Subject: Re: PoC/WIP: Extended statistics on expressions
To: Dean Rasheed <dean.a.rasheed@gmail.com>,
 Justin Pryzby <pryzby@telsasoft.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
Message-ID: <901b9cf3-78f3-9cc4-94a6-8ab4dfa5f34b@enterprisedb.com>
Date: Fri, 22 Jan 2021 14:06:51 +0100
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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