MDEV-34813 A simple implementation of ha_partition::compare_key_parts

It is not clear that the three Compare_key enums form a hierarchy like
alter algorithms do. So on the safe side (in case MDEV-22168 gets
implemented without looking at this code) we should return NotEqual if
partition engines do not return the same enum value. There's a static
merge function that merges these enums, but it is used to merge the
Compare_keys of different key parts (horizontally), rather than
different partitions (vertically).

mysql-test/suite/parts/r/alter_table.result

@@ -59,4 +59,18 @@ index_name	comment
 PRIMARY	
 i2	disabled
 drop table t1;
+#
+# MDEV-34813 ALGORITHM=INSTANT does not work for partitioned tables on indexed column
+#
+CREATE TABLE `t1` (
+`f1` datetime ,
+`f2` VARCHAR(2)  ,
+`f3` VARCHAR(200) ,
+`f4` VARCHAR(100)  ,
+INDEX `i3` (`f4`)  )
+PARTITION BY RANGE COLUMNS(`f2`)
+(PARTITION `p_01` VALUES LESS THAN ('02') ENGINE = InnoDB,
+PARTITION `p_31` VALUES LESS THAN (MAXVALUE) ENGINE = InnoDB);
+ALTER online TABLE t1 MODIFY COLUMN `f4`  VARCHAR(500) , ALGORITHM=INSTANT, LOCK=NONE;
+drop table t1;
 # End of 10.5 tests

mysql-test/suite/parts/t/alter_table.test

@@ -52,4 +52,23 @@ alter table t1 add partition (partition p4);
 select index_name, comment from information_schema.statistics where table_schema='test' and table_name='t1';
 drop table t1;
 
+--echo #
+--echo # MDEV-34813 ALGORITHM=INSTANT does not work for partitioned tables on indexed column
+--echo #
+
+--source include/have_innodb.inc
+CREATE TABLE `t1` (
+    `f1` datetime ,
+    `f2` VARCHAR(2)  ,
+    `f3` VARCHAR(200) ,
+    `f4` VARCHAR(100)  ,
+    INDEX `i3` (`f4`)  )
+    PARTITION BY RANGE COLUMNS(`f2`)
+    (PARTITION `p_01` VALUES LESS THAN ('02') ENGINE = InnoDB,
+     PARTITION `p_31` VALUES LESS THAN (MAXVALUE) ENGINE = InnoDB);
+
+ALTER online TABLE t1 MODIFY COLUMN `f4`  VARCHAR(500) , ALGORITHM=INSTANT, LOCK=NONE;
+
+drop table t1;
+
 --echo # End of 10.5 tests

sql/ha_partition.cc

@@ -3178,6 +3178,24 @@ err1:
   DBUG_RETURN(true);
 }
 
+Compare_keys ha_partition::compare_key_parts(
+  const Field &old_field,
+  const Column_definition &new_field,
+  const KEY_PART_INFO &old_part,
+  const KEY_PART_INFO &new_part) const
+{
+  Compare_keys res= m_file[0]->compare_key_parts(old_field, new_field,
+                                                 old_part, new_part);
+  /*
+    Partitions have the same storage engine (until MDEV-22168) so the
+    calls should all return the same value for now.
+  */
+  for (uint i= 1; i < m_tot_parts; i++)
+    if (res != m_file[i]->compare_key_parts(old_field, new_field,
+                                            old_part, new_part))
+      return Compare_keys::NotEqual;
+  return res;
+}
 
 /**
   Setup m_engine_array

sql/ha_partition.h

@@ -481,6 +481,11 @@ public:
      m_part_info= part_info;
      m_is_sub_partitioned= part_info->is_sub_partitioned();
   }
+  Compare_keys compare_key_parts(
+    const Field &old_field,
+    const Column_definition &new_field,
+    const KEY_PART_INFO &old_part,
+    const KEY_PART_INFO &new_part) const override;
 
   void return_record_by_parent() override;