Fast default stuff versus pg_upgrade

AFAICS, the fast-default patch neglected to consider what happens if
a database containing columns with active attmissingval entries is
pg_upgraded.  I do not see any code in either pg_dump or pg_upgrade that
attempts to deal with that situation, which means the effect will be
that the "missing" values will silently revert to nulls: they're still
null in the table storage, and the restored pg_attribute entries won't
have anything saying it should be different.

The pg_upgrade regression test fails to exercise such a case.  There is
only one table in the ending state of the regression database that has
any atthasmissing columns, and it's empty :-(.  If I add a table in
which there actually are active attmissingval entries, say according
to the attached patch, I get a failure in the pg_upgrade test.

This is certainly a stop-ship issue, and in fact it's bad enough
that I think we may need to pull the feature for v11.  Designing
binary-upgrade support for this seems like a rather large task
to be starting post-beta1.  Nor do I think it's okay to wait for
v12 to make it work; what if we have to force an initdb later in
beta, or recommend use of pg_upgrade for some manual catalog fix
after release?

            regards, tom lane

diff --git a/src/test/regress/expected/fast_default.out b/src/test/regress/expected/fast_default.out
index ef8d04f..f3d783c 100644
*** a/src/test/regress/expected/fast_default.out
--- b/src/test/regress/expected/fast_default.out
*************** DROP TABLE has_volatile;
*** 548,550 ****
--- 548,561 ----
  DROP EVENT TRIGGER has_volatile_rewrite;
  DROP FUNCTION log_rewrite;
  DROP SCHEMA fast_default;
+ -- Leave a table with an active fast default in place, for pg_upgrade testing
+ set search_path = public;
+ create table has_fast_default(f1 int);
+ insert into has_fast_default values(1);
+ alter table has_fast_default add column f2 int default 42;
+ table has_fast_default;
+  f1 | f2
+ ----+----
+   1 | 42
+ (1 row)
+
diff --git a/src/test/regress/sql/fast_default.sql b/src/test/regress/sql/fast_default.sql
index 0e66033..7b9cc47 100644
*** a/src/test/regress/sql/fast_default.sql
--- b/src/test/regress/sql/fast_default.sql
*************** DROP TABLE has_volatile;
*** 369,371 ****
--- 369,378 ----
  DROP EVENT TRIGGER has_volatile_rewrite;
  DROP FUNCTION log_rewrite;
  DROP SCHEMA fast_default;
+
+ -- Leave a table with an active fast default in place, for pg_upgrade testing
+ set search_path = public;
+ create table has_fast_default(f1 int);
+ insert into has_fast_default values(1);
+ alter table has_fast_default add column f2 int default 42;
+ table has_fast_default;