Re: Surjective functional indexes

On 1 September 2017 at 09:47, Konstantin Knizhnik
<k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
>
> On 01.09.2017 09:25, Simon Riggs wrote:
>>
>> On 1 September 2017 at 05:40, Thomas Munro
>> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>>>
>>> On Fri, Jun 9, 2017 at 8:08 PM, Konstantin Knizhnik
>>> <k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
>>>>
>>>> Attached please find rebased version of the patch.
>>>> Now "projection" attribute is used instead of surjective/injective.
>>>
>>> Hi Konstantin,
>>>
>>> This still applies but it doesn't compile after commits 2cd70845 and
>>> c6293249. You need to change this:
>>>
>>> Form_pg_attribute att = RelationGetDescr(indexDesc)->attrs[i];
>>>
>>> ... to this:
>>>
>>> Form_pg_attribute att = TupleDescAttr(RelationGetDescr(indexDesc),
>>> i);
>>>
>>> Thanks!
>>
>> Does the patch work fully with that change? If so, I will review.
>>
> Attached please find rebased version of the patch.
> Yes, I checked that it works after this fix.
> Thank you in advance for review.

Thanks for the patch. Overall looks sound and I consider that we are
working towards commit for this.

The idea is that we default "projection = on", and can turn it off in
case the test is expensive. Why bother to have the option? (No docs at
all then!) Why not just evaluate the test and autotune whether to make
the test again in the future? That way we can avoid having an option
completely. I am imagining collecting values on the relcache entry for
the index.

To implement autotuning we would need to instrument the execution. We
could then display the collected value via EXPLAIN, so we could just
then use EXPLAIN in your tests rather than implementing a special
debug mode just for testing. We could also pass that information thru
to stats as well.

--
Simon Riggs http://www.2ndQuadrant.com/
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