[GitHub] [calcite] hqx871 commented on pull request #2363: [CALCITE-4522] Sort cost should account for the number of columns in collation

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hqx871 commented on pull request #2363:
URL: https://github.com/apache/calcite/pull/2363#issuecomment-799021206


   I made a little change as julianhyde suggested at https://issues.apache.org/jira/browse/CALCITE-4522
   - If fetch is zero, cpu cost is zero; otherwise,
   
   - if there are no sort keys, cost is min(fetch + offset, inputRowCount) * bytesPerRow; otherwise
   
   - cost is inputRowCount * log(min(fetch + offset, inputRowCount)) * bytesPerRow.
   
   a method Util.nLogM(n, m) would be useful, where n is the number of input rows, and m is the number of active rows (and therefore determines the number of times each row is compared and/or moved). We would call it as follows: Util.nLogM(inputRowCount, fetch + offset)). It would make sure that m is at least e (and therefore log is at least 1), and make sure that m is no greater than n.


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