public long getFilenum() {
    return this.filenum.get();
  }
The class name of the runtime implementation, used as prefix for logging/tracing.
<p>
Performance testing shows getClass().getSimpleName() might be a bottleneck so we store it here,
refer to HBASE-17676 for more details
</p>
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java