Date: Mon, 13 Jul 2020 02:14:19 +0200
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	Alexander Korotkov <a.korotkov@postgrespro.ru>,
	Michael Paquier <michael@paquier.xyz>, Tom Lane <tgl@sss.pgh.pa.us>,
	Andres Freund <andres@anarazel.de>,
	Mark Dilger <hornschnorter@gmail.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: WIP: BRIN multi-range indexes
Message-ID: <20200713001419.te5aozy7o76ff2vk@development>
References: <20200710120914.6kydpi3kfr2icpfq@development>
 <20200712235854.GA21540@alvherre.pgsql>
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On Sun, Jul 12, 2020 at 07:58:54PM -0400, Alvaro Herrera wrote:
>On 2020-Jul-10, Tomas Vondra wrote:
>
>> > postgres(1:12801)=# select * from brin_page_items(get_raw_page('mul',
>> > 2), 'mul');
>> > -[ RECORD 1 ]----------------------------------------------------------------------------------------------------------------------
>> > -----------------------------------------------------------------------------------------------------------------------------------
>> > ----------------------------
>> > itemoffset  | 1
>> > blknum      | 0
>> > attnum      | 1
>> > allnulls    | f
>> > hasnulls    | f
>> > placeholder | f
>> > value       | {\x010000001b0000002000000001000000e5700000e6700000e7700000e8700000e9700000ea700000eb700000ec700000ed700000ee700000ef
>> > 700000f0700000f1700000f2700000f3700000f4700000f5700000f6700000f7700000f8700000f9700000fa700000fb700000fc700000fd700000fe700000ff700
>> > 00000710000}
>>
>> Hmm. I'm not sure we can do much better, without making the function
>> much more complicated. I mean, even with regular BRIN indexes we don't
>> really know if the value is plain min/max, right?
>
>Maybe we can try to handle this with some other function that interprets
>the bytea in 'value' and returns a user-readable text.  I think it'd
>have to be a superuser-only function, because otherwise you could easily
>cause a crash by passing a value of a different opclass.  But since this
>seems a developer-only thing, that restriction seems fine to me.
>

Ummm, I disagree a superuser check is sufficient protection from a
segfault or similar issues. If we really want to print something nicer,
I'd say it needs to be a special function in the BRIN opclass.

>(I don't know what's a good way to represent a bloom filter, mind.)
>

Me neither, but I guess we could print either some stats (size, number
of bits set, etc.) and/or then the bitmap.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services