private final void checkTagsLen() {
      if (checkLen(this.currTagsLen)) {
        throw new IllegalStateException(
          "Invalid currTagsLen " + this.currTagsLen + ". Block offset: " + curBlock.getOffset()
            + ", block length: " + this.blockBuffer.limit() + ", position: "
            + this.blockBuffer.position() + " (without header)." + " path=" + reader.getPath());
      }
    }
The next indexed key is to keep track of the indexed key of the next data block. If the
nextIndexedKey is HConstants.NO_NEXT_INDEXED_KEY, it means that the current data block is the
last data block. If the nextIndexedKey is null, it means the nextIndexedKey has not been
loaded yet.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java