code: @Override
      public void recordTruncationMarker(long operationSequenceNumber, LogAddress address) {
          Exceptions.checkArgument(operationSequenceNumber >= 0, "operationSequenceNumber",
                  "Operation Sequence Number must be a positive number.");
          Preconditions.checkNotNull(address, "address");
          synchronized (this.truncationMarkers) {
              LogAddress existing = this.truncationMarkers.getOrDefault(operationSequenceNumber, null);
              if (existing == null || existing.getSequence() < address.getSequence()) {
                  this.truncationMarkers.put(operationSequenceNumber, address);
              }
          }
      }
docs: region TruncationMarkerRepository Implementation