Merge a contribution from Ryan Mack at Facebook:

Bugfix for 53290, fast unique index creation fails on duplicate null values

    Summary:
    Bug in the fast index creation code incorrectly considers null
    values to be duplicates during block merging.  Innodb policy is that
    multiple null values are allowed in a unique index.  Null duplicates
    were correctly ignored while sorting individual blocks and with slow
    index creation.

    Test Plan:
    mtr, including new test, load dbs using deferred index creation

    DiffCamp Revision: 110840
    Reviewed By: mcallaghan
    CC: mcallaghan, mysql-devel@lists
    Revert Plan:
    OK

mysql-test/suite/innodb_plugin/r/innodb_bug53290.result

+create table bug53290 (x bigint) engine=innodb;
+insert into bug53290 () values (),(),(),(),(),(),(),(),(),(),(),();
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+alter table bug53290 add unique index `idx` (x);
+drop table bug53290;

mysql-test/suite/innodb_plugin/t/innodb_bug53290.test

+-- source include/have_innodb_plugin.inc
+
+create table bug53290 (x bigint) engine=innodb;
+
+insert into bug53290 () values (),(),(),(),(),(),(),(),(),(),(),();
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+insert into bug53290 select * from bug53290;
+
+alter table bug53290 add unique index `idx` (x);
+
+drop table bug53290;

storage/innodb_plugin/include/rem0cmp.h

@@ -148,7 +148,9 @@ cmp_rec_rec_simple(
 	const rec_t*		rec2,	/*!< in: physical record */
 	const ulint*		offsets1,/*!< in: rec_get_offsets(rec1, ...) */
 	const ulint*		offsets2,/*!< in: rec_get_offsets(rec2, ...) */
-	const dict_index_t*	index);	/*!< in: data dictionary index */
+	const dict_index_t*	index,	/*!< in: data dictionary index */
+	ibool*			null_eq);/*!< out: set to TRUE if
+					found matching null values */
 /*************************************************************//**
 This function is used to compare two physical records. Only the common
 first fields are compared, and if an externally stored field is

storage/innodb_plugin/rem/rem0cmp.c

@@ -706,7 +706,9 @@ cmp_rec_rec_simple(
 	const rec_t*		rec2,	/*!< in: physical record */
 	const ulint*		offsets1,/*!< in: rec_get_offsets(rec1, ...) */
 	const ulint*		offsets2,/*!< in: rec_get_offsets(rec2, ...) */
-	const dict_index_t*	index)	/*!< in: data dictionary index */
+	const dict_index_t*	index,	/*!< in: data dictionary index */
+	ibool*			null_eq)/*!< out: set to TRUE if
+					found matching null values */
 {
 	ulint		rec1_f_len;	/*!< length of current field in rec1 */
 	const byte*	rec1_b_ptr;	/*!< pointer to the current byte
@@ -753,6 +755,9 @@ cmp_rec_rec_simple(
 		    || rec2_f_len == UNIV_SQL_NULL) {
 
 			if (rec1_f_len == rec2_f_len) {
+				if (null_eq) {
+					*null_eq = TRUE;
+				}
 
 				goto next_field;
 

storage/innodb_plugin/row/row0merge.c

@@ -1075,11 +1075,14 @@ row_merge_cmp(
 						record to be compared */
 	const ulint*		offsets1,	/*!< in: first record offsets */
 	const ulint*		offsets2,	/*!< in: second record offsets */
-	const dict_index_t*	index)		/*!< in: index */
+	const dict_index_t*	index,		/*!< in: index */
+	ibool*			null_eq)	/*!< out: set to TRUE if
+						found matching null values */
 {
 	int	cmp;
 
-	cmp = cmp_rec_rec_simple(mrec1, mrec2, offsets1, offsets2, index);
+	cmp = cmp_rec_rec_simple(mrec1, mrec2, offsets1, offsets2, index,
+				 null_eq);
 
 #ifdef UNIV_DEBUG
 	if (row_merge_print_cmp) {
@@ -1445,11 +1448,13 @@ row_merge_blocks(
 	}
 
 	while (mrec0 && mrec1) {
+		ibool	null_eq = FALSE;
 		switch (row_merge_cmp(mrec0, mrec1,
-				      offsets0, offsets1, index)) {
+				      offsets0, offsets1, index,
+				      &null_eq)) {
 		case 0:
 			if (UNIV_UNLIKELY
-			    (dict_index_is_unique(index))) {
+			    (dict_index_is_unique(index) && !null_eq)) {
 				innobase_rec_to_mysql(table, mrec0,
 						      index, offsets0);
 				mem_heap_free(heap);