Re: GSoC proposal. Index-only scans for GIST

2014-03-18 18:47 GMT+04:00 Robert Haas <robertmhaas(at)gmail(dot)com>
>
>
> > If the fetch() is specified by the developer, then using it, algorithm
> can
> > retrieve the data directly to output areas at this stage, without
> reference
> > to the heap.
>
> This seems to be the crux of your proposal, but it seems vague: what
> exactly do you mean by "retrieve the data directly to output areas"?
> What data are you going to retrieve and where are you going to put it?
>

I meant Datum that storages in Gist-tree nodes. Now gistgettuple() returns
xs_ctup.t_self (item pointer). I'm going to add index-only scan
functionality: gistsettuple() will return pointer and Datum itself as
xs_itup . So queue will contain both the pointer and the Datum. If
visibilitymap_test returns true then Datum from xs_itup would be added into
queue. Otherwise page must be scanned.

Another question to consider is: which operator classes do you
> anticipate that this will work for and which ones do you anticipate
> that it will not work for? Any operator class that lossifies that
> input data before storing it in the index is presumably doomed, but
> which ones do that, and which do not?
>

about amcanreturn:
I'm going to create function gistcanreturn() = If fetch() is defined for
all indexed columns?

And last point of my project is to implement fetch() for existing opclasses
based on GIST.

--
Best regards,
Lubennikova Anastasia