MDEV-17763 Assertion `len == 20U' failed in rec_convert_dtuple_to_rec_comp on DROP COLUMN

btr_cur_pessimistic_insert(): Convert the metadata field of the metadata
record into BLOB before inserting, just like btr_cur_optimistic_insert()
does.

mysql-test/suite/innodb/r/instant_alter.result

@@ -578,6 +578,40 @@ id	f
 1	NULL
 2	NULL
 DROP TABLE t1;
+CREATE TABLE t1 (
+pk INT PRIMARY KEY,
+f1 INT,
+f2 CHAR(255),
+f3 BIGINT,
+f4 INT,
+f5 CHAR(255),
+f6 CHAR(255),
+f7 CHAR(255) NOT NULL,
+f8 INT,
+f9 CHAR(10)
+) ENGINE=InnoDB ROW_FORMAT=REDUNDANT;
+INSERT INTO t1 VALUES
+(1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a'),
+(2, 2, 'b', 2, 2, 'b', 'b', 'b', 2, 'b'),
+(3, 3, 'c', 3, 3, 'c', 'c', 'c', 3, 'c'),
+(4, 4, 'd', 4, 4, 'd', 'd', 'd', 4, 'd'),
+(5, 5, 'e', 5, 5, 'e', 'e', 'e', 5, 'e'),
+(6, 6, 'f', 6, 6, 'f', 'f', 'f', 6, 'f'),
+(7, 7, 'g', 7, 7, 'g', 'g', 'g', 7, 'g'),
+(8, 8, 'h', 8, 8, 'h', 'h', 'h', 8, 'h'),
+(9, 9, 'i', 9, 9, 'i', 'i', 'i', 9, 'i'),
+(10, 0, 'j', 0, 0, 'j', 'j', 'j', 0, 'j'),
+(11, 1, 'k', 1, 1, 'k', 'k', 'k', 1, 'k'),
+(12, 2, 'l', 2, 2, 'l', 'l', 'l', 2, 'l'),
+(13, 3, 'm', 3, 3, 'm', 'm', 'm', 3, 'm'),
+(14, 4, 'n', 4, 4, 'n', 'n', 'n', 4, 'n'),
+(15, 5, 'o', 5, 5, 'o', 'o', 'o', 5, 'o');
+DELETE FROM t1 WHERE pk=1;
+InnoDB		0 transactions not purged
+INSERT INTO t1 VALUES
+(1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a');
+ALTER TABLE t1 DROP COLUMN f1;
+DROP TABLE t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
 c3 POINT NOT NULL DEFAULT ST_GeomFromText('POINT(3 4)'),
@@ -1102,6 +1136,40 @@ id	f
 1	NULL
 2	NULL
 DROP TABLE t1;
+CREATE TABLE t1 (
+pk INT PRIMARY KEY,
+f1 INT,
+f2 CHAR(255),
+f3 BIGINT,
+f4 INT,
+f5 CHAR(255),
+f6 CHAR(255),
+f7 CHAR(255) NOT NULL,
+f8 INT,
+f9 CHAR(10)
+) ENGINE=InnoDB ROW_FORMAT=COMPACT;
+INSERT INTO t1 VALUES
+(1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a'),
+(2, 2, 'b', 2, 2, 'b', 'b', 'b', 2, 'b'),
+(3, 3, 'c', 3, 3, 'c', 'c', 'c', 3, 'c'),
+(4, 4, 'd', 4, 4, 'd', 'd', 'd', 4, 'd'),
+(5, 5, 'e', 5, 5, 'e', 'e', 'e', 5, 'e'),
+(6, 6, 'f', 6, 6, 'f', 'f', 'f', 6, 'f'),
+(7, 7, 'g', 7, 7, 'g', 'g', 'g', 7, 'g'),
+(8, 8, 'h', 8, 8, 'h', 'h', 'h', 8, 'h'),
+(9, 9, 'i', 9, 9, 'i', 'i', 'i', 9, 'i'),
+(10, 0, 'j', 0, 0, 'j', 'j', 'j', 0, 'j'),
+(11, 1, 'k', 1, 1, 'k', 'k', 'k', 1, 'k'),
+(12, 2, 'l', 2, 2, 'l', 'l', 'l', 2, 'l'),
+(13, 3, 'm', 3, 3, 'm', 'm', 'm', 3, 'm'),
+(14, 4, 'n', 4, 4, 'n', 'n', 'n', 4, 'n'),
+(15, 5, 'o', 5, 5, 'o', 'o', 'o', 5, 'o');
+DELETE FROM t1 WHERE pk=1;
+InnoDB		0 transactions not purged
+INSERT INTO t1 VALUES
+(1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a');
+ALTER TABLE t1 DROP COLUMN f1;
+DROP TABLE t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
 c3 POINT NOT NULL DEFAULT ST_GeomFromText('POINT(3 4)'),
@@ -1626,10 +1694,44 @@ id	f
 1	NULL
 2	NULL
 DROP TABLE t1;
+CREATE TABLE t1 (
+pk INT PRIMARY KEY,
+f1 INT,
+f2 CHAR(255),
+f3 BIGINT,
+f4 INT,
+f5 CHAR(255),
+f6 CHAR(255),
+f7 CHAR(255) NOT NULL,
+f8 INT,
+f9 CHAR(10)
+) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;
+INSERT INTO t1 VALUES
+(1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a'),
+(2, 2, 'b', 2, 2, 'b', 'b', 'b', 2, 'b'),
+(3, 3, 'c', 3, 3, 'c', 'c', 'c', 3, 'c'),
+(4, 4, 'd', 4, 4, 'd', 'd', 'd', 4, 'd'),
+(5, 5, 'e', 5, 5, 'e', 'e', 'e', 5, 'e'),
+(6, 6, 'f', 6, 6, 'f', 'f', 'f', 6, 'f'),
+(7, 7, 'g', 7, 7, 'g', 'g', 'g', 7, 'g'),
+(8, 8, 'h', 8, 8, 'h', 'h', 'h', 8, 'h'),
+(9, 9, 'i', 9, 9, 'i', 'i', 'i', 9, 'i'),
+(10, 0, 'j', 0, 0, 'j', 'j', 'j', 0, 'j'),
+(11, 1, 'k', 1, 1, 'k', 'k', 'k', 1, 'k'),
+(12, 2, 'l', 2, 2, 'l', 'l', 'l', 2, 'l'),
+(13, 3, 'm', 3, 3, 'm', 'm', 'm', 3, 'm'),
+(14, 4, 'n', 4, 4, 'n', 'n', 'n', 4, 'n'),
+(15, 5, 'o', 5, 5, 'o', 'o', 'o', 5, 'o');
+DELETE FROM t1 WHERE pk=1;
+InnoDB		0 transactions not purged
+INSERT INTO t1 VALUES
+(1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a');
+ALTER TABLE t1 DROP COLUMN f1;
+DROP TABLE t1;
 disconnect analyze;
 SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 instants
-114
+117
 SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;

