Re: Indexam interface proposal

Added to TODO:

* Allow index scans to return matching index keys

http://archives.postgresql.org/pgsql-hackers/2007-03/msg01079.php

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Heikki Linnakangas wrote:
> Currently amgettuple returns one matching tuple at a time, in index
> order. I'm proposing two changes to add support for
> - candidate matches
> - partial ordering
>
> Those two features are essential to make clustered indexes work, and in
> the future, binned bitmap indexes that don't have a bitmap for each
> distinct value but for ranges of values.
>
> There's a third feature looming in the future, that I haven't addressed:
> - returning index values, for index-only scans or at least for filtering
> rows before fetching heap tuples.
>
>
> I'm proposing that we keep the one tuple per call nature of the
> interface, but add a flag to mark candidate matches. index_getnext or
> the executor would need to recheck the original quals for tuples marked
> as candidates.
>
> Another flag would be used to mean "this tuple marks the boundary of a
> partial ordering". Let's call it boundary_mark for now.
>
> For example, if an index scan returned tuples with the following keys,
> with tuples on same line meaning the index doesn't know their relative
> ordering.
>
> 1
> 3 4 2
> 5 8 6 7
> 9
> 10
>
> amgettuple would return the above tuples like this:
>
> 1 3 4 2 5 8 6 7 9 10
> * * * * *
>
> where the tuples marked with * would have the boundary_mark-flag set. If
> the plan requires ordered results, index_getnext would have to sort
> tuples between two markers before returning them to the caller.
>
> amgetmulti would also need to have the candidate-flag added as I
> proposed in the "Bitmapindexscan changes" patch I sent earlier to
> pgsql-patches.
>
> This interface change would solve much of the ugliness of my GIT patch,
> by generalizing the index quals checking and sorting code to index_getnext.
>
> Another source of ugliness in the patch is in inserting new tuples.
> Inserts need to reach to the heap to fetch heap tuples, to compare keys
> when splitting a group. I don't see a clean fix for that, but I don't
> think it's as bad as the index scan code.
>
> --
> Heikki Linnakangas
> EnterpriseDB http://www.enterprisedb.com
>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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