MDEV-17820 Assertion failed on instant DROP COLUMN

btr_cur_pessimistic_insert(): Do not attempt to convert the
metadata BLOB to external storage if it has already been converted.
It could have been converted by btr_cur_pessimistic_update().
Relax some over-zealous assertions.

dtuple_convert_big_rec(): Assert that the metadata BLOB has
not been converted yet.

mysql-test/suite/innodb/t/instant_alter.test

@@ -498,6 +498,70 @@ INSERT INTO t1 VALUES
 ALTER TABLE t1 DROP COLUMN f1;
 DROP TABLE t1;
 
+# MDEV-17820 Assertion failures on DROP COLUMN
+eval CREATE TABLE t1 (
+  pk INT PRIMARY KEY,
+  f1 INT, f2 CHAR(32) NOT NULL,
+  f3 INT NOT NULL, f4 INT NOT NULL, f5 INT, f6 CHAR(32) NOT NULL,
+  f7 CHAR(32), f8 CHAR(32)
+) $engine;
+
+INSERT INTO t1 VALUES
+  (1,9,'',2,88,88,'','',''),(2,48,'',8,68,92,'','',''),
+  (3,41,'',56,84,37,'','',''),(4,NULL,'',6,6,NULL,'','',''),
+  (5,52,'',37,44,20,'','',''),(6,44,'',53,4,NULL,'','',''),
+  (7,24,'',54,8,54,'','',''),(8,80,'',3,52,20,'','',''),
+  (9,71,'',34,32,NULL,'','',''),(10,14,'',6,64,88,'','',''),
+  (11,48,'',8,25,42,'','',''),(12,16,'',8,7,NULL,'','',''),
+  (13,NULL,'',22,0,95,'','',''),(14,4,'',72,48,NULL,'','',''),
+  (15,4,'',5,64,2,'','',''),(16,NULL,'',9,40,30,'','',''),
+  (17,92,'',48,2,NULL,'','',''),(18,36,'',48,51,7,'','',''),
+  (19,NULL,'',80,96,NULL,'','',''),(20,96,'',9,80,NULL,'','',''),
+  (21,50,'',16,40,NULL,'','',''),(22,NULL,'',7,84,8,'','',''),
+  (23,28,'',93,80,NULL,'','',''),(24,31,'',40,38,NULL,'','',''),
+  (25,85,'',8,5,88,'','',''),(26,66,'',8,32,4,'','',''),
+  (51,52,'',6,92,15,'','',''),(52,77,'',24,24,28,'','',''),
+  (53,8,'',75,31,NULL,'','',''),(54,48,'',5,8,1,'','',''),
+  (55,90,'',56,12,5,'','',''),(56,92,'',4,9,88,'','',''),
+  (57,83,'',23,40,72,'','',''),(58,7,'',4,40,32,'','',''),
+  (59,28,'',2,3,32,'','',''),(60,16,'',80,4,NULL,'','',''),
+  (61,44,'',88,24,NULL,'','',''),(62,4,'',5,25,3,'','',''),
+  (63,NULL,'',7,24,76,'','',''),(64,0,'',13,40,73,'','',''),
+  (101,NULL,'',1,49,75,'','',''),(102,34,'',10,17,20,'','',''),
+  (103,8,'',2,2,NULL,'','',''),(104,12,'',44,48,52,'','',''),
+  (105,8,'',4,19,38,'','',''),(106,20,'',6,80,9,'','',''),
+  (107,72,'',72,16,56,'','',''),(108,76,'',98,24,21,'','',''),
+  (109,67,'',16,91,NULL,'','',''),(110,72,'',72,3,48,'','',''),
+  (151,8,'',3,86,NULL,'','',''),(152,NULL,'',52,72,0,'','',''),
+  (153,NULL,'',46,30,92,'','',''),(154,80,'',1,40,48,'','',''),
+  (155,24,'',68,68,8,'','',''),(156,85,'',85,72,60,'','',''),
+  (157,7,'',7,12,6,'','',''),(158,NULL,'',48,48,80,'','',''),
+  (159,12,'',0,36,0,'','',''),(160,2,'',6,52,NULL,'','',''),
+  (201,0,'',1,3,NULL,'','',''),(202,NULL,'',3,53,14,'','',''),
+  (203,84,'',6,20,NULL,'','',''),(204,38,'',25,13,88,'','',''),
+  (205,1,'',2,69,5,'','',''),(206,7,'',60,22,NULL,'','',''),
+  (207,NULL,'',5,4,NULL,'','',''),(251,7,'',0,4,40,'','',''),
+  (252,4,'',16,8,NULL,'','',''),(253,14,'',60,12,99,'','',''),
+  (254,84,'',68,16,5,'','',''),(255,3,'',70,36,61,'','',''),
+  (256,7,'',18,48,NULL,'','',''),(257,NULL,'',68,53,NULL,'','',''),
+  (258,29,'',52,16,64,'','',''),(259,NULL,'',80,92,40,'','',''),
+  (301,68,'',1,48,48,'','',''),(302,2,'',1,1,32,'','',''),
+  (303,44,'',60,96,16,'','',''),(304,32,'',52,64,32,'','',''),
+  (305,88,'',37,72,NULL,'','',''),(306,5,'',35,60,20,'','',''),
+  (307,35,'',4,48,NULL,'','',''),(308,4,'',92,44,80,'','',''),
+  (351,48,'',60,4,40,'','',''),(352,7,'',9,61,13,'','',''),
+  (353,0,'',5,93,53,'','',''),(354,7,'',1,20,NULL,'','',''),
+  (355,84,'',5,48,96,'','',''),(356,NULL,'',39,92,36,'','',''),
+  (357,88,'',9,76,44,'','',''),(358,66,'',34,67,80,'','',''),
+  (359,8,'',8,52,NULL,'','',''),(360,3,'',53,83,NULL,'','',''),
+  (361,23,'',44,9,48,'','',''),(362,4,'',0,54,48,'','',''),
+  (363,75,'',66,76,52,'','','');
+
+ALTER TABLE t1 ADD COLUMN x VARCHAR(255) DEFAULT ' foobar ';
+UPDATE t1 SET f1 = 0;
+ALTER TABLE t1 DROP COLUMN x;
+DROP TABLE t1;
+
 eval CREATE TABLE t1 (f1 VARCHAR(1), f2 VARCHAR(2)) $engine;
 ALTER TABLE t1 MODIFY f2 VARCHAR (8) FIRST;
 DROP TABLE t1;

