MDEV-16288 ALTER TABLE…ALGORITHM=DEFAULT does not override alter_algorithm

- ALTER_ALGORITHM should be substituted when there is no mention of
algorithm in alter statement.
- Introduced algorithm(thd) in Alter_info. It returns the
user requested algorithm. If user doesn't specify algorithm explicitly then
it returns alter_algorithm variable.
- changed algorithm() to get_algorithm(thd) to return algorithm name for
displaying the error.
- set_requested_algorithm(algo_value) to avoid direct assignment on
requested_algorithm variable.
- Avoid direct access of requested_algorithm to encapsulate
requested_algorithm variable

13 files changed, 143 insertions, 50 deletions

diff --git a/mysql-test/suite/innodb/r/alter_algorithm,INPLACE.rdiff b/mysql-test/suite/innodb/r/alter_algorithm,INPLACE.rdiff
index 805ccdb563c..a176a9af29e 100644
--- a/mysql-test/suite/innodb/r/alter_algorithm,INPLACE.rdiff
+++ b/mysql-test/suite/innodb/r/alter_algorithm,INPLACE.rdiff
@@ -1,6 +1,6 @@
---- alter_algorithm.result
-+++ alter_algorithm.reject
-@@ -7,40 +7,40 @@
+--- alter_algorithm.result	2020-04-30 21:39:48.923115511 +0530
++++ alter_algorithm.reject	2020-04-30 21:45:04.131642093 +0530
+@@ -7,43 +7,43 @@
  INSERT INTO t1(f1, f2, f3) VALUES(1, 1, 1);
  SELECT @@alter_algorithm;
  @@alter_algorithm
@@ -55,10 +55,15 @@
 -info: Records: 1  Duplicates: 0  Warnings: 0
 +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,
-@@ -53,22 +53,22 @@
+@@ -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);
  ALTER TABLE t1 ADD INDEX idx1(f4), page_compressed=1;
@@ -91,7 +96,7 @@
  DROP TABLE t2, t1;
  affected rows: 0
  CREATE TABLE t1(f1 INT NOT NULL,
-@@ -81,27 +81,27 @@
+@@ -84,28 +84,27 @@
  INSERT INTO t1(f1, f2) VALUES(1, 1);
  # Add column at the end of the table
  ALTER TABLE t1 ADD COLUMN f4 char(100) default 'BIG WALL';
@@ -119,7 +124,9 @@
 +info: Records: 0  Duplicates: 0  Warnings: 0
  # Rename table
  ALTER TABLE t1 RENAME t3;
- affected rows: 0
+-affected rows: 1
+-info: Records: 1  Duplicates: 0  Warnings: 0
++affected rows: 0
  # Drop Virtual Column
  ALTER TABLE t3 DROP COLUMN vcol;
 -affected rows: 1
@@ -129,7 +136,7 @@
  # Column length varies
  ALTER TABLE t2 CHANGE f3 f3 VARCHAR(20);
  affected rows: 0
-@@ -109,12 +109,12 @@
+@@ -113,12 +112,12 @@
  SET foreign_key_checks = 0;
  affected rows: 0
  ALTER TABLE t3 ADD FOREIGN KEY fidx(f2) REFERENCES t2(f1);
diff --git a/mysql-test/suite/innodb/r/alter_algorithm,INSTANT.rdiff b/mysql-test/suite/innodb/r/alter_algorithm,INSTANT.rdiff
index 6d2ee160e46..414b7dc8b0c 100644
--- a/mysql-test/suite/innodb/r/alter_algorithm,INSTANT.rdiff
+++ b/mysql-test/suite/innodb/r/alter_algorithm,INSTANT.rdiff
@@ -1,6 +1,6 @@
---- alter_algorithm.result
-+++ alter_algorithm.reject
-@@ -7,40 +7,32 @@
+--- alter_algorithm.result	2020-04-30 21:39:48.923115511 +0530
++++ alter_algorithm.reject	2020-04-30 21:47:08.245465018 +0530
+@@ -7,43 +7,35 @@
  INSERT INTO t1(f1, f2, f3) VALUES(1, 1, 1);
  SELECT @@alter_algorithm;
  @@alter_algorithm
@@ -47,10 +47,15 @@
 -affected rows: 1
 -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,
-@@ -53,22 +45,17 @@
+@@ -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);
  ALTER TABLE t1 ADD INDEX idx1(f4), page_compressed=1;
@@ -78,7 +83,7 @@
  DROP TABLE t2, t1;
  affected rows: 0
  CREATE TABLE t1(f1 INT NOT NULL,
-@@ -81,27 +68,27 @@
+@@ -84,28 +71,27 @@
  INSERT INTO t1(f1, f2) VALUES(1, 1);
  # Add column at the end of the table
  ALTER TABLE t1 ADD COLUMN f4 char(100) default 'BIG WALL';
@@ -106,7 +111,9 @@
 +info: Records: 0  Duplicates: 0  Warnings: 0
  # Rename table
  ALTER TABLE t1 RENAME t3;
- affected rows: 0
+-affected rows: 1
+-info: Records: 1  Duplicates: 0  Warnings: 0
++affected rows: 0
  # Drop Virtual Column
  ALTER TABLE t3 DROP COLUMN vcol;
 -affected rows: 1
@@ -116,7 +123,7 @@
  # Column length varies
  ALTER TABLE t2 CHANGE f3 f3 VARCHAR(20);
  affected rows: 0
-@@ -109,12 +96,12 @@
+@@ -113,12 +99,12 @@
  SET foreign_key_checks = 0;
  affected rows: 0
