@Override
  public synchronized boolean reseek(byte[] row) throws IOException {
    return TraceUtil.trace(() -> {
      if (row == null) {
        throw new IllegalArgumentException("Row cannot be null.");
      }
      boolean result = false;
      region.startRegionOperation();
      ExtendedCell kv = PrivateCellUtil.createFirstOnRow(row, 0, (short) row.length);
      try {
        // use request seek to make use of the lazy seek option. See HBASE-5520
        result = this.storeHeap.requestSeek(kv, true, true);
        if (this.joinedHeap != null) {
          result = this.joinedHeap.requestSeek(kv, true, true) || result;
        }
      } finally {
        region.closeRegionOperation();
      }
      return result;
    }, () -> region.createRegionSpan("RegionScanner.reseek"));
  }
A mocked list implementation - discards all updates.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionScannerImpl.java