Date: Thu, 10 Oct 2019 01:07:59 +0200
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: buschmann@nidsa.net, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16045: vacuum_db crash and illegal memory alloc after
 pg_upgrade from PG11 to PG12
Message-ID: <20191009230759.ge66neof5qj627a2@development>
References: <16045-673e8fa6b5ace196@postgresql.org>
 <20191009132436.uugh4r3be6vw6ex4@development>
 <20191009135907.km2b5nrzflcz6xey@development>
 <20191009141841.my6k44wfiaquj3ks@development>
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Well, I think I found the root cause. It's because of 7c15cef86d, which
changed the definition of sql_identifier so that it's a domain over name
instead of varchar. So we now have this:

  SELECT typname, typlen FROM pg_type WHERE typname = 'sql_identifier':

  -[ RECORD 1 ]--+---------------
  typname        | sql_identifier
  typlen         | -1

instead of this

  -[ RECORD 1 ]--+---------------
  typname        | sql_identifier
  typlen         | 64

Unfortunately, that seems very much like a break of on-disk format, and
after pg_upgrade any table containing sql_identifier columns is pretty
much guaranteed to be badly mangled. For example, the first row from the
table used in the original report looks like this on PostgreSQL 11:

  test=# select ctid, * from q_tbl_archiv limit 1;
  -[ RECORD 1 ]----+--------------------------
  ctid             | (0,1)
  table_name       | _pg_foreign_data_wrappers
  column_name      | foreign_data_wrapper_name
  ordinal_position | 5
  col_qualifier    | foreign_data_wrapper_name
  id_column        | 
  id_default       | 

while on PostgreSQL 12 after pg_upgrade it looks like this

  test=# select ctid, table_name, column_name, ordinal_position from q_tbl_archiv limit 1;:
  -[ RECORD 1 ]----+---------------------------------------------------------
  ctid             | (0,1)
  table_name       | 5_pg_foreign_data_wrappers5foreign_data_wrapper_name\x05
  column_name      | _data_wrapper_name
  ordinal_position | 0

Not sure what to do about this :-(


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services