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

@@ -447,6 +447,45 @@ ALTER TABLE t1 ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST, ADD KEY(id);
 SELECT * FROM t1;
 DROP TABLE t1;
 
+# MDEV-17763 Assertion `len == 20U' failed in rec_convert_dtuple_to_rec_comp
+# upon DROP COLUMN
+eval CREATE TABLE t1 (
+ pk INT PRIMARY KEY,
+ f1 INT,
+ f2 CHAR(255),
+ f3 BIGINT,
+ f4 INT,
+ f5 CHAR(255),
+ f6 CHAR(255),
+ f7 CHAR(255) NOT NULL,
+ f8 INT,
+ f9 CHAR(10)
+) $engine;
+
+INSERT INTO t1 VALUES
+  (1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a'),
+  (2, 2, 'b', 2, 2, 'b', 'b', 'b', 2, 'b'),
+  (3, 3, 'c', 3, 3, 'c', 'c', 'c', 3, 'c'),
+  (4, 4, 'd', 4, 4, 'd', 'd', 'd', 4, 'd'),
+  (5, 5, 'e', 5, 5, 'e', 'e', 'e', 5, 'e'),
+  (6, 6, 'f', 6, 6, 'f', 'f', 'f', 6, 'f'),
+  (7, 7, 'g', 7, 7, 'g', 'g', 'g', 7, 'g'),
+  (8, 8, 'h', 8, 8, 'h', 'h', 'h', 8, 'h'),
+  (9, 9, 'i', 9, 9, 'i', 'i', 'i', 9, 'i'),
+  (10, 0, 'j', 0, 0, 'j', 'j', 'j', 0, 'j'),
+  (11, 1, 'k', 1, 1, 'k', 'k', 'k', 1, 'k'),
+  (12, 2, 'l', 2, 2, 'l', 'l', 'l', 2, 'l'),
+  (13, 3, 'm', 3, 3, 'm', 'm', 'm', 3, 'm'),
+  (14, 4, 'n', 4, 4, 'n', 'n', 'n', 4, 'n'),
+  (15, 5, 'o', 5, 5, 'o', 'o', 'o', 5, 'o');
+
+DELETE FROM t1 WHERE pk=1;
+--source include/wait_all_purged.inc
+INSERT INTO t1 VALUES
+  (1, 1, 'a', 1, 1, 'a', 'a', 'a', 1, 'a');
+ALTER TABLE t1 DROP COLUMN f1;
+DROP TABLE t1;
+
 dec $format;
 }
 disconnect analyze;

storage/innobase/btr/btr0cur.cc

@@ -3661,10 +3661,16 @@ 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),
 				   dict_table_is_comp(index->table),
 				   dtuple_get_n_fields(entry),
-				   dict_table_page_size(index->table))) {
+				   dict_table_page_size(index->table))
+	    || UNIV_UNLIKELY(entry->is_alter_metadata())) {
 		/* The record is so big that we have to store some fields
 		externally on separate database pages */