Apply stopgap fix for bug #15672.

Fix DefineIndex so that it doesn't attempt to pass down a to-be-reused
index relfilenode to a child index creation, and fix TryReuseIndex
to not think that reuse is sensible for a partitioned index.

In v11, this fixes a problem where ALTER TABLE on a partitioned table
could assign the same relfilenode to several different child indexes,
causing very nasty catalog corruption --- in fact, attempting to DROP
the partitioned table then leads not only to a database crash, but to
inability to restart because the same crash will recur during WAL replay.

Either of these two changes would be enough to prevent the failure, but
since neither action could possibly be sane, let's put in both changes
for future-proofing.

In HEAD, no such bug manifests, but that's just an accidental consequence
of having changed the pg_class representation of partitioned indexes to
have relfilenode = 0.  Both of these changes still seem like smart
future-proofing.

This is only a stop-gap because the code for ALTER TABLE on a partitioned
table with a no-op type change still leaves a great deal to be desired.
As the added regression tests show, it gets things wrong for comments on
child indexes/constraints, and it is regenerating child indexes it doesn't
have to.  However, fixing those problems will take more work which may not
get back-patched into v11.  We need a fix for the corruption problem now.

Per bug #15672 from Jianing Yang.

Patch by me, regression test cases based on work by Amit Langote,
who also did a lot of the investigative work.

Discussion: https://postgr.es/m/15672-b9fa7db32698269f@postgresql.org

src/backend/commands/indexcmds.c

@@ -1150,6 +1150,18 @@ DefineIndex(Oid relationId,
 					bool		found_whole_row;
 					ListCell   *lc;
 
+					/*
+					 * We can't use the same index name for the child index,
+					 * so clear idxname to let the recursive invocation choose
+					 * a new name.  Likewise, the existing target relation
+					 * field is wrong, and if indexOid or oldNode are set,
+					 * they mustn't be applied to the child either.
+					 */
+					childStmt->idxname = NULL;
+					childStmt->relation = NULL;
+					childStmt->indexOid = InvalidOid;
+					childStmt->oldNode = InvalidOid;
+
 					/*
 					 * Adjust any Vars (both in expressions and in the index's
 					 * WHERE clause) to match the partition's column numbering
@@ -1181,8 +1193,6 @@ DefineIndex(Oid relationId,
 					if (found_whole_row)
 						elog(ERROR, "cannot convert whole-row table reference");
 
-					childStmt->idxname = NULL;
-					childStmt->relation = NULL;
 					DefineIndex(childRelid, childStmt,
 								InvalidOid, /* no predefined OID */
 								indexRelationId,	/* this is our child */

src/backend/commands/tablecmds.c

@@ -11452,6 +11452,8 @@ TryReuseIndex(Oid oldId, IndexStmt *stmt)
 	{
 		Relation	irel = index_open(oldId, NoLock);
 
+		/* If it's a partitioned index, there is no storage to share. */
+		if (irel->rd_rel->relkind != RELKIND_PARTITIONED_INDEX)
 			stmt->oldNode = irel->rd_node.relNode;
 		index_close(irel, NoLock);
 	}

src/test/regress/expected/alter_table.out

@@ -1990,6 +1990,94 @@ Indexes:
     "at_part_2_a_idx" btree (a)
     "at_part_2_b_idx" btree (b)
 
