Question

Explain why it is not good to do sorting in hard drive. List and explain the steps of blocked sort-based indexing

Answer 1

It is not good to do sorting in hard drive  as the external sort minimises the amount of data read and written to external storage (and historically also seek times), and a general-purpose virtual memory implementation on top of a sort algorithm not designed for this will not be competitive with an algorithm designed to minimise IO.

The steps of blocked based indexing are:

Block merge indexing:

1. Parse documents into (TermID, DocID) pairs until “block” is full

2 Invert the block

3. Sort the (TermID,DocID) pairs

4 Write the block to disk

5 Then merge all blocks into one large postings file

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