Re: TRUNCATE TABLE corrupts pg_class.relfilenode = pg_attrdef.pg_attrdef

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
>>
>>
>
>
>