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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: PoC/WIP: Extended statistics on expressions
Date: Fri, 22 Jan 2021 14:06:51 +0100
Message-ID: <901b9cf3-78f3-9cc4-94a6-8ab4dfa5f34b@enterprisedb.com> (raw)
In-Reply-To: <CAEZATCVjxvLsn_kXKC+dgVo7OGBBNROGq4Ok5N1QAoMN7Bg8gQ@mail.gmail.com>
References: <20210116232208.GB8560@telsasoft.com>
	<2f2a3b3b-93e4-723f-144e-bc21f10d6b61@enterprisedb.com>
	<20210118045331.GF8560@telsasoft.com>
	<CAEZATCVnQccV_Z7AuvbvquaOYxUj+cVFk48pPGASYHFjXWgW5g@mail.gmail.com>
	<3f20da4d-89dc-0912-98d2-b6f0ef06c87f@enterprisedb.com>
	<CAEZATCUuj5FPjtOU2=7Z2pTC8LEvrf79+Go7R8yQ+eE0ezfgfQ@mail.gmail.com>
	<f865af90-c19c-769e-8c65-19692e245479@enterprisedb.com>
	<20210122022958.GC27167@telsasoft.com>
	<acf27932-8159-8872-8fca-902c7a35b351@enterprisedb.com>
	<20210122040101.GF27167@telsasoft.com>
	<20210122044606.GG27167@telsasoft.com>
	<CAEZATCVjxvLsn_kXKC+dgVo7OGBBNROGq4Ok5N1QAoMN7Bg8gQ@mail.gmail.com>



On 1/22/21 10:00 AM, Dean Rasheed wrote:
> On Fri, 22 Jan 2021 at 04:46, Justin Pryzby <pryzby@telsasoft.com> wrote:
>>
>> I think you'll maybe have to do something better - this seems a bit too weird:
>>
>> | postgres=# CREATE STATISTICS s2 ON (i+1) ,i FROM t;
>> | postgres=# \d t
>> | ...
>> |     "public"."s2" (ndistinct, dependencies, mcv) ON i FROM t
>>
> 
> I guess that's not surprising, given that old psql knows nothing about
> expressions in stats.
> 
> In general, I think connecting old versions of psql to newer servers
> is not supported. You're lucky if \d works at all. So it shouldn't be
> this patch's responsibility to make that output nicer.
> 

Yeah. It's not clear to me what exactly could we do with this, without 
"backpatching" the old psql or making the ruleutils.c consider version 
of the psql. Neither of these seems possible/acceptable.

I'm sure this is not the only place showing "incomplete" information in 
old psql on new server.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company





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