20.0</version>
     </dependency>
+    <dependency>
+        <groupId>io.opencensus</groupId>
+        <artifactId>opencensus-api</artifactId>
+        <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>io.opencensus</groupId>
+        <artifactId>opencensus-impl</artifactId>
+        <version>${opencensus.version}</version>
+        <scope>runtime</scope>
+    </dependency>
+    <dependency>
+        <groupId>io.opencensus</groupId>
+        <artifactId>opencensus-contrib-zpages</artifactId>
+        <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>io.opencensus</groupId>
+        <artifactId>opencensus-exporter-trace-stackdriver</artifactId>
+        <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>io.opencensus</groupId>
+        <artifactId>opencensus-exporter-stats-stackdriver</artifactId>
+        <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>io.opencensus</groupId>
+        <artifactId>opencensus-contrib-grpc-metrics</artifactId>
+        <version>${opencensus.version}</version>
+    </dependency>
 
     <!-- Test dependencies -->
     <dependency>

spanner/cloud-client/src/main/java/com/example/spanner/TracingSample.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.spanner;
+
+import com.google.cloud.spanner.DatabaseClient;
+import com.google.cloud.spanner.DatabaseId;
+import com.google.cloud.spanner.ResultSet;
+import com.google.cloud.spanner.Spanner;
+import com.google.cloud.spanner.SpannerOptions;
+import com.google.cloud.spanner.Statement;
+
+import io.opencensus.common.Scope;
+import io.opencensus.contrib.grpc.metrics.RpcViews;
+import io.opencensus.contrib.zpages.ZPageHandlers;
+import io.opencensus.exporter.stats.stackdriver.StackdriverStatsExporter;
+import io.opencensus.exporter.trace.stackdriver.StackdriverExporter;
+import io.opencensus.trace.Tracing;
+import io.opencensus.trace.samplers.Samplers;
+
+import java.util.Arrays;
+
+/**
+ * This sample demonstrates how to enable opencensus tracing and stats in cloud spanner client.
+ */
+public class TracingSample {
+
+  private static final String SAMPLE_SPAN = "CloudSpannerSample";
+
+  public static void main(String[] args) throws Exception {
+    if (args.length != 2) {
+      System.err.println("Usage: TracingSample <instance_id> <database_id>");
+      return;
+    }
+    SpannerOptions options = SpannerOptions.newBuilder().build();
+    Spanner spanner = options.getService();
+
+    // Installs a handler for /tracez page.
+    ZPageHandlers.startHttpServerAndRegisterAll(8080);
+    // Installs an exporter for stack driver traces.
+    StackdriverExporter.createAndRegister();
+    Tracing.getExportComponent().getSampledSpanStore().registerSpanNamesForCollection(
+        Arrays.asList(SAMPLE_SPAN));
+
+    // Installs an exporter for stack driver stats.
+    StackdriverStatsExporter.createAndRegister();
+    RpcViews.registerAllCumulativeViews();
+
+    // Name of your instance & database.
+    String instanceId = args[0];
+    String databaseId = args[1];
+    try {
+      // Creates a database client
+      DatabaseClient dbClient = spanner.getDatabaseClient(DatabaseId.of(
+          options.getProjectId(), instanceId, databaseId));
+      // Queries the database
+      try (Scope ss = Tracing.getTracer()
+          .spanBuilderWithExplicitParent(SAMPLE_SPAN, null)
+          .setSampler(Samplers.alwaysSample())
+          .startScopedSpan()) {
+        ResultSet resultSet = dbClient.singleUse().executeQuery(Statement.of("SELECT 1"));
+
+        System.out.println("\n\nResults:");
+        // Prints the results
+        while (resultSet.next()) {
+          System.out.printf("%d\n\n", resultSet.getLong(0));
+        }
+      }
+    } finally {
+      // Closes the client which will free up the resources used
+      spanner.close();
+    }
+  }
+
+}