MDEV-15563: Instantly change a column to NULL

Allow instant changes of columns in ROW_FORMAT=REDUNDANT
from NOT NULL to NULL.

Later, this may be implemented for ROW_FORMAT=COMPACT or DYNAMIC,
but in that case any indexes on the table must be rebuilt.

dict_table_t::prepare_instant(): Add some debug assertions,
and relax a debug assertion so that the number of fields is
allowed not to change.

dict_index_t::instant_add_field(): Relax a debug assertion,
allowing a column to change from NOT NULL to NULL.

dict_table_t::instant_column(): Add debug assertions.

instant_alter_column_possible(): Allow ALTER_COLUMN_NULLABLE
when applicable.

innodb_insert_sys_columns(): Add the parameter bool update=false
to run UPDATE instead of INSERT.

innobase_instant_add_col(): Remove; let the only caller invoke
innodb_insert_sys_columns() directly.

innobase_instant_try(): Update the SYS_COLUMNS record if the
column is changed. Only convert the table to the instant ALTER TABLE
format if necessary. For ALTER_COLUMN_NULLABLE in ROW_FORMAT=REDUNDANT,
there is no data format change.

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

@@ -612,6 +612,9 @@ 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 (f1 VARCHAR(1), f2 VARCHAR(2)) ENGINE=InnoDB ROW_FORMAT=REDUNDANT;
+ALTER TABLE t1 MODIFY f2 VARCHAR (8) FIRST;
+DROP TABLE t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
 c3 POINT NOT NULL DEFAULT ST_GeomFromText('POINT(3 4)'),
@@ -1170,6 +1173,9 @@ 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 (f1 VARCHAR(1), f2 VARCHAR(2)) ENGINE=InnoDB ROW_FORMAT=COMPACT;
+ALTER TABLE t1 MODIFY f2 VARCHAR (8) FIRST;
+DROP TABLE t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
 c3 POINT NOT NULL DEFAULT ST_GeomFromText('POINT(3 4)'),
@@ -1728,10 +1734,13 @@ 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 (f1 VARCHAR(1), f2 VARCHAR(2)) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;
+ALTER TABLE t1 MODIFY f2 VARCHAR (8) FIRST;
+DROP TABLE t1;
 disconnect analyze;
 SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 instants
-117
+120
 SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;

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

@@ -0,0 +1,56 @@
+create table t (a int NOT NULL) engine=innodb row_format=   compressed;
+alter table t modify a int NULL, algorithm=instant;
+ERROR 0A000: ALGORITHM=INSTANT is not supported for this operation. Try ALGORITHM=INPLACE
+drop table t;
+create table t (a int NOT NULL) engine=innodb row_format=   dynamic;
+alter table t modify a int NULL, algorithm=instant;
+ERROR 0A000: ALGORITHM=INSTANT is not supported for this operation. Try ALGORITHM=INPLACE
+drop table t;
+create table t (a int NOT NULL) engine=innodb row_format=   compact;
+alter table t modify a int NULL, algorithm=instant;
+ERROR 0A000: ALGORITHM=INSTANT is not supported for this operation. Try ALGORITHM=INPLACE
+drop table t;
+create table t (
+id int primary key,
+a int NOT NULL default 0,
+b int NOT NULL default 0,
+c int NOT NULL default 0,
+index idx (a,b,c)
+) engine=innodb row_format=redundant;
+insert into t (id, a) values (0, NULL);
+ERROR 23000: Column 'a' cannot be null
+insert into t (id, b) values (0, NULL);
+ERROR 23000: Column 'b' cannot be null
+insert into t (id, c) values (0, NULL);
+ERROR 23000: Column 'c' cannot be null
+insert into t values (1,1,1,1);
+set @id = (select table_id from information_schema.innodb_sys_tables
+where name = 'test/t');
+select * from information_schema.innodb_sys_columns where table_id=@id;
+TABLE_ID	NAME	POS	MTYPE	PRTYPE	LEN
+TABLE_ID	id	0	6	1283	4
+TABLE_ID	a	1	6	1283	4
+TABLE_ID	b	2	6	1283	4
+TABLE_ID	c	3	6	1283	4
+alter table t modify a int NULL, algorithm=instant;
+insert into t values (2, NULL, 2, 2);
+alter table t modify b int NULL, algorithm=nocopy;
+insert into t values (3, NULL, NULL, 3);
+alter table t modify c int NULL, algorithm=inplace;
+insert into t values (4, NULL, NULL, NULL);
+select * from information_schema.innodb_sys_columns where table_id=@id;
+TABLE_ID	NAME	POS	MTYPE	PRTYPE	LEN
+TABLE_ID	id	0	6	1283	4
+TABLE_ID	a	1	6	1027	4
+TABLE_ID	b	2	6	1027	4
+TABLE_ID	c	3	6	1027	4
+select * from t;
+id	a	b	c
+4	NULL	NULL	NULL
+3	NULL	NULL	3
+2	NULL	2	2
+1	1	1	1
+check table t;
+Table	Op	Msg_type	Msg_text
+test.t	check	status	OK
+drop table t;

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

@@ -486,6 +486,10 @@ INSERT INTO t1 VALUES
 ALTER TABLE t1 DROP COLUMN f1;
 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;
+
 dec $format;
 }
 disconnect analyze;

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

@@ -0,0 +1,57 @@
+--source include/have_innodb.inc
+
+create table t (a int NOT NULL) engine=innodb row_format=   compressed;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED
+alter table t modify a int NULL, algorithm=instant;
+drop table t;
+
+create table t (a int NOT NULL) engine=innodb row_format=   dynamic;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED
+alter table t modify a int NULL, algorithm=instant;
+drop table t;
+
+create table t (a int NOT NULL) engine=innodb row_format=   compact;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED
+alter table t modify a int NULL, algorithm=instant;
+drop table t;
+
+create table t (
+  id int primary key,
+  a int NOT NULL default 0,
+  b int NOT NULL default 0,
+  c int NOT NULL default 0,
+  index idx (a,b,c)
+) engine=innodb row_format=redundant;
+
+--error ER_BAD_NULL_ERROR
+insert into t (id, a) values (0, NULL);
+--error ER_BAD_NULL_ERROR
+insert into t (id, b) values (0, NULL);
+--error ER_BAD_NULL_ERROR
+insert into t (id, c) values (0, NULL);
+
+insert into t values (1,1,1,1);
+
+set @id = (select table_id from information_schema.innodb_sys_tables
+where name = 'test/t');
+
+--replace_column 1 TABLE_ID
+select * from information_schema.innodb_sys_columns where table_id=@id;
+
+alter table t modify a int NULL, algorithm=instant;
+insert into t values (2, NULL, 2, 2);
+
+alter table t modify b int NULL, algorithm=nocopy;
+insert into t values (3, NULL, NULL, 3);
+
+alter table t modify c int NULL, algorithm=inplace;
+insert into t values (4, NULL, NULL, NULL);
+
+--replace_column 1 TABLE_ID
+select * from information_schema.innodb_sys_columns where table_id=@id;
+
+select * from t;
+
+check table t;
+
+drop table t;