storage/innobase/btr/btr0cur.cc

@@ -3,7 +3,7 @@
 Copyright (c) 1994, 2018, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, Google Inc.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2015, 2018, MariaDB Corporation.
+Copyright (c) 2015, 2019, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -3693,16 +3693,15 @@ btr_cur_pessimistic_insert(
 		}
 	}
 
-	DBUG_ASSERT(!entry->is_alter_metadata()
-		    || !dfield_is_ext(
-			    dtuple_get_nth_field(entry,
-						 index->first_user_field())));
-
 	if (page_zip_rec_needs_ext(rec_get_converted_size(index, entry, n_ext),
 				   index->table->not_redundant(),
 				   dtuple_get_n_fields(entry),
 				   btr_cur_get_block(cursor)->page.size)
-	    || UNIV_UNLIKELY(entry->is_alter_metadata())) {
+	    || UNIV_UNLIKELY(entry->is_alter_metadata()
+			     && !dfield_is_ext(
+				     dtuple_get_nth_field(
+					     entry,
+					     index->first_user_field())))) {
 		/* The record is so big that we have to store some fields
 		externally on separate database pages */
 
@@ -3777,8 +3776,8 @@ btr_cur_pessimistic_insert(
 		if (entry->info_bits & REC_INFO_MIN_REC_FLAG) {
 			ut_ad(entry->is_metadata());
 			ut_ad(index->is_instant());
-			ut_ad((flags & ulint(~BTR_KEEP_IBUF_BITMAP))
-			      == BTR_NO_LOCKING_FLAG);
+			ut_ad(flags & BTR_NO_LOCKING_FLAG);
+			ut_ad(!(flags & BTR_CREATE_FLAG));
 		} else {
 			btr_search_update_hash_on_insert(
 				cursor, btr_get_search_latch(index));

storage/innobase/data/data0data.cc

 /*****************************************************************************
 
 Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2018, MariaDB Corporation.
+Copyright (c) 2017, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -643,6 +643,7 @@ dtuple_convert_big_rec(
 		longest_i = index->first_user_field();
 		dfield = dtuple_get_nth_field(entry, longest_i);
 		local_len = BTR_EXTERN_FIELD_REF_SIZE;
+		ut_ad(!dfield_is_ext(dfield));
 		goto ext_write;
 	}