  ALTER TABLE t3 ADD FOREIGN KEY fidx(f2) REFERENCES t2(f1);
diff --git a/mysql-test/suite/innodb/r/alter_algorithm,NOCOPY.rdiff b/mysql-test/suite/innodb/r/alter_algorithm,NOCOPY.rdiff
index c6ce83b5d9f..2aa8c72265a 100644
--- a/mysql-test/suite/innodb/r/alter_algorithm,NOCOPY.rdiff
+++ b/mysql-test/suite/innodb/r/alter_algorithm,NOCOPY.rdiff
@@ -1,6 +1,6 @@
---- alter_algorithm.result
-+++ alter_algorithm.reject
-@@ -7,40 +7,32 @@
+--- alter_algorithm.result	2020-04-30 21:39:48.923115511 +0530
++++ alter_algorithm.reject	2020-04-30 21:52:10.785967739 +0530
+@@ -7,43 +7,35 @@
  INSERT INTO t1(f1, f2, f3) VALUES(1, 1, 1);
  SELECT @@alter_algorithm;
  @@alter_algorithm
@@ -47,10 +47,15 @@
 -affected rows: 1
 -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,
-@@ -53,22 +45,22 @@
+@@ -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);
  ALTER TABLE t1 ADD INDEX idx1(f4), page_compressed=1;
@@ -83,7 +88,7 @@
  DROP TABLE t2, t1;
  affected rows: 0
  CREATE TABLE t1(f1 INT NOT NULL,
-@@ -81,27 +73,27 @@
+@@ -84,28 +76,27 @@
  INSERT INTO t1(f1, f2) VALUES(1, 1);
  # Add column at the end of the table
  ALTER TABLE t1 ADD COLUMN f4 char(100) default 'BIG WALL';
@@ -111,7 +116,9 @@
 +info: Records: 0  Duplicates: 0  Warnings: 0
  # Rename table
  ALTER TABLE t1 RENAME t3;
- affected rows: 0
+-affected rows: 1
+-info: Records: 1  Duplicates: 0  Warnings: 0
++affected rows: 0
  # Drop Virtual Column
  ALTER TABLE t3 DROP COLUMN vcol;
 -affected rows: 1
@@ -121,7 +128,7 @@
  # Column length varies
  ALTER TABLE t2 CHANGE f3 f3 VARCHAR(20);
  affected rows: 0
-@@ -109,12 +101,12 @@
+@@ -113,12 +104,12 @@
  SET foreign_key_checks = 0;
  affected rows: 0
  ALTER TABLE t3 ADD FOREIGN KEY fidx(f2) REFERENCES t2(f1);
diff --git a/mysql-test/suite/innodb/r/alter_algorithm.result b/mysql-test/suite/innodb/r/alter_algorithm.result
index bcfbe3355f9..717d31de6a0 100644
--- a/mysql-test/suite/innodb/r/alter_algorithm.result
+++ b/mysql-test/suite/innodb/r/alter_algorithm.result
@@ -41,6 +41,9 @@ info: Records: 1  Duplicates: 0  Warnings: 0
 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
 DROP TABLE t1;
 affected rows: 0
 CREATE TABLE t1(f1 INT PRIMARY KEY, f2 INT NOT NULL,
@@ -97,7 +100,8 @@ affected rows: 1
 info: Records: 1  Duplicates: 0  Warnings: 0
 # Rename table
 ALTER TABLE t1 RENAME t3;
-affected rows: 0
+affected rows: 1
+info: Records: 1  Duplicates: 0  Warnings: 0
 # Drop Virtual Column
 ALTER TABLE t3 DROP COLUMN vcol;
 affected rows: 1
diff --git a/mysql-test/suite/innodb/r/alter_algorithm2.result b/mysql-test/suite/innodb/r/alter_algorithm2.result
index 1cea3f4cd43..350c1c51482 100644
--- a/mysql-test/suite/innodb/r/alter_algorithm2.result
+++ b/mysql-test/suite/innodb/r/alter_algorithm2.result
@@ -54,3 +54,23 @@ DROP PROCEDURE p1;
 affected rows: 0
 DROP PROCEDURE p2;
 affected rows: 0
+CREATE TABLE t1(id INT PRIMARY KEY,
+col1 INT UNSIGNED NOT NULL UNIQUE)ENGINE=InnoDB;
+affected rows: 0
+INSERT INTO t1 VALUES(1,1),(2,2),(3,3);
+affected rows: 3
+info: Records: 3  Duplicates: 0  Warnings: 0
+SET ALTER_ALGORITHM=INSTANT;
+affected rows: 0
+ALTER TABLE t1 DROP COLUMN col1;
+ERROR 0A000: ALGORITHM=INSTANT is not supported for this operation. Try ALGORITHM=INPLACE
+ALTER TABLE t1 DROP COLUMN col1, ALGORITHM=NOCOPY;
+ERROR 0A000: ALGORITHM=NOCOPY is not supported for this operation. Try ALGORITHM=INPLACE
+ALTER TABLE t1 DROP COLUMN col1, ALGORITHM=DEFAULT;
+affected rows: 0
+info: Records: 0  Duplicates: 0  Warnings: 0
+ALTER TABLE t1 DROP PRIMARY KEY, ALGORITHM=DEFAULT;
+affected rows: 3
+info: Records: 3  Duplicates: 0  Warnings: 0
+DROP TABLE t1;
+affected rows: 0
diff --git a/mysql-test/suite/innodb/t/alter_algorithm.test b/mysql-test/suite/innodb/t/alter_algorithm.test
index d410a15154d..08c23b505f3 100644
--- a/mysql-test/suite/innodb/t/alter_algorithm.test
+++ b/mysql-test/suite/innodb/t/alter_algorithm.test
@@ -55,6 +55,10 @@ ALTER TABLE t1 ROW_FORMAT=COMPRESSED;
 --error $error_code
 ALTER TABLE t1 ENGINE=INNODB;
 
