| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Boszormenyi Zoltan <zb(at)cybertec(dot)at> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers Hackers <pgsql-hackers(at)postgresql(dot)org>, Josh Berkus <josh(at)agliodbs(dot)com> |
| Subject: | Re: plan time of MASSIVE partitioning ... |
| Date: | 2010-10-29 06:08:34 |
| Message-ID: | 24391.1288332514@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
I wrote:
> the right way to make this faster is to refactor things so that we
> don't generate useless equivalence classes in the first place, or
> at least don't keep them around in the planner's lists once we realize
> they're useless.
After a bit of hacking, I propose the attached patch.
> I like Heikki's hack to cut down on searching in make_canonical_pathkey,
> but I think that complicating the data structure searching beyond that
> is just a band-aid.
With the given test case and this patch, we end up with exactly two
canonical pathkeys referencing a single EquivalenceClass. So as far
as I can tell there's not a lot of point in refining the pathkey
searching. Now, the EquivalenceClass has got 483 members, which
means that there's still some O(N^2) behavior in
get_eclass_for_sort_expr. There might be some use in refining the
search for a matching eclass member. It's not sticking out in
profiling like it did before though.
regards, tom lane
| Attachment | Content-Type | Size |
|---|---|---|
| avoid-useless-eclasses.patch | text/x-patch | 27.6 KB |
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