Re: WIP: BRIN multi-range indexes

On 03/02/2018 05:08 AM, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
>> On 2018-02-25 01:30:47 +0100, Tomas Vondra wrote:
>>> Note: Currently, this only works with float8-based data types.
>>> Supporting additional data types is not a big issue, but will
>>> require extending the opclass with "subtract" operator (used to
>>> compute distance between values when merging ranges).
>
>> Based on Tom's past stances I'm a bit doubtful he'd be happy with such a
>> restriction. Note that something similar-ish also has come up in
>> 0a459cec96.
>

That restriction was lifted quite a long time ago, so now both index
types support pretty much the same data types as the original BRIN (with
the reltime/abstime exception, discussed in this thread earlier).

>> I kinda wonder if there's any way to not have two similar but not
>> equal types of logic here?
>
> Hm. I wonder what the patch intends to do with subtraction overflow,
> or infinities, or NaNs. Just as with the RANGE patch, it does not
> seem to me that failure is really an acceptable option. Indexes are
> supposed to be able to index whatever the column datatype can store.
>

I admit that's something I haven't thought about very much. I'll look
into that, of course, but the indexes are only using the deltas to pick
which ranges to merge, so I think in the worst case it may results in
sub-optimal index. But let me check what the RANGE patch did.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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