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Rows vs Columns (cont)

Storing sorted columns leads to
  • potential for effective compression
    • compression ⇒ more projections in same space
    • no need to compress all columns  (if some aren't "compressible")
  • sorted data is useful in some query evaluation contexts
    • e.g. terminating scan once unique match found
    • e.g. sort-merge join
Only one column in each projection will be sorted
  • but if even one projection has a column sorted how you need ...