Re: PoC: Partial sort

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