Dne 29 Říjen 2014, 12:31, Petr Jelinek napsal(a):
> On 29/10/14 10:41, David Rowley wrote:
>> On Mon, Oct 13, 2014 at 11:00 AM, Tomas Vondra <tv@fuzzy.cz
>>
>> The last point is really just "unfinished implementation" - the
>> syntax I
>> propose is this:
>>
>> ALTER TABLE ... ADD STATISTICS (options) ON (columns)
>>
>> where the options influence the MCV list and histogram size, etc.
>> The
>> options are recognized and may give you an idea of what it might do,
>> but
>> it's not really used at the moment (except for storing in the
>> pg_mv_statistic catalog).
>>
>>
>>
>> I've not really gotten around to looking at the patch yet, but I'm also
>> wondering if it would be simple include allowing functional statistics
>> too. The pg_mv_statistic name seems to indicate multi columns, but how
>> about stats on date(datetime_column), or perhaps any non-volatile
>> function. This would help to solve the problem highlighted here
>> http://www.postgresql.org/message-id/CAApHDvp2vH=7O-gp-zAf7aWy+A-WHWVg7h3Vc6=5pf9Uf34DhQ@mail.gmail.com
>> . Without giving it too much thought, perhaps any expression that can be
>> indexed should be allowed to have stats? Would that be really difficult
>> to implement in comparison to what you've already done with the patch so
>> far?
>>
>
> I would not over-complicate requirements for the first version of this,
> I think it's already complicated enough.
My thoughts, exactly. I'm not willing to put more features into the
initial version of the patch. Actually, I'm thinking about ripping out
some experimental features (particularly "hashed MCV" and "associative
rules").
> Quick look at the patch suggests that it mainly needs discussion about
> design and particular implementation choices, there is fair amount of
> TODOs and FIXMEs. I'd like to look at it too but I doubt that I'll have
> time to do in depth review in this CF.
Yes. I think it's a bit premature to discuss the code thoroughly at this
point - I'd like to discuss the general approach to the feature (i.e.
minimizing the impact on those not using it, etc.).
The most interesting part of the code are probably the comments,
explaining the design in more detail, known shortcomings and possible ways
to address them.
regards
Tomas