Row and Page Count Influence on Estimated CPU, I/O Cost and Sort Memory Grants

From http://www.sqlskills.com/blogs/joe/exploring-row-and-page-count-impact-on-estimated-cpu-and-io-cost/

  • I/O Cost of a Clustered Index Scan is sensitive to page counts, but not row counts.
  • CPU Cost of a Clustered Index Scan is sensitive to row counts, but not data page counts

This can have effect on execution plan quality as well.

http://www.sqlskills.com/blogs/joe/data-page-count-influence-on-the-query-execution-plan/

From http://www.sqlskills.com/blogs/joe/row-and-page-count-influence-on-memory-grants/

  • The memory grant introduced by the Sort operator was sensitive to row counts, but not page counts.
  • The Sort operator’s estimated CPU and I/O costs were both sensitive to row counts, but not page counts.
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