fix main.mysql57_virtual, main.alter_table, innodb.alter_algorithm

The correct (best) algorithm is now chosen for ALGORITHM=DEFAULT
and alter_algorithm=DEFAULT

See also MDEV-30906

mysql-test/main/alter_table.result

@@ -1662,8 +1662,8 @@ ALTER TABLE t1 ADD INDEX i1(b);
 affected rows: 2
 info: Records: 2  Duplicates: 0  Warnings: 0
 ALTER TABLE t1 ADD INDEX i2(b), ALGORITHM= DEFAULT;
-affected rows: 2
-info: Records: 2  Duplicates: 0  Warnings: 1
+affected rows: 0
+info: Records: 0  Duplicates: 0  Warnings: 1
 Warnings:
 Note	1831	Duplicate index `i2`. This is deprecated and will be disallowed in a future release
 ALTER TABLE t1 ADD INDEX i3(b), ALGORITHM= COPY;

mysql-test/main/mysql57_virtual.result

@@ -14,7 +14,7 @@ a	b	c
 1	2	4
 2	3	5
 alter online table mysql57_virtual comment "I am now a MariaDB table", algorithm=nocopy;
-ERROR 0A000: LOCK=NONE is not supported. Reason: COPY algorithm requires a lock. Try LOCK=SHARED
+ERROR 0A000: ALGORITHM=INPLACE is not supported for this operation. Try ALGORITHM=COPY
 alter table mysql57_virtual comment "I am now a MariaDB table";
 SHOW CREATE TABLE mysql57_virtual;
 Table	Create Table

mysql-test/main/mysql57_virtual.test

@@ -13,7 +13,7 @@ insert into mysql57_virtual (a) values (1),(2);
 select * from mysql57_virtual;
 
 # We can't do online changes, as the MariaDB storage is incompatible with MySQL
---error ER_ALTER_OPERATION_NOT_SUPPORTED_REASON
+--error ER_ALTER_OPERATION_NOT_SUPPORTED
 alter online table mysql57_virtual comment "I am now a MariaDB table", algorithm=nocopy;
 
 alter table mysql57_virtual comment "I am now a MariaDB table";

mysql-test/suite/innodb/r/alter_algorithm,INPLACE.rdiff

 --- alter_algorithm.result
 +++ alter_algorithm.reject
-@@ -7,43 +7,43 @@
+@@ -7,40 +7,40 @@
  INSERT INTO t1(f1, f2, f3) VALUES(1, 1, 1);
  SELECT @@alter_algorithm;
  @@alter_algorithm
@@ -56,13 +56,8 @@
 +affected rows: 0
 +info: Records: 0  Duplicates: 0  Warnings: 0
  ALTER TABLE t1 FORCE, ALGORITHM=DEFAULT;
--affected rows: 1
--info: Records: 1  Duplicates: 0  Warnings: 0
-+affected rows: 0
-+info: Records: 0  Duplicates: 0  Warnings: 0
- DROP TABLE t1;
  affected rows: 0
- CREATE TABLE t1(f1 INT PRIMARY KEY, f2 INT NOT NULL,
+ info: Records: 0  Duplicates: 0  Warnings: 0
 @@ -56,22 +56,22 @@
  FOREIGN KEY fidx(f1) REFERENCES t1(f1))ENGINE=INNODB;
  INSERT INTO t1(f1, f2, f4, f5) VALUES(1, 2, 3, 4);

mysql-test/suite/innodb/r/alter_algorithm,INSTANT.rdiff

 --- alter_algorithm.result
 +++ alter_algorithm.reject
-@@ -7,43 +7,35 @@
+@@ -7,40 +7,32 @@
  INSERT INTO t1(f1, f2, f3) VALUES(1, 1, 1);
  SELECT @@alter_algorithm;
  @@alter_algorithm
@@ -48,13 +48,8 @@
 -info: Records: 1  Duplicates: 0  Warnings: 0
 +Got one of the listed errors
  ALTER TABLE t1 FORCE, ALGORITHM=DEFAULT;
--affected rows: 1
--info: Records: 1  Duplicates: 0  Warnings: 0
-+affected rows: 0
-+info: Records: 0  Duplicates: 0  Warnings: 0
- DROP TABLE t1;
  affected rows: 0
- CREATE TABLE t1(f1 INT PRIMARY KEY, f2 INT NOT NULL,
+ info: Records: 0  Duplicates: 0  Warnings: 0
 @@ -56,22 +48,17 @@
  FOREIGN KEY fidx(f1) REFERENCES t1(f1))ENGINE=INNODB;
  INSERT INTO t1(f1, f2, f4, f5) VALUES(1, 2, 3, 4);

mysql-test/suite/innodb/r/alter_algorithm,NOCOPY.rdiff

 --- alter_algorithm.result
 +++ alter_algorithm.reject
-@@ -7,43 +7,35 @@
+@@ -7,40 +7,32 @@
  INSERT INTO t1(f1, f2, f3) VALUES(1, 1, 1);
  SELECT @@alter_algorithm;
  @@alter_algorithm
@@ -48,13 +48,8 @@
 -info: Records: 1  Duplicates: 0  Warnings: 0
 +Got one of the listed errors
  ALTER TABLE t1 FORCE, ALGORITHM=DEFAULT;
--affected rows: 1
--info: Records: 1  Duplicates: 0  Warnings: 0
-+affected rows: 0
-+info: Records: 0  Duplicates: 0  Warnings: 0
- DROP TABLE t1;
  affected rows: 0
- CREATE TABLE t1(f1 INT PRIMARY KEY, f2 INT NOT NULL,
+ info: Records: 0  Duplicates: 0  Warnings: 0
 @@ -56,22 +48,22 @@
  FOREIGN KEY fidx(f1) REFERENCES t1(f1))ENGINE=INNODB;
  INSERT INTO t1(f1, f2, f4, f5) VALUES(1, 2, 3, 4);

