Re: vacuumlo

That can be verified by checking RELFILENODE of the table. VACUUM FULL
changes RELFILENODE:

|mgogala=# select relfilenode from pg_class where relname='emp';
 relfilenode
-------------
       52178
(1 row)

mgogala=# vacuum full emp;
VACUUM
mgogala=# select relfilenode from pg_class where relname='emp';
 relfilenode
-------------
       52182
(1 row)

|

According to unsubstantiated rumors from
https://www.postgresql.org/docs/13/catalog-pg-class.html, the definition
of RELFILENODE column is as follows:

relfilenode oid

Name of the on-disk file of this relation; zero means this is a “mapped”
relation whose disk file name is determined by low-level state

||Change of the RELFILENODE means that the relation has got a new file.
And that means that vacuum full rewrites the table, just as Laurenz has
said. Note that OID itself is NOT changed.
||

On 8/30/21 1:15 PM, Laurenz Albe wrote:
> VACUUM (FULL) will write a compact copy of the table, then delete the old one,
> so it temporarily needs more space. It may be a good idea to put "pg_wal" into
> a different file system, so that WAL space cannot run out even if the data files
> fill the file system. Then PostgreSQL won't crash, and the files will be removed.

--
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com