+# Irrespective of alter_algorithm value, the following command
+# should succeed because of explicitly mentioning ALGORTHM=DEFAULT
+ALTER TABLE t1 FORCE, ALGORITHM=DEFAULT;
+
 DROP TABLE t1;
 --disable_info
 
diff --git a/mysql-test/suite/innodb/t/alter_algorithm2.test b/mysql-test/suite/innodb/t/alter_algorithm2.test
index 02b49c797bc..cf538e30196 100644
--- a/mysql-test/suite/innodb/t/alter_algorithm2.test
+++ b/mysql-test/suite/innodb/t/alter_algorithm2.test
@@ -44,4 +44,16 @@ call p1();
 DROP TABLE t1;
 DROP PROCEDURE p1;
 DROP PROCEDURE p2;
+
+CREATE TABLE t1(id INT PRIMARY KEY,
+	        col1 INT UNSIGNED NOT NULL UNIQUE)ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1,1),(2,2),(3,3);
+SET ALTER_ALGORITHM=INSTANT;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED
+ALTER TABLE t1 DROP COLUMN col1;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED
+ALTER TABLE t1 DROP COLUMN col1, ALGORITHM=NOCOPY;
+ALTER TABLE t1 DROP COLUMN col1, ALGORITHM=DEFAULT;
+ALTER TABLE t1 DROP PRIMARY KEY, ALGORITHM=DEFAULT;
+DROP TABLE t1;
 --disable_info
diff --git a/sql/sql_alter.cc b/sql/sql_alter.cc
index b3a036eda9e..a68dcb31a4c 100644
--- a/sql/sql_alter.cc
+++ b/sql/sql_alter.cc
@@ -69,6 +69,10 @@ bool Alter_info::set_requested_algorithm(const LEX_CSTRING *str)
   return false;
 }
 
