core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/statistic/OSessionStoragePerformanceStatistic.java
public WALCountersHolder pushWALCounters(WALCountersHolder holder) {
    if (snapshot == null)
      return holder;

    if (snapshot.walCountersHolder == null)
      return holder;

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

    snapshot.walCountersHolder.pushData(holder);

    return holder;
  }
public WALCountersHolder pushWALCounters(WALCountersHolder holder) {
    if (snapshot == null)
      return holder;

    if (snapshot.walCountersHolder == null)
      return holder;

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

    snapshot.walCountersHolder.pushData(holder);

    return holder;
  }
Takes write ahead log data from last snapshot and aggregates them with data passed inside method as parameter. Result of
aggregation of performance data is returned inside of passed in performance data and as result of this method call.

@param holder Performance data for write ahead log may be <code>null</code>

@return Result of aggregation of performance data