Bug #14049391 INNODB MISCALCULATES AUTO-INCREMENT AFTER DECREASING

                        AUTO_INCREMENT_INCREMENT
Problem:
=======
When auto_increment_increment system variable decreases,
immediate next value of auto increment column is not affected.

Solution:
========
	Get the previous inserted value of auto increment column by
subtracting the previous auto_increment_increment from next
auto increment value. After that calculate the current autoinc value
using newly changed auto_increment_increment variable.

	Approved by Sunny [rb#4394]

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

@@ -1357,3 +1357,30 @@ t1	CREATE TABLE `t1` (
 INSERT INTO t1 VALUES ();
 ERROR HY000: Failed to read auto-increment value from storage engine
 DROP TABLE t1;
+#
+# Bug #14049391	 INNODB MISCALCULATES AUTO-INCREMENT
+#	AFTER CHANGING AUTO_INCREMENT_INCREMEMENT
+#
+CREATE TABLE t ( i INT AUTO_INCREMENT, KEY(i) ) ENGINE=InnoDB;
+SET auto_increment_increment = 300;
+INSERT INTO t VALUES (NULL), (NULL);
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `i` int(11) NOT NULL AUTO_INCREMENT,
+  KEY `i` (`i`)
+) ENGINE=InnoDB AUTO_INCREMENT=601 DEFAULT CHARSET=latin1
+SET auto_increment_increment = 50;
+INSERT INTO t VALUES (NULL);
+SELECT * FROM t;
+i
+1
+301
+351
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `i` int(11) NOT NULL AUTO_INCREMENT,
+  KEY `i` (`i`)
+) ENGINE=InnoDB AUTO_INCREMENT=401 DEFAULT CHARSET=latin1
+DROP TABLE t;

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

@@ -685,3 +685,17 @@ SHOW CREATE TABLE t1;
 --error 1467
 INSERT INTO t1 VALUES ();
 DROP TABLE t1;
+
+--echo #
+--echo # Bug #14049391	 INNODB MISCALCULATES AUTO-INCREMENT
+--echo #	AFTER CHANGING AUTO_INCREMENT_INCREMEMENT
+--echo #
+CREATE TABLE t ( i INT AUTO_INCREMENT, KEY(i) ) ENGINE=InnoDB;
+SET auto_increment_increment = 300;
+INSERT INTO t VALUES (NULL), (NULL);
+SHOW CREATE TABLE t;
+SET auto_increment_increment = 50;
+INSERT INTO t VALUES (NULL);
+SELECT * FROM t;
+SHOW CREATE TABLE t;
+DROP TABLE t;

storage/innobase/handler/ha_innodb.cc

@@ -10235,6 +10235,21 @@ ha_innobase::get_auto_increment(
 
 		current = *first_value > col_max_value ? autoinc : *first_value;
 
+		/* If the increment step of the auto increment column
+		decreases then it is not affecting the immediate
+		next value in the series. */
+		if (prebuilt->autoinc_increment > increment) {
+
+			current = autoinc - prebuilt->autoinc_increment;
+
+			current = innobase_next_autoinc(
+				current, 1, increment, 1, col_max_value);
+
+			dict_table_autoinc_initialize(prebuilt->table, current);
+
+			*first_value = current;
+		}
+
 		/* Compute the last value in the interval */
 		next_value = innobase_next_autoinc(
 			current, *nb_reserved_values, increment, offset,