+void Alter_info::set_requested_algorithm(enum_alter_table_algorithm algo_val)
+{
+  requested_algorithm= algo_val;
+}
 
 bool Alter_info::set_requested_lock(const LEX_CSTRING *str)
 {
@@ -86,13 +90,16 @@ bool Alter_info::set_requested_lock(const LEX_CSTRING *str)
   return false;
 }
 
-const char* Alter_info::algorithm() const
+const char* Alter_info::algorithm_clause(THD *thd) const
 {
-  switch (requested_algorithm) {
+  switch (algorithm(thd)) {
   case ALTER_TABLE_ALGORITHM_INPLACE:
     return "ALGORITHM=INPLACE";
   case ALTER_TABLE_ALGORITHM_COPY:
     return "ALGORITHM=COPY";
+  case ALTER_TABLE_ALGORITHM_NONE:
+    DBUG_ASSERT(0);
+    /* Fall through */
   case ALTER_TABLE_ALGORITHM_DEFAULT:
     return "ALGORITHM=DEFAULT";
   case ALTER_TABLE_ALGORITHM_NOCOPY:
@@ -123,9 +130,6 @@ const char* Alter_info::lock() const
 bool Alter_info::supports_algorithm(THD *thd, enum_alter_inplace_result result,
                                     const Alter_inplace_info *ha_alter_info)
 {
-  if (requested_algorithm == Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT)
-    requested_algorithm = (Alter_info::enum_alter_table_algorithm) thd->variables.alter_algorithm;
-
   switch (result) {
   case HA_ALTER_INPLACE_EXCLUSIVE_LOCK:
   case HA_ALTER_INPLACE_SHARED_LOCK:
@@ -134,16 +138,16 @@ bool Alter_info::supports_algorithm(THD *thd, enum_alter_inplace_result result,
      return false;
   case HA_ALTER_INPLACE_COPY_NO_LOCK:
   case HA_ALTER_INPLACE_COPY_LOCK:
-    if (requested_algorithm >= Alter_info::ALTER_TABLE_ALGORITHM_NOCOPY)
+    if (algorithm(thd) >= Alter_info::ALTER_TABLE_ALGORITHM_NOCOPY)
     {
-      ha_alter_info->report_unsupported_error(algorithm(),
+      ha_alter_info->report_unsupported_error(algorithm_clause(thd),
                                               "ALGORITHM=INPLACE");
       return true;
     }
     return false;
   case HA_ALTER_INPLACE_NOCOPY_NO_LOCK:
   case HA_ALTER_INPLACE_NOCOPY_LOCK:
-    if (requested_algorithm == Alter_info::ALTER_TABLE_ALGORITHM_INSTANT)
+    if (algorithm(thd) == Alter_info::ALTER_TABLE_ALGORITHM_INSTANT)
     {
       ha_alter_info->report_unsupported_error("ALGORITHM=INSTANT",
                                               "ALGORITHM=NOCOPY");
@@ -151,9 +155,9 @@ bool Alter_info::supports_algorithm(THD *thd, enum_alter_inplace_result result,
     }
     return false;
   case HA_ALTER_INPLACE_NOT_SUPPORTED:
-    if (requested_algorithm >= Alter_info::ALTER_TABLE_ALGORITHM_INPLACE)
+    if (algorithm(thd) >= Alter_info::ALTER_TABLE_ALGORITHM_INPLACE)
     {
-      ha_alter_info->report_unsupported_error(algorithm(),
+      ha_alter_info->report_unsupported_error(algorithm_clause(thd),
 					      "ALGORITHM=COPY");
       return true;
     }
@@ -174,7 +178,7 @@ bool Alter_info::supports_lock(THD *thd, enum_alter_inplace_result result,
   case HA_ALTER_INPLACE_EXCLUSIVE_LOCK:
     // If SHARED lock and no particular algorithm was requested, use COPY.
     if (requested_lock == Alter_info::ALTER_TABLE_LOCK_SHARED &&
-        requested_algorithm == Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT &&
+        algorithm(thd) == Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT &&
         thd->variables.alter_algorithm ==
                 Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT)
          return false;
@@ -237,6 +241,14 @@ bool Alter_info::vers_prohibited(THD *thd) const
   return false;
 }
 
