Re: How to implement a SP-GiST index as a extension module?

On Mon, Oct 30, 2017 at 12:05 PM, Oleg Bartunov <obartunov(at)gmail(dot)com> wrote:
> On Sun, Oct 29, 2017 at 10:07 AM, Connor Wolf
> <wolf(at)imaginaryindustries(dot)com> wrote:
>> Hi there!
>>
>> I'm looking at implementing a custom indexing scheme, and I've been having
>> trouble understanding the proper approach.
>>
>> Basically, I need a BK tree, which is a tree-structure useful for indexing
>> arbitrary discrete metric-spaces (in my case, I'm interested in indexing
>> across the hamming edit-distance of perceptual hashes, for fuzzy image
>> searching). I'm pretty sure a SP-GiST index is the correct index type, as my
>> tree is intrinsically unbalanced.
>>
>> I have a functional stand-alone implementation of a BK-Tree, and it works
>> very well, but the complexity of managing what is basically a external index
>> for my database has reached the point where it's significantly problematic,
>> and it seems to be it should be moved into the database.
>>
>> Anyways, looking at the contents of postgres/src/backend/access/spgist, it
>> looks pretty straightforward in terms of the actual C implementation, but
>> I'm stuck understanding how to "install" a custom SP-GiST implementation.
>> There are several GiST indexing implementations in the contrib directory,
>> but no examples for how I'd go about implementing a loadable SP-GiST index.
>>
>> Basically, my questions are:
>>
>> Is it possible to implement a SP-GiST indexing scheme as a loadable module?
>>
>> If so, how?
>> And is there an example I can base my implementation off of?
>
> Look on RUM access method ( https://github.com/postgrespro/rum ) we
> developed using
> api available since 9.6.

or even simple, there is contrib/bloom access method, which illustrates
developing access method as an extension.

>
>
>>
>> I'm relatively comfortable with C (much moreso with C++), but I haven't
>> spent a lot of time looking at the postgresql codebase. I don't think I
>> could start from a empty folder and make a properly-implemented module in
>> any reasonable period of time, so if I have a working example for some sort
>> of index that uses the same interfaces that would really help a lot.
>>
>> Thanks!
>> Connor