Re: pg_upgrade and relkind filtering - Mailing list pgsql-hackers

On Mon, Dec 05, 2011 at 05:06:37PM -0500, Bruce Momjian wrote:
> Pg_upgrade has the following check to make sure the cluster is safe for
> upgrading:
> 
>         res = executeQueryOrDie(conn,
>                                 "SELECT n.nspname, c.relname, a.attname
> "
>                                 "FROM   pg_catalog.pg_class c, "
>                                 "       pg_catalog.pg_namespace n, "
>                                 "       pg_catalog.pg_attribute a "
>                                 "WHERE  c.oid = a.attrelid AND "
>                                 "       NOT a.attisdropped AND "
>                                 "       a.atttypid IN ( "
>           "         'pg_catalog.regproc'::pg_catalog.regtype, "
>           "         'pg_catalog.regprocedure'::pg_catalog.regtype, "
>           "         'pg_catalog.regoper'::pg_catalog.regtype, "
>           "         'pg_catalog.regoperator'::pg_catalog.regtype, "
>         /* regclass.oid is preserved, so 'regclass' is OK */
>         /* regtype.oid is preserved, so 'regtype' is OK */
>           "         'pg_catalog.regconfig'::pg_catalog.regtype, "
>           "         'pg_catalog.regdictionary'::pg_catalog.regtype) AND
> "
>           "     c.relnamespace = n.oid AND "
>           "     n.nspname != 'pg_catalog' AND "
>           "     n.nspname != 'information_schema'");
> 
> Based on a report from EnterpriseDB, I noticed that we check all
> pg_class entries, while there are cases where this is unnecessary
> because there is no data behind the entry, e.g. views.  Here are the
> relkinds supported:
> 
>     #define       RELKIND_RELATION        'r'       /* ordinary table */
>     #define       RELKIND_INDEX           'i'       /* secondary index */
>     #define       RELKIND_SEQUENCE        'S'       /* sequence object */
>     #define       RELKIND_TOASTVALUE      't'       /* for out-of-line values */
>     #define       RELKIND_VIEW            'v'       /* view */
>     #define       RELKIND_COMPOSITE_TYPE  'c'       /* composite type */
>     #define       RELKIND_FOREIGN_TABLE   'f'       /* foreign table */
>     #define       RELKIND_UNCATALOGED     'u'       /* not yet cataloged */
> 
> What types, other than views, can we skip in this query?

RELKIND_UNCATALOGED should never appear on disk, and RELKIND_SEQUENCE and
RELKIND_TOASTVALUE do not allow adding columns or changing column types.  We
might as well keep validating them.  RELKIND_RELATION and RELKIND_INDEX have
storage, so we must check those.

The remaining three relkinds (RELKIND_VIEW, RELKIND_COMPOSITE_TYPE,
RELKIND_FOREIGN_TABLE) have no storage, but all are usable as column types in
other relations that do have storage.  You could skip them iff they're unused
that way, per a check like find_composite_type_dependencies().