| From: | Taral <taral(at)taral(dot)net> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: No merge sort? |
| Date: | 2003-03-15 04:07:03 |
| Message-ID: | 20030315040703.GA3313@taral.net |
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| Lists: | pgsql-hackers |
On Fri, Mar 14, 2003 at 10:43:30PM -0500, Tom Lane wrote:
> Sure. That's why we have a planner that distinguishes between startup
> cost and total cost, and interpolates when a LIMIT is involved. But
> if this mergesort idea only helps for small-limit cases, that's another
> restriction on its scope of usefulness...
I don't think so, since even in the non-limit case it avoids having to
do a full sort if the number of initial streams is finite and small (as
in the case I demonstrated), reducing time complexity to O(N).
--
Taral <taral(at)taral(dot)net>
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