MDEV-37296 ALTER TABLE allows adding unique hash key with duplicate values

Problem:
=======
- During copy algorithm, InnoDB fails to detect the duplicate
key error for unique hash key blob index. Unique HASH index
treated as virtual index inside InnoDB.
When table does unique hash key , server does search on
the hash key before doing any insert operation and
finds the duplicate value in check_duplicate_long_entry_key().
Bulk insert does all the insert together when copy of
intermediate table is finished. This leads to undetection of
duplicate key error while building the index.

Solution:
========
- Avoid bulk insert operation when table does have unique
hash key blob index.

dict_table_t::can_bulk_insert(): To check whether the table
is eligible for bulk insert operation during alter copy algorithm.
Check whether any virtual column name starts with DB_ROW_HASH_ to
know whether blob column has unique index on it.

Author: Thirunarayanan

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

@@ -112,3 +112,25 @@ SET innodb_lock_wait_timeout=default;
 DROP TABLE t1;
 DROP TABLE IF EXISTS t2;
 # restart
+#
+#  MDEV-37296 ALTER TABLE allows adding unique hash key
+#		with duplicate values
+#
+CREATE TABLE t (pk INT PRIMARY KEY, a INT, b TEXT) ENGINE=InnoDB;
+INSERT INTO t VALUES (5,3,'foo'), (1,NULL,'bar'), (3,3,'foo');
+ALTER TABLE t ADD UNIQUE (a,b);
+ERROR 23000: Duplicate entry '3-foo' for key 'a'
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `pk` int(11) NOT NULL,
+  `a` int(11) DEFAULT NULL,
+  `b` text DEFAULT NULL,
+  PRIMARY KEY (`pk`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+SELECT * FROM t;
+pk	a	b
+1	NULL	bar
+3	3	foo
+5	3	foo
+DROP TABLE t;

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

@@ -130,3 +130,15 @@ SET innodb_lock_wait_timeout=default;
 DROP TABLE t1;
 DROP TABLE IF EXISTS t2;
 --source include/restart_mysqld.inc
+
+--echo #
+--echo #  MDEV-37296 ALTER TABLE allows adding unique hash key
+--echo #		with duplicate values
+--echo #
+CREATE TABLE t (pk INT PRIMARY KEY, a INT, b TEXT) ENGINE=InnoDB;
+INSERT INTO t VALUES (5,3,'foo'), (1,NULL,'bar'), (3,3,'foo');
+--error ER_DUP_ENTRY
+ALTER TABLE t ADD UNIQUE (a,b);
+SHOW CREATE TABLE t;
+SELECT * FROM t;
+DROP TABLE t;

storage/innobase/include/dict0mem.h

@@ -2171,6 +2171,11 @@ struct dict_table_t {
                       (as part of rolling back TRUNCATE) */
   dberr_t rename_tablespace(span<const char> new_name, bool replace) const;
 
+  /** Whether the table is eligible to do bulk insert operation
+  @param trx transaction which tries to do bulk insert
+  @retval true if table can do bulk insert
+  @retval false otherwise */
+  bool can_bulk_insert(const trx_t &trx) const noexcept;
 private:
 	/** Initialize instant->field_map.
 	@param[in]	table	table definition to copy from */

storage/innobase/row/row0ins.cc

@@ -2619,6 +2619,21 @@ static uint64_t row_parse_int(const byte *data, size_t len,
   return 0;
 }
 
+inline bool dict_table_t::can_bulk_insert(const trx_t &trx) const noexcept
+{
+  if (is_temporary() || versioned() || has_spatial_index())
+    return false;
+  /* Bulk insert is not compatible with HA_CHECK_UNIQUE_AFTER_WRITE.
+  Refuse bulk insert if HA_KEY_ALG_LONG_HASH indexes exist.
+  handler::ha_check_long_uniques() assumes that all data
+  passed to ha_innobase::write_row() is available immediately. */
+  if (const char *s= v_col_names)
+    for (auto n= n_v_cols; n--; s+= strlen(s) + 1)
+      if (!strncmp(s, C_STRING_WITH_LEN("DB_ROW_HASH_")))
+        return false; /* make_long_hash_field_name() */
+  return !trx.check_foreigns || (foreign_set.empty() && referenced_set.empty());
+}
+
 /***************************************************************//**
 Tries to insert an entry into a clustered index, ignoring foreign key
 constraints. If a record with the same unique key is found, the other
@@ -2824,12 +2839,7 @@ row_ins_clust_index_entry_low(
 		/* If foreign key exist and foreign key is enabled
 		then avoid using bulk insert for copy algorithm */
 		if (innodb_alter_copy_bulk
-		    && !index->table->is_temporary()
-		    && !index->table->versioned()
-		    && !index->table->has_spatial_index()
-		    && (!trx->check_foreigns
-                        || (index->table->foreign_set.empty()
-                            && index->table->referenced_set.empty()))) {
+		    && index->table->can_bulk_insert(*trx)) {
 			ut_ad(page_is_empty(block->page.frame));
 			/* This code path has been executed at the
 			start of the alter operation. Consecutive