Re: proposal: searching in array function - array_position

2015-03-10 22:53 GMT+01:00 Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>:

> On 2/22/15 5:19 AM, Pavel Stehule wrote:
>
>>
>>
>> 2015-02-22 3:00 GMT+01:00 Petr Jelinek <petr(at)2ndquadrant(dot)com
>> <mailto:petr(at)2ndquadrant(dot)com>>:
>>
>> On 28/01/15 08:15, Pavel Stehule wrote:
>>
>>
>>
>> 2015-01-28 0:01 GMT+01:00 Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com
>> <mailto:Jim(dot)Nasby(at)bluetreble(dot)com>
>> <mailto:Jim(dot)Nasby(at)bluetreble(dot)__com
>> <mailto:Jim(dot)Nasby(at)bluetreble(dot)com>>>:
>>
>> On 1/27/15 4:36 AM, Pavel Stehule wrote:
>>
>>
>> It is only partially identical - I would to use cache for
>> array_offset, but it is not necessary for array_offsets
>> ..
>> depends how we would to modify current API to support
>> externally
>> cached data.
>>
>>
>> Externally cached data?
>>
>>
>> Some from these functions has own caches for minimize access to
>> typcache
>> (array_map, array_cmp is example). And in first case, I am trying
>> to
>> push these information from fn_extra, in second case I don't do
>> it,
>> because I don't expect a repeated call (and I am expecting so
>> type cache
>> will be enough).
>>
>>
>> You actually do caching via fn_extra in both case and I think that's
>> the correct way, and yes that part can be moved common function.
>>
>> I also see that the documentation does not say what is returned by
>> array_offset if nothing is found (it's documented in code but not in
>> sgml).
>>
>>
>> rebased + fixed docs
>>
>
> I don't think we need both array_offset and array_offset_start; can't both
> SQL functions just call one C function?
>

There is a rule about unique mapping C functions to SQL space - and I don't
think so this rule is bad.

>
> It might be worth combining the array and non-array versions of this, by
> having a _common function that accepts a boolean and then just run one or
> the other of the while loops. Most of the code seems to be shared between
> the two versions.
>
> What is this comment supposed to mean? There is no 'width_array'...
>

It is typo (I am sorry) - should be width_bucket(, array)

http://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=e80252d424278abf65b624669c8e6b3fe8587cac

The code is similar, but it expect large **sorted** input. array_offset
works on unsorted (alphabetical unsorted) data sets - like days of week ..

>
> * Biggest difference against width_array is unsorted input array.
>
> I've attached my doc changes, both alone and with the code.
>
> --
> Jim Nasby, Data Architect, Blue Treble Consulting
> Data in Trouble? Get it in Treble! http://BlueTreble.com
>