+Alter_info::enum_alter_table_algorithm
+Alter_info::algorithm(const THD *thd) const
+{
+  if (requested_algorithm == ALTER_TABLE_ALGORITHM_NONE)
+   return (Alter_info::enum_alter_table_algorithm) thd->variables.alter_algorithm;
+  return requested_algorithm;
+}
+
 
 Alter_table_ctx::Alter_table_ctx()
   : datetime_field(NULL), error_if_not_empty(false),
diff --git a/sql/sql_alter.h b/sql/sql_alter.h
index 10aafe1ab37..53d0c8438f8 100644
--- a/sql/sql_alter.h
+++ b/sql/sql_alter.h
@@ -57,7 +57,10 @@ public:
     ALTER_TABLE_ALGORITHM_NOCOPY,
 
     // Instant should allow any operation that changes metadata only.
-    ALTER_TABLE_ALGORITHM_INSTANT
+    ALTER_TABLE_ALGORITHM_INSTANT,
+
+    // When there is no specification of algorithm during alter table.
+    ALTER_TABLE_ALGORITHM_NONE
   };
 
 
@@ -104,8 +107,11 @@ public:
   List<const char>              partition_names;
   // Number of partitions.
   uint                          num_parts;
+private:
   // Type of ALTER TABLE algorithm.
   enum_alter_table_algorithm    requested_algorithm;
+
+public:
   // Type of ALTER TABLE lock.
   enum_alter_table_lock         requested_lock;
 
@@ -114,7 +120,7 @@ public:
   flags(0), partition_flags(0),
     keys_onoff(LEAVE_AS_IS),
     num_parts(0),
-    requested_algorithm(ALTER_TABLE_ALGORITHM_DEFAULT),
+    requested_algorithm(ALTER_TABLE_ALGORITHM_NONE),
     requested_lock(ALTER_TABLE_LOCK_DEFAULT)
   {}
 
@@ -130,7 +136,7 @@ public:
     keys_onoff= LEAVE_AS_IS;
     num_parts= 0;
     partition_names.empty();
-    requested_algorithm= ALTER_TABLE_ALGORITHM_DEFAULT;
+    requested_algorithm= ALTER_TABLE_ALGORITHM_NONE;
     requested_lock= ALTER_TABLE_LOCK_DEFAULT;
   }
 
@@ -178,9 +184,15 @@ public:
   bool set_requested_lock(const LEX_CSTRING *str);
 
   /**
+    Set the requested algorithm to the given algorithm value
+    @param algo_value	algorithm to be set
+   */
+  void set_requested_algorithm(enum_alter_table_algorithm algo_value);
+
+  /**
      Returns the algorithm value in the format "algorithm=value"
   */
-  const char* algorithm() const;
+  const char* algorithm_clause(THD *thd) const;
 
   /**
      Returns the lock value in the format "lock=value"
@@ -216,6 +228,12 @@ public:
   bool supports_lock(THD *thd, enum_alter_inplace_result result,
                      const Alter_inplace_info *ha_alter_info);
 
