Subject: Re: TRUNCATE TABLE corrupts pg_class.relfilenode =
 pg_attrdef.pg_attrdef
To: pgsql-sql@postgresql.org
References: <66def74b-633e-65a0-cf44-4d486f15ebd9@4js.com>
 <291ca3cf-79af-c161-4213-182c35e43fe6@4js.com>
From: Sebastien FLAESCH <sf@4js.com>
Organization: Four Js Development Tools
Message-ID: <89f3d1ce-f11f-dfab-c780-50fa3d5836e9@4js.com>
Date: Mon, 22 May 2017 13:14:05 +0200
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Obviously pg_class.relfilenode can change when truncating tables:

test1=> select relfilenode from pg_class where relname = 'mytab';
  relfilenode
-------------
      6904188
(1 row)


test1=> truncate table mytab;


TRUNCATE TABLE
test1=> select relfilenode from pg_class where relname = 'mytab';
  relfilenode
-------------
      6904189
(1 row)


Seb

On 05/22/2017 01:07 PM, Sebastien FLAESCH wrote:
> Seems that the correct join condition should be:
>
>     (pg_class.oid = pg_attrdef.adrelid)
>
> I don't know why we have used pg_class.relfilenode...
>
> So this should be the correct SELECT statement:
>
> test1=> select a.adsrc from pg_class p join pg_attrdef a on (p.oid = a.adrelid) where lower(p.relname) = lower('mytab');
>                 adsrc
> -------------------------------------
>  nextval('mytab_pkey_seq'::regclass)
> (1 row)
>
>
> Can someone confirm?
>
> Thanks!
> Seb
>
>
> On 05/22/2017 12:51 PM, Sebastien FLAESCH wrote:
>> Hi all,
>>
>> Testing with Postgresql 9.6rc1 (but also detected with prior versions):
>>
>> It is normal that a TRUNCATE TABLE statement changes the table/sequence relation in pg_attrdef?
>>
>> test1=> create table mytab ( pkey serial, name varchar(10) );
>> test1=> select a.adsrc from pg_class p join pg_attrdef a on (p.relfilenode = a.adrelid) where lower(p.relname) = lower('mytab');
>>                 adsrc
>> -------------------------------------
>>  nextval('mytab_pkey_seq'::regclass)
>> (1 row)
>>
>> test1=> truncate table mytab;
>> TRUNCATE TABLE
>> test1=> select a.adsrc from pg_class p join pg_attrdef a on (p.relfilenode = a.adrelid) where lower(p.relname) = lower('mytab');
>>  adsrc
>> -------
>> (0 rows)
>>
>> test1=> select adrelid, adsrc from pg_attrdef where adsrc like '%mytab%';
>>  adrelid |                adsrc
>> ---------+-------------------------------------
>>  6904163 | nextval('mytab_pkey_seq'::regclass)
>> (1 row)
>>
>>
>> Are we mis-using the condition (p.relfilenode = a.adrelid) in the first SELECT?
>>
>> How can we easily check if a table is defined with a SERIAL type?
>>
>> Thanks!
>> Seb
>>
>>
>
>
>


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