Avoid retrieval of CHECK constraints and DEFAULT exprs in data-only dump

Those extra queries are not necessary when doing a data-only dump.  With
this change, this means that the dependencies between CHECK/DEFAULT and
the parent table are not tracked anymore for a data-only dump.  However,
these dependencies are only used for the schema generation and we have
never guaranteed that a dump can be reloaded if a CHECK constraint uses
a custom function whose behavior changes when loading the data, like
when using cross-table references in the CHECK function.

Author: Julien Rouhaud
Reviewed-by: Daniel Gustafsson, Michael Paquier
Discussion: https://postgr.es/m/20200712054850.GA92357@nol

Author: michaelpq

src/bin/pg_dump/pg_dump.c

@@ -8644,9 +8644,10 @@ getTableAttrs(Archive *fout, TableInfo *tblinfo, int numTables)
 		PQclear(res);
 
 		/*
-		 * Get info about column defaults
+		 * Get info about column defaults.  This is skipped for a data-only
+		 * dump, as it is only needed for table schemas.
 		 */
-		if (hasdefaults)
+		if (!dopt->dataOnly && hasdefaults)
 		{
 			AttrDefInfo *attrdefs;
 			int			numDefaults;
@@ -8731,9 +8732,10 @@ getTableAttrs(Archive *fout, TableInfo *tblinfo, int numTables)
 		}
 
 		/*
-		 * Get info about table CHECK constraints
+		 * Get info about table CHECK constraints.  This is skipped for a
+		 * data-only dump, as it is only needed for table schemas.
 		 */
-		if (tbinfo->ncheck > 0)
+		if (!dopt->dataOnly && tbinfo->ncheck > 0)
 		{
 			ConstraintInfo *constrs;
 			int			numConstrs;