private String formatMessage(long extraSleepTime, List<String> gcDiffs) {
    String ret = "Detected pause in JVM or host machine (eg GC): " + "pause of approximately "
      + extraSleepTime + "ms\n";
    if (gcDiffs.isEmpty()) {
      ret += "No GCs detected";
    } else {
      ret += Joiner.on("\n").join(gcDiffs);
    }
    return ret;
  }
log INFO if we detect a pause longer than this threshold
hbase-server/src/main/java/org/apache/hadoop/hbase/util/JvmPauseMonitor.java