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

@@ -42,8 +42,8 @@ ALTER TABLE t1 ENGINE=INNODB;
 affected rows: 1
 info: Records: 1  Duplicates: 0  Warnings: 0
 ALTER TABLE t1 FORCE, ALGORITHM=DEFAULT;
-affected rows: 1
-info: Records: 1  Duplicates: 0  Warnings: 0
+affected rows: 0
+info: Records: 0  Duplicates: 0  Warnings: 0
 DROP TABLE t1;
 affected rows: 0
 CREATE TABLE t1(f1 INT PRIMARY KEY, f2 INT NOT NULL,

mysql-test/suite/versioning/r/online.result

@@ -7,7 +7,7 @@ ERROR 0A000: ALGORITHM=INPLACE is not supported. Reason: Not implemented for sys
 alter table t add system versioning, lock=shared;
 alter table t add column b int, change column a a int without system versioning, lock=none;
 alter table t drop system versioning, lock=none;
-ERROR 0A000: LOCK=NONE is not supported. Reason: Not implemented for system-versioned operations. Try LOCK=SHARED
+ERROR 0A000: LOCK=NONE is not supported. Reason: DROP SYSTEM VERSIONING. Try LOCK=SHARED
 alter table t drop system versioning, algorithm=inplace;
 create or replace table t (
 a int, b int,
@@ -127,7 +127,7 @@ alter table t drop column b, algorithm=instant;
 alter table t add index idx(a), lock=none;
 alter table t drop column s, drop column e;
 alter table t drop system versioning, lock=none;
-ERROR 0A000: LOCK=NONE is not supported. Reason: Not implemented for system-versioned operations. Try LOCK=SHARED
+ERROR 0A000: LOCK=NONE is not supported. Reason: DROP SYSTEM VERSIONING. Try LOCK=SHARED
 #
 # MDEV-17697 Broken versioning info after instant drop column
 #

sql/sql_alter.cc

@@ -260,6 +260,14 @@ Alter_info::algorithm(const THD *thd) const
   return requested_algorithm;
 }
 
+bool Alter_info::algorithm_is_nocopy(const THD *thd) const
+{
+  auto alg= algorithm(thd);
+  return alg == ALTER_TABLE_ALGORITHM_INPLACE
+         || alg == ALTER_TABLE_ALGORITHM_INSTANT
+         || alg == ALTER_TABLE_ALGORITHM_NOCOPY;
+}
+
 
 Alter_table_ctx::Alter_table_ctx()
   : db(null_clex_str), table_name(null_clex_str), alias(null_clex_str),

sql/sql_alter.h

@@ -233,6 +233,7 @@ class Alter_info
     algorithm then return alter_algorithm variable value.
    */
   enum_alter_table_algorithm algorithm(const THD *thd) const;
+  bool algorithm_is_nocopy(const THD *thd) const;
 
 private:
   Alter_info &operator=(const Alter_info &rhs); // not implemented

sql/sql_table.cc

@@ -10676,31 +10676,25 @@ do_continue:;
 #endif
 
   /*
-    Use copy algorithm if:
-    - old_alter_table system variable is set without in-place requested using
-      the ALGORITHM clause.
-    - Or if in-place is impossible for given operation.
+    We can use only copy algorithm if one of the following is true:
+    - In-place is impossible for given operation.
     - Changes to partitioning which were not handled by fast_alter_part_table()
       needs to be handled using table copying algorithm unless the engine
       supports auto-partitioning as such engines can do some changes
       using in-place API.
   */
-  if ((thd->variables.alter_algorithm == Alter_info::ALTER_TABLE_ALGORITHM_COPY &&
-       alter_info->algorithm(thd) !=
-       Alter_info::ALTER_TABLE_ALGORITHM_INPLACE)
-      || is_inplace_alter_impossible(table, create_info, alter_info)
+  if (is_inplace_alter_impossible(table, create_info, alter_info)
       || IF_PARTITIONING((partition_changed &&
-          !(old_db_type->partition_flags() & HA_USE_AUTO_PARTITION)), 0))
+                          !(old_db_type->partition_flags() & HA_USE_AUTO_PARTITION)), 0))
   {
-    if (alter_info->algorithm(thd) ==
-        Alter_info::ALTER_TABLE_ALGORITHM_INPLACE)
+    if (alter_info->algorithm_is_nocopy(thd))
     {
       my_error(ER_ALTER_OPERATION_NOT_SUPPORTED, MYF(0),
                "ALGORITHM=INPLACE", "ALGORITHM=COPY");
       DBUG_RETURN(true);
     }
-    alter_info->set_requested_algorithm(
-      Alter_info::ALTER_TABLE_ALGORITHM_COPY);
+
+    alter_info->set_requested_algorithm(Alter_info::ALTER_TABLE_ALGORITHM_COPY);
   }
 
   /*