pgsql: Don't access catalogs to validate GUCs when not connected to a D
Don't access catalogs to validate GUCs when not connected to a DB.
Vignesh found this bug in the check function for
default_table_access_method's check hook, but that was just copied
from older GUCs. Investigation by Michael and me then found the bug in
When not connected to a database (e.g. in a walsender connection), we
cannot perform (most) GUC checks that need database access. Even when
only shared tables are needed, unless they're
nailed (c.f. RelationCacheInitializePhase2()), they cannot be accessed
without pg_class etc. being present.
Fix by extending the existing IsTransactionState() checks to also
check for MyDatabaseOid.