MDEV-16065 Assertion failed in btr_pcur_restore_position_func on UPDATE

btr_pcur_store_position(): Assert that the 'default row' record never
is the only record in a page. (If that would happen, an empty
root page would be re-created in the non-instant format, not containing
the special record.) When the cursor is positioned on the page infimum,
never use the 'default row' as the BTR_PCUR_BEFORE reference.
(This is additional cleanup, not fixing the bug.)

rec_copy_prefix_to_buf(): When converting a record prefix to
the non-instant-add format, copy the original number of null flags.
Rename the variable instant_len to instant_omit, and introduce a
few more variables to make the code easiser to read.

Note: In purge, rec_copy_prefix_to_buf() is also used for storing the
persistent cursor position on a 'default row' record. The stored record
reference will be garbage, but row_search_on_row_ref() will do special
handling to reposition the cursor on the 'default row', based on
ref->info_bits.

innodb.dml_purge: Also cover the 'default row'.

1 files changed, 19 insertions, 1 deletions

diff --git a/mysql-test/suite/innodb/r/instant_alter.result b/mysql-test/suite/innodb/r/instant_alter.result
index 1580ba29717..a70a3d077e0 100644
--- a/mysql-test/suite/innodb/r/instant_alter.result
+++ b/mysql-test/suite/innodb/r/instant_alter.result
@@ -440,6 +440,12 @@ SELECT * FROM t1;
 a	b
 a	1
 DROP TABLE t1;
+CREATE TABLE t1 (a INT, b VARCHAR(8), PRIMARY KEY(b,a)) ENGINE=InnoDB ROW_FORMAT=REDUNDANT;
+INSERT INTO t1 VALUES (1,'foo');
+ALTER TABLE t1 ADD COLUMN c INT;
+UPDATE t1 SET c = 1;
+UPDATE t1 SET c = 2;
+DROP TABLE t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
 c3 POINT NOT NULL DEFAULT ST_GeomFromText('POINT(3 4)'),
@@ -826,6 +832,12 @@ SELECT * FROM t1;
 a	b
 a	1
 DROP TABLE t1;
+CREATE TABLE t1 (a INT, b VARCHAR(8), PRIMARY KEY(b,a)) ENGINE=InnoDB ROW_FORMAT=COMPACT;
+INSERT INTO t1 VALUES (1,'foo');
+ALTER TABLE t1 ADD COLUMN c INT;
+UPDATE t1 SET c = 1;
+UPDATE t1 SET c = 2;
+DROP TABLE t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
 c3 POINT NOT NULL DEFAULT ST_GeomFromText('POINT(3 4)'),
@@ -1212,10 +1224,16 @@ SELECT * FROM t1;
 a	b
 a	1
 DROP TABLE t1;
+CREATE TABLE t1 (a INT, b VARCHAR(8), PRIMARY KEY(b,a)) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;
+INSERT INTO t1 VALUES (1,'foo');
+ALTER TABLE t1 ADD COLUMN c INT;
+UPDATE t1 SET c = 1;
+UPDATE t1 SET c = 2;
+DROP TABLE t1;
 disconnect analyze;
 SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 instants
-36
+39
 SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;