I sent already an email about this topic to pgsql-admins but I think that it might be more relevant to this mailing list. I'm trying to investigate a corruption that happened on a machine of one of our clients.
-I was asked to understand why the corruption happened and how can we fix it. I copied the data dir to my machine on my local pc and started investigate it. They realized that there is a problem when they tried to backup the database via pg_dump. The error they got :
pg_dump: query returned 2 rows instead of one: SELECT tableoid, oid, (SELECT rolname FROM pg_catalog.pg_roles WHERE oid = datdba) AS dba, pg_encoding_to_char(encoding) AS encoding, datcollate, datctype, datfrozenxid, (SELECT spcname FROM pg_tablespace t WHERE t.oid = dattablespace) AS tablespace, shobj_description(oid, 'pg_database') AS description FROM pg_database WHERE datname = 'db1'
So I checked and indeed there were duplicated rows in the pg_roles / pg_database tables. Moreover, there were multiple values in all the system catalogs !
The first think I did as Tom Lane suggested is to upgrade to v9.2.24. Afterwards I vacuumed all the databases but nothing helped. I tried to reindex the databases but I got the next error :
2018-08-28 21:50:03 +08 db2 24360 ERROR: could not access status of transaction 32212695
2018-08-28 21:50:03 +08 db2 24360 DETAIL: Could not open file "pg_subtrans/01EB": No such file or directory.
So I tried to analyze all the system catalogs manualy one by one :
select 'VACUUM ANALYZE pg_catalog.'||table_name from information_schema.tables where table_schema = 'pg_catalog' and table_type <> 'VIEW';
?column?
---------------------------------------------------
VACUUM ANALYZE pg_catalog.pg_statistic
VACUUM ANALYZE pg_catalog.pg_type
VACUUM ANALYZE pg_catalog.pg_authid
VACUUM ANALYZE pg_catalog.pg_proc
VACUUM ANALYZE pg_catalog.pg_class
VACUUM ANALYZE pg_catalog.pg_user_mapping
.....
and I got error only on the next system table :
afa=# ANALYZE pg_catalog.pg_shdepend;
ERROR: could not access status of transaction 32212695
DETAIL: Could not open file "pg_subtrans/01EB": No such file or directory.
When I try to reindex the table I'm getting the same error.
Solutions I tried :
-vacuum all the databases
-reindex system db_name - > raise the same error (could not access status...)
-upgrade to v9.2.24 (still got corruption).
-Use zero_damaged_pages=0
-generate an empty subtransaction file with dd
-Trying to reindex system indexes in single mode -> raise same error.
*Tried to delete the duplicated values in some of the system tables by the ctid value, but nothing is deleted.
Any idea how can I continue ?
