core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/statistic/OSessionStoragePerformanceStatistic.java
public void stopWALFlushTimer() {
    final long endTs = nanoTimer.getNano();
    final long timeDiff = (endTs - timeStamps.pop());

    if (walCountersHolder == null)
      walCountersHolder = new WALCountersHolder();

    walCountersHolder.flushCount++;
    walCountersHolder.flushTime += timeDiff;

    makeSnapshotIfNeeded(endTs);
  }
public void stopWALFlushTimer() {
    final long endTs = nanoTimer.getNano();
    final long timeDiff = (endTs - timeStamps.pop());

    if (walCountersHolder == null)
      walCountersHolder = new WALCountersHolder();

    walCountersHolder.flushCount++;
    walCountersHolder.flushTime += timeDiff;

    makeSnapshotIfNeeded(endTs);
  }
Stops timer and records how much time was spent on flushing of data from write ahead log cache.