RandProcessId MUST be 64-bits and not 32-bits

Author: odeke-em

google-cloud-spanner/src/main/java/com/google/cloud/spanner/XGoogSpannerRequestId.java

@@ -47,7 +47,8 @@ public static XGoogSpannerRequestId of(
   }
 
   private static String generateRandProcessId() {
-    return String.format("%08x", new SecureRandom().nextInt());
+    // Expecting to use 64-bits of randomness to avoid clashes.
+    return String.format("%016x", new SecureRandom().nextInt(64));
   }
 
   @Override

google-cloud-spanner/src/test/java/com/google/cloud/spanner/XGoogSpannerRequestIdTest.java

@@ -29,7 +29,7 @@
 @RunWith(JUnit4.class)
 public class XGoogSpannerRequestIdTest {
   private static final Pattern REGEX_RAND_PROCESS_ID =
-      Pattern.compile("1.([0-9a-z]{8})(\\.\\d+){3}\\.(\\d+)$");
+      Pattern.compile("1.([0-9a-z]{16})(\\.\\d+){3}\\.(\\d+)$");
 
   @Test
   public void testEquals() {