On 12/14/2013 10:59 AM, Alexander Korotkov wrote:
This patch allows to use index for order-by if order-by clause and index
has non-empty common prefix. So, index gives right ordering for first n
order-by columns. In order to provide right order for rest m columns,
sort node is inserted. This sort node sorts groups of tuples where
values of first n order-by columns are equal.


I recently looked at the same problem. I see that you solved the rescanning problem by simply forcing the sort to be redone on ExecReScanSort if you have done a partial sort.

My idea for a solution was to modify tuplesort to allow storing the already sorted keys in either memtuples or the sort result file, but setting a field so it does not sort thee already sorted tuples again. This would allow the rescan to work as it used to, but I am unsure how clean or ugly this code would be. Was this something you considered?

--
Andreas Karlsson


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