From: | Andreas Karlsson <andreas(at)proxel(dot)se> |
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To: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: PoC: Partial sort |
Date: | 2013-12-14 19:47:23 |
Message-ID: | 52ACB5CB.2040608@proxel.se |
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Lists: | pgsql-hackers |
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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