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

1 files changed, 22 insertions, 4 deletions

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