protected void readAndUpdateNewBlock(long firstDataBlockOffset) throws IOException {
      HFileBlock newBlock = reader.readBlock(firstDataBlockOffset, -1, cacheBlocks, pread,
        isCompaction, true, BlockType.DATA, getEffectiveDataBlockEncoding());
      if (newBlock.getOffset() < 0) {
        releaseIfNotCurBlock(newBlock);
        throw new IOException(
          "Invalid offset=" + newBlock.getOffset() + ", path=" + reader.getPath());
      }
      updateCurrentBlock(newBlock);
    }
Positions this scanner at the start of the file.
@return false if empty file; i.e. a call to next would return false and the current key and
        value are undefined.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java