| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Jim Nasby <jim(dot)nasby(at)openscg(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: [HACKERS] Re: Improve OR conditions on joined columns (common star schema problem) |
| Date: | 2018-02-03 00:50:35 |
| Message-ID: | 62132903-20a9-2e2a-13ed-d91da32cfb8f@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On 02/02/2018 03:26 PM, Tom Lane wrote:
> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
>> ISTM this patch got somewhat stuck as we're not quite sure the
>> transformation is correct in all cases. Is my impression correct?
>
> Yeah, that's the core issue.
>
>> If yes, how to we convince ourselves? Would some sort of automated testing
>> (generating data and queries) help? I'm willing to spend some cycles on
>> that, if considered helpful.
>
> I'm not sure if that would be enough to convince doubters. On the other
> hand, if it found problems, that would definitely be useful.
>
OK, I'll take a stab at this, then. I wasn't really suggesting it might
prove definitely prove the transformation is correct - clearly, it can
only find counter-examples. But I think it's worth it anyway.
BTW wouldn't it be possible to derive "traditional" proof in relational
algebra, similarly to other transforms?
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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