amcheck: Normalize index tuples containing uncompressed varlena

It might happen that the varlena value wasn't compressed by index_form_tuple()
due to current storage parameters.  If compression is currently enabled, we
need to compress such values to match index tuple coming from the heap.

Backpatch to all supported versions.

Discussion: https://postgr.es/m/flat/7bdbe559-d61a-4ae4-a6e1-48abdf3024cc%40postgrespro.ru
Author: Andrey Borodin
Reviewed-by: Alexander Lakhin, Michael Zhilin, Jian He, Alexander Korotkov
Backpatch-through: 12

Author: akorotkov

contrib/amcheck/expected/check_btree.out

@@ -202,6 +202,16 @@ SELECT bt_index_check('varlena_bug_idx', true);
 
 (1 row)
 
+-- Also check that we compress varlena values, which were previously stored
+-- uncompressed in index.
+INSERT INTO varlena_bug VALUES (repeat('Test', 250));
+ALTER TABLE varlena_bug ALTER COLUMN v SET STORAGE extended;
+SELECT bt_index_check('varlena_bug_idx', true);
+ bt_index_check 
+----------------
+ 
+(1 row)
+
 -- cleanup
 DROP TABLE bttest_a;
 DROP TABLE bttest_b;

contrib/amcheck/sql/check_btree.sql

@@ -140,6 +140,12 @@ x
 CREATE INDEX varlena_bug_idx on varlena_bug(v);
 SELECT bt_index_check('varlena_bug_idx', true);
 
+-- Also check that we compress varlena values, which were previously stored
+-- uncompressed in index.
+INSERT INTO varlena_bug VALUES (repeat('Test', 250));
+ALTER TABLE varlena_bug ALTER COLUMN v SET STORAGE extended;
+SELECT bt_index_check('varlena_bug_idx', true);
+
 -- cleanup
 DROP TABLE bttest_a;
 DROP TABLE bttest_b;

contrib/amcheck/verify_nbtree.c

@@ -28,6 +28,7 @@
 #include "access/table.h"
 #include "access/tableam.h"
 #include "access/transam.h"
+#include "access/tuptoaster.h"
 #include "access/xact.h"
 #include "catalog/index.h"
 #include "catalog/pg_am.h"
@@ -2093,6 +2094,18 @@ bt_normalize_tuple(BtreeCheckState *state, IndexTuple itup)
 							ItemPointerGetBlockNumber(&(itup->t_tid)),
 							ItemPointerGetOffsetNumber(&(itup->t_tid)),
 							RelationGetRelationName(state->rel))));
+		else if (!VARATT_IS_COMPRESSED(DatumGetPointer(normalized[i])) &&
+				 VARSIZE(DatumGetPointer(normalized[i])) > TOAST_INDEX_TARGET &&
+				 (att->attstorage == 'x' ||
+				  att->attstorage == 'm'))
+		{
+			/*
+			 * This value will be compressed by index_form_tuple() with the
+			 * current storage settings.  We may be here because this tuple
+			 * was formed with different storage settings.  So, force forming.
+			 */
+			formnewtup = true;
+		}
 		else if (VARATT_IS_COMPRESSED(DatumGetPointer(normalized[i])))
 		{
 			formnewtup = true;