@Override
  protected String progressInfo() {
    StringBuilder sb = new StringBuilder();
    appendToStatus(sb, "verified", numKeysVerified.get());
    appendToStatus(sb, "READ FAILURES", numReadFailures.get());
    appendToStatus(sb, "READ ERRORS", numReadErrors.get());
    appendToStatus(sb, "NULL RESULT", nullResult.get());
    return sb.toString();
  }
Should only be used for the concurrent writer/reader workload. The maximum key we are allowed
to read, subject to the "key window" constraint.
hbase-diagnostics/src/main/java/org/apache/hadoop/hbase/util/MultiThreadedReader.java