+  /**
+    Return user requested algorithm. If user does not specify
+    algorithm then return alter_algorithm variable value.
+   */
+  enum_alter_table_algorithm algorithm(const THD *thd) const;
+
 private:
   Alter_info &operator=(const Alter_info &rhs); // not implemented
   Alter_info(const Alter_info &rhs);            // not implemented
diff --git a/sql/sql_partition.cc b/sql/sql_partition.cc
index 5fdca153ef7..c557f438b41 100644
--- a/sql/sql_partition.cc
+++ b/sql/sql_partition.cc
@@ -6008,7 +6008,7 @@ the generated partition syntax in a correct manner.
         */
         if (alter_info->partition_flags != ALTER_PARTITION_INFO ||
             !table->part_info ||
-            alter_info->requested_algorithm !=
+            alter_info->algorithm(thd) !=
               Alter_info::ALTER_TABLE_ALGORITHM_INPLACE ||
             !table->part_info->has_same_partitioning(part_info))
         {
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index ed1c3c401d3..e2a8cafe784 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -9558,7 +9558,7 @@ do_continue:;
   */
   if (!(alter_info->flags & ~(ALTER_RENAME | ALTER_KEYS_ONOFF)) &&
       alter_info->partition_flags == 0 &&
-      alter_info->requested_algorithm !=
+      alter_info->algorithm(thd) !=
       Alter_info::ALTER_TABLE_ALGORITHM_COPY)   // No need to touch frm.
   {
     bool res;
@@ -9636,7 +9636,7 @@ do_continue:;
                "LOCK=DEFAULT");
       DBUG_RETURN(true);
     }
-    else if (alter_info->requested_algorithm !=
+    else if (alter_info->algorithm(thd) !=
              Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT)
     {
       my_error(ER_ALTER_OPERATION_NOT_SUPPORTED_REASON, MYF(0),
@@ -9676,20 +9676,21 @@ do_continue:;
       using in-place API.
   */
   if ((thd->variables.alter_algorithm == Alter_info::ALTER_TABLE_ALGORITHM_COPY &&
-       alter_info->requested_algorithm !=
+       alter_info->algorithm(thd) !=
        Alter_info::ALTER_TABLE_ALGORITHM_INPLACE)
       || is_inplace_alter_impossible(table, create_info, alter_info)
       || IF_PARTITIONING((partition_changed &&
           !(table->s->db_type()->partition_flags() & HA_USE_AUTO_PARTITION)), 0))
   {
-    if (alter_info->requested_algorithm ==
+    if (alter_info->algorithm(thd) ==
         Alter_info::ALTER_TABLE_ALGORITHM_INPLACE)
     {
       my_error(ER_ALTER_OPERATION_NOT_SUPPORTED, MYF(0),
                "ALGORITHM=INPLACE", "ALGORITHM=COPY");
       DBUG_RETURN(true);
     }
-    alter_info->requested_algorithm= Alter_info::ALTER_TABLE_ALGORITHM_COPY;
+    alter_info->set_requested_algorithm(
+      Alter_info::ALTER_TABLE_ALGORITHM_COPY);
   }
 
   /*
@@ -9809,7 +9810,7 @@ do_continue:;
   /* Remember that we have not created table in storage engine yet. */
   bool no_ha_table= true;
 
-  if (alter_info->requested_algorithm != Alter_info::ALTER_TABLE_ALGORITHM_COPY)
+  if (alter_info->algorithm(thd) != Alter_info::ALTER_TABLE_ALGORITHM_COPY)
   {
     Alter_inplace_info ha_alter_info(create_info, alter_info,
                                      key_info, key_count,
@@ -9900,7 +9901,7 @@ do_continue:;
     // If SHARED lock and no particular algorithm was requested, use COPY.
     if (inplace_supported == HA_ALTER_INPLACE_EXCLUSIVE_LOCK &&
         alter_info->requested_lock == Alter_info::ALTER_TABLE_LOCK_SHARED &&
-         alter_info->requested_algorithm ==
+         alter_info->algorithm(thd) ==
                  Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT &&
          thd->variables.alter_algorithm ==
                  Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT)
@@ -10743,7 +10744,8 @@ bool mysql_recreate_table(THD *thd, TABLE_LIST *table_list, bool table_copy)
   alter_info.flags= (ALTER_CHANGE_COLUMN | ALTER_RECREATE);
 
   if (table_copy)
-    alter_info.requested_algorithm= Alter_info::ALTER_TABLE_ALGORITHM_COPY;
+    alter_info.set_requested_algorithm(
+      Alter_info::ALTER_TABLE_ALGORITHM_COPY);
 
   bool res= mysql_alter_table(thd, &null_clex_str, &null_clex_str, &create_info,
                                 table_list, &alter_info, 0,
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 2a382dc7666..14d71139dad 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -8531,8 +8531,8 @@ opt_index_lock_algorithm:
 alter_algorithm_option:
           ALGORITHM_SYM opt_equal DEFAULT
           {
-            Lex->alter_info.requested_algorithm=
-              Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT;
+            Lex->alter_info.set_requested_algorithm(
+              Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT);
           }
         | ALGORITHM_SYM opt_equal ident
           {
diff --git a/sql/sql_yacc_ora.yy b/sql/sql_yacc_ora.yy
index c8620543d08..d174e02fc24 100644
--- a/sql/sql_yacc_ora.yy
+++ b/sql/sql_yacc_ora.yy
@@ -8468,8 +8468,8 @@ opt_index_lock_algorithm:
 alter_algorithm_option:
           ALGORITHM_SYM opt_equal DEFAULT
           {
-            Lex->alter_info.requested_algorithm=
-              Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT;
+            Lex->alter_info.set_requested_algorithm(
+              Alter_info::ALTER_TABLE_ALGORITHM_DEFAULT);
           }
         | ALGORITHM_SYM opt_equal ident
           {