chore: Address code comments

Author: lqiu96

samples/snippets/src/main/java/com/example/bigquerystorage/ExportOpenTelemetry.java

@@ -175,7 +175,7 @@ private JsonStreamWriter createStreamWriter(String tableName)
       // For more information about JsonStreamWriter, see:
       // https://googleapis.dev/java/google-cloud-bigquerystorage/latest/com/google/cloud/bigquery/storage/v1/JsonStreamWriter.html
       return JsonStreamWriter.newBuilder(tableName, client)
-          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(100)))
+          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(10)))
           .setChannelProvider(
               BigQueryWriteSettings.defaultGrpcTransportProviderBuilder()
                   .setKeepAliveTime(org.threeten.bp.Duration.ofMinutes(1))

samples/snippets/src/main/java/com/example/bigquerystorage/ReadTimestampArrow.java

@@ -118,7 +118,7 @@ public static void main(String... args) throws Exception {
     try (BigQueryReadClient client = BigQueryReadClient.create()) {
       String parent = String.format("projects/%s", projectId);
 
-      // This example uses baby name data from the public datasets.
+      // This example uses citibike data from the public datasets.
       String srcTable =
           String.format(
               "projects/%s/datasets/%s/tables/%s",

samples/snippets/src/main/java/com/example/bigquerystorage/ReadTimestampAvro.java

@@ -85,7 +85,7 @@ public static void main(String... args) throws Exception {
     try (BigQueryReadClient client = BigQueryReadClient.create()) {
       String parent = String.format("projects/%s", projectId);
 
-      // This example uses baby name data from the public datasets.
+      // This example uses citibike data from the public datasets.
       String srcTable =
           String.format(
               "projects/%s/datasets/%s/tables/%s",

samples/snippets/src/main/java/com/example/bigquerystorage/WriteToDefaultStream.java

@@ -176,7 +176,7 @@ private JsonStreamWriter createStreamWriter(String tableName)
       // For more information about JsonStreamWriter, see:
       // https://googleapis.dev/java/google-cloud-bigquerystorage/latest/com/google/cloud/bigquery/storage/v1/JsonStreamWriter.html
       return JsonStreamWriter.newBuilder(tableName, client)
-          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(100)))
+          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(10)))
           .setChannelProvider(
               BigQueryWriteSettings.defaultGrpcTransportProviderBuilder()
                   .setKeepAliveTime(org.threeten.bp.Duration.ofMinutes(1))

samples/snippets/src/main/java/com/example/bigquerystorage/WriteToDefaultStreamTimestampJson.java

@@ -157,7 +157,7 @@ private JsonStreamWriter createStreamWriter(String tableName)
       // For more information about JsonStreamWriter, see:
       // https://googleapis.dev/java/google-cloud-bigquerystorage/latest/com/google/cloud/bigquery/storage/v1/JsonStreamWriter.html
       return JsonStreamWriter.newBuilder(tableName, client)
-          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(100)))
+          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(10)))
           .setChannelProvider(
               BigQueryWriteSettings.defaultGrpcTransportProviderBuilder()
                   .setKeepAliveTime(org.threeten.bp.Duration.ofMinutes(1))

samples/snippets/src/main/java/com/example/bigquerystorage/WriteToDefaultStreamTimestampWithArrow.java

@@ -71,6 +71,8 @@
  */
 public class WriteToDefaultStreamTimestampWithArrow {
 
+  public static final long NANOS = 1000000000L;
+
   public static void main(String[] args) throws InterruptedException, IOException {
     if (args.length < 3) {
       System.out.println(
@@ -100,8 +102,9 @@ private static ArrowRecordBatch buildRecordBatch(VectorSchemaRoot root, int rowC
     TimeStampNanoTZVector timestampField = (TimeStampNanoTZVector) root.getVector("timestampField");
     timestampField.allocateNew(rowCount);
 
+    Instant now = Instant.now();
     for (int i = 0; i < rowCount; i++) {
-      timestampField.set(i, Instant.now().getNano());
+      timestampField.set(i, now.getEpochSecond() * NANOS + now.getNano());
     }
     root.setRowCount(rowCount);
 
@@ -228,7 +231,7 @@ private StreamWriter createStreamWriter(String streamName, Schema arrowSchema)
       // For more information about StreamWriter, see:
       // https://cloud.google.com/java/docs/reference/google-cloud-bigquerystorage/latest/com.google.cloud.bigquery.storage.v1.StreamWriter
       return StreamWriter.newBuilder(streamName, client)
-          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(100)))
+          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(10)))
           .setChannelProvider(
               BigQueryWriteSettings.defaultGrpcTransportProviderBuilder()
                   .setKeepAliveTime(org.threeten.bp.Duration.ofMinutes(1))

samples/snippets/src/main/java/com/example/bigquerystorage/WriteToDefaultStreamWithArrow.java

@@ -236,7 +236,7 @@ private StreamWriter createStreamWriter(String streamName, Schema arrowSchema)
       // For more information about StreamWriter, see:
       // https://cloud.google.com/java/docs/reference/google-cloud-bigquerystorage/latest/com.google.cloud.bigquery.storage.v1.StreamWriter
       return StreamWriter.newBuilder(streamName, client)
-          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(100)))
+          .setExecutorProvider(FixedExecutorProvider.create(Executors.newScheduledThreadPool(10)))
           .setChannelProvider(
               BigQueryWriteSettings.defaultGrpcTransportProviderBuilder()
                   .setKeepAliveTime(org.threeten.bp.Duration.ofMinutes(1))