Subject: Re: WIP: BRIN multi-range indexes
To: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>
Cc: Mark Dilger <hornschnorter@gmail.com>,
 Alvaro Herrera <alvherre@alvh.no-ip.org>, pgsql-hackers@postgreSQL.org
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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <4d31b358-77d9-c2d7-e0eb-319bda6456ad@2ndquadrant.com>
Date: Fri, 2 Mar 2018 18:09:50 +0100
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On 03/02/2018 05:08 AM, Tom Lane wrote:
> Andres Freund <andres@anarazel.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
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services