+drop table at_partitioned;
+-- Alter column type when no table rewrite is required
+-- Also check that comments are preserved
+create table at_partitioned(id int, name varchar(64), unique (id, name))
+  partition by hash(id);
+comment on constraint at_partitioned_id_name_key on at_partitioned is 'parent constraint';
+comment on index at_partitioned_id_name_key is 'parent index';
+create table at_partitioned_0 partition of at_partitioned
+  for values with (modulus 2, remainder 0);
+comment on constraint at_partitioned_0_id_name_key on at_partitioned_0 is 'child 0 constraint';
+comment on index at_partitioned_0_id_name_key is 'child 0 index';
+create table at_partitioned_1 partition of at_partitioned
+  for values with (modulus 2, remainder 1);
+comment on constraint at_partitioned_1_id_name_key on at_partitioned_1 is 'child 1 constraint';
+comment on index at_partitioned_1_id_name_key is 'child 1 index';
+insert into at_partitioned values(1, 'foo');
+insert into at_partitioned values(3, 'bar');
+create temp table old_oids as
+  select relname, oid as oldoid, relfilenode as oldfilenode
+  from pg_class where relname like 'at_partitioned%';
+select relname,
+  c.oid = oldoid as orig_oid,
+  case relfilenode
+    when 0 then 'none'
+    when c.oid then 'own'
+    when oldfilenode then 'orig'
+    else 'OTHER'
+    end as storage,
+  obj_description(c.oid, 'pg_class') as desc
+  from pg_class c left join old_oids using (relname)
+  where relname like 'at_partitioned%'
+  order by relname;
+           relname            | orig_oid | storage |     desc      
+------------------------------+----------+---------+---------------
+ at_partitioned               | t        | none    | 
+ at_partitioned_0             | t        | own     | 
+ at_partitioned_0_id_name_key | t        | own     | child 0 index
+ at_partitioned_1             | t        | own     | 
+ at_partitioned_1_id_name_key | t        | own     | child 1 index
+ at_partitioned_id_name_key   | t        | none    | parent index
+(6 rows)
+
+select conname, obj_description(oid, 'pg_constraint') as desc
+  from pg_constraint where conname like 'at_partitioned%'
+  order by conname;
+           conname            |        desc        
+------------------------------+--------------------
+ at_partitioned_0_id_name_key | child 0 constraint
+ at_partitioned_1_id_name_key | child 1 constraint
+ at_partitioned_id_name_key   | parent constraint
+(3 rows)
+
+alter table at_partitioned alter column name type varchar(127);
+-- Note: these tests currently show the wrong behavior for comments :-(
+select relname,
+  c.oid = oldoid as orig_oid,
+  case relfilenode
+    when 0 then 'none'
+    when c.oid then 'own'
+    when oldfilenode then 'orig'
+    else 'OTHER'
+    end as storage,
+  obj_description(c.oid, 'pg_class') as desc
+  from pg_class c left join old_oids using (relname)
+  where relname like 'at_partitioned%'
+  order by relname;
+           relname            | orig_oid | storage |     desc     
+------------------------------+----------+---------+--------------
+ at_partitioned               | t        | none    | 
+ at_partitioned_0             | t        | own     | 
+ at_partitioned_0_id_name_key | f        | own     | parent index
+ at_partitioned_1             | t        | own     | 
+ at_partitioned_1_id_name_key | f        | own     | parent index
+ at_partitioned_id_name_key   | f        | none    | parent index
+(6 rows)
+
+select conname, obj_description(oid, 'pg_constraint') as desc
+  from pg_constraint where conname like 'at_partitioned%'
+  order by conname;
+           conname            |       desc        
+------------------------------+-------------------
+ at_partitioned_0_id_name_key | 
+ at_partitioned_1_id_name_key | 
+ at_partitioned_id_name_key   | parent constraint
+(3 rows)
+
+-- Don't remove this DROP, it exposes bug #15672
+drop table at_partitioned;
 -- disallow recursive containment of row types
 create temp table recur1 (f1 int);
 alter table recur1 add column f2 recur1; -- fails

src/test/regress/sql/alter_table.sql

@@ -1353,6 +1353,69 @@ alter table at_partitioned attach partition at_part_2 for values from (1000) to
 alter table at_partitioned alter column b type numeric using b::numeric;
 \d at_part_1
 \d at_part_2
+drop table at_partitioned;
+
+-- Alter column type when no table rewrite is required
+-- Also check that comments are preserved
+create table at_partitioned(id int, name varchar(64), unique (id, name))
+  partition by hash(id);
+comment on constraint at_partitioned_id_name_key on at_partitioned is 'parent constraint';
+comment on index at_partitioned_id_name_key is 'parent index';
+create table at_partitioned_0 partition of at_partitioned
+  for values with (modulus 2, remainder 0);
+comment on constraint at_partitioned_0_id_name_key on at_partitioned_0 is 'child 0 constraint';
+comment on index at_partitioned_0_id_name_key is 'child 0 index';
+create table at_partitioned_1 partition of at_partitioned
+  for values with (modulus 2, remainder 1);
+comment on constraint at_partitioned_1_id_name_key on at_partitioned_1 is 'child 1 constraint';
+comment on index at_partitioned_1_id_name_key is 'child 1 index';
+insert into at_partitioned values(1, 'foo');
+insert into at_partitioned values(3, 'bar');
+
+create temp table old_oids as
+  select relname, oid as oldoid, relfilenode as oldfilenode
+  from pg_class where relname like 'at_partitioned%';
+
+select relname,
+  c.oid = oldoid as orig_oid,
+  case relfilenode
+    when 0 then 'none'
+    when c.oid then 'own'
+    when oldfilenode then 'orig'
+    else 'OTHER'
+    end as storage,
+  obj_description(c.oid, 'pg_class') as desc
+  from pg_class c left join old_oids using (relname)
+  where relname like 'at_partitioned%'
+  order by relname;
+
+select conname, obj_description(oid, 'pg_constraint') as desc
+  from pg_constraint where conname like 'at_partitioned%'
+  order by conname;
+
+alter table at_partitioned alter column name type varchar(127);
+
+-- Note: these tests currently show the wrong behavior for comments :-(
+
+select relname,
+  c.oid = oldoid as orig_oid,
+  case relfilenode
+    when 0 then 'none'
+    when c.oid then 'own'
+    when oldfilenode then 'orig'
+    else 'OTHER'
+    end as storage,
+  obj_description(c.oid, 'pg_class') as desc
+  from pg_class c left join old_oids using (relname)
+  where relname like 'at_partitioned%'
+  order by relname;
+
+select conname, obj_description(oid, 'pg_constraint') as desc
+  from pg_constraint where conname like 'at_partitioned%'
+  order by conname;
+
+-- Don't remove this DROP, it exposes bug #15672
+drop table at_partitioned;
 
 -- disallow recursive containment of row types
 create temp table recur1 (f1 int);