MDEV-23805 Make Online DDL to Instant DDL when table is empty

Thirunarayanan · Thirunarayanan · commit d270525dfde8 · 2021-11-12T17:46:35.000+05:30
- In ha_innobase::prepare_inplace_alter_table(), InnoDB should
check whether the table is empty. If the table is empty then
server should avoid downgrading the MDL after prepare phase.
It is more like instant alter, does change only in dicationary
and metadata.

- Changed few debug test case to make non-empty DDL table
diff --git a/mysql-test/suite/gcol/r/virtual_index_drop.result b/mysql-test/suite/gcol/r/virtual_index_drop.result
@@ -25,6 +25,7 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DROP TABLE t1;
 CREATE TABLE t1(f1 INT, f2 INT AS (f1) VIRTUAL)ENGINE=InnoDB;
+INSERT INTO t1(f1) VALUES(1);
 SET DEBUG_DBUG="+d,create_index_fail";
 SET DEBUG_SYNC="innodb_inplace_alter_table_enter SIGNAL con1_go WAIT_FOR alter_signal";
 ALTER TABLE t1 ADD COLUMN f3 INT AS (f1) VIRTUAL, ADD INDEX(f2, f3);
@@ -33,6 +34,7 @@ SET DEBUG_SYNC="now WAIT_FOR con1_go";
 BEGIN;
 SELECT * FROM t1;
 f1	f2
+1	1
 SET DEBUG_SYNC="now SIGNAL alter_signal";
 connection default;
 ERROR 23000: Duplicate entry '' for key '*UNKNOWN*'
@@ -47,6 +49,7 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DROP TABLE t1;
 CREATE TABLE t1(f1 INT, f2 INT AS (f1) VIRTUAL)ENGINE=InnoDB;
+INSERT INTO t1(f1) VALUES(1);
 SET DEBUG_DBUG="+d,create_index_fail";
 SET DEBUG_SYNC="innodb_inplace_alter_table_enter SIGNAL con1_go WAIT_FOR alter_signal";
 ALTER TABLE t1 ADD INDEX(f2);
diff --git a/mysql-test/suite/gcol/t/virtual_index_drop.test b/mysql-test/suite/gcol/t/virtual_index_drop.test
@@ -29,6 +29,7 @@ DROP TABLE t1;
 # new_vcol_info in index when rollback of alter happens
 
 CREATE TABLE t1(f1 INT, f2 INT AS (f1) VIRTUAL)ENGINE=InnoDB;
+INSERT INTO t1(f1) VALUES(1);
 SET DEBUG_DBUG="+d,create_index_fail";
 SET DEBUG_SYNC="innodb_inplace_alter_table_enter SIGNAL con1_go WAIT_FOR alter_signal";
 SEND ALTER TABLE t1 ADD COLUMN f3 INT AS (f1) VIRTUAL, ADD INDEX(f2, f3);
@@ -47,6 +48,7 @@ SHOW CREATE TABLE t1;
 DROP TABLE t1;
 
 CREATE TABLE t1(f1 INT, f2 INT AS (f1) VIRTUAL)ENGINE=InnoDB;
+INSERT INTO t1(f1) VALUES(1);
 SET DEBUG_DBUG="+d,create_index_fail";
 SET DEBUG_SYNC="innodb_inplace_alter_table_enter SIGNAL con1_go WAIT_FOR alter_signal";
 send ALTER TABLE t1 ADD INDEX(f2);
diff --git a/mysql-test/suite/innodb/r/alter_candidate_key.result b/mysql-test/suite/innodb/r/alter_candidate_key.result
@@ -34,6 +34,7 @@ CREATE TABLE t1(f1 INT, f2 INT,
 PRIMARY KEY(f1, f2),
 UNIQUE INDEX uidx2 (f1, f2),
 UNIQUE INDEX uidx1 (f2))ENGINE=InnoDB;
+INSERT INTO t1 VALUES(2, 2);
 ALTER TABLE t1 DROP PRIMARY KEY;
 SHOW CREATE TABLE t1;
 Table	Create Table
@@ -66,6 +67,7 @@ test.t1	check	status	OK
 DROP TABLE t1;
 SET SQL_MODE= strict_trans_tables;
 CREATE TABLE t1(a INT UNIQUE) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1);
 SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL dml WAIT_FOR dml_done';
 ALTER TABLE t1 MODIFY COLUMN a INT NOT NULL;
 connection con1;
diff --git a/mysql-test/suite/innodb/r/alter_not_null_debug.result b/mysql-test/suite/innodb/r/alter_not_null_debug.result
@@ -80,6 +80,7 @@ SET DEBUG_SYNC='RESET';
 #
 CREATE TABLE t1 (f VARCHAR(8) CHARACTER SET latin1 COLLATE latin1_swedish_ci)
 ENGINE=InnoDB;
+INSERT INTO t1 VALUES('ZERO');
 connection con1;
 SET DEBUG_SYNC = 'row_log_table_apply1_before SIGNAL scanned WAIT_FOR insert_done';
 ALTER TABLE t1 MODIFY f VARCHAR(256) COLLATE latin1_german2_ci NOT NULL;
@@ -96,5 +97,6 @@ ALTER TABLE t1 CHANGE f eins VARCHAR(257) COLLATE latin1_german1_ci NOT NULL,
 ALGORITHM=INSTANT;
 SELECT * FROM t1;
 eins
+ZERO
 one
 DROP TABLE t1;
diff --git a/mysql-test/suite/innodb/r/alter_primary_key.result b/mysql-test/suite/innodb/r/alter_primary_key.result
@@ -4,6 +4,7 @@
 #
 CREATE TABLE t0 (pk INT PRIMARY KEY) ENGINE=InnoDB;
 CREATE TABLE t1 (c CHAR(2) NOT NULL) ENGINE=InnoDB;
+INSERT INTO  t1 VALUES('cd');
 connect  con1,localhost,root,,;
 BEGIN;
 INSERT INTO t0 VALUES(1);
@@ -21,6 +22,7 @@ ERROR 23000: Duplicate entry 'a' for key 'PRIMARY'
 SET DEBUG_SYNC='RESET';
 SELECT * FROM t1;
 c
+cd
 ab
 ac
 DROP TABLE t0,t1;
diff --git a/mysql-test/suite/innodb/r/ddl_purge.result b/mysql-test/suite/innodb/r/ddl_purge.result
@@ -1,5 +1,6 @@
 CREATE TABLE t0 (pk INT PRIMARY KEY) ENGINE=InnoDB;
 CREATE TABLE t1 (pk INT PRIMARY KEY, b INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(100, 100);
 connect  con1,localhost,root,,test;
 BEGIN;
 INSERT INTO t0 SET pk=1;
diff --git a/mysql-test/suite/innodb/r/innodb-alter-tempfile.result b/mysql-test/suite/innodb/r/innodb-alter-tempfile.result
@@ -61,7 +61,7 @@ connect  con1,localhost,root,,;
 BEGIN;
 DELETE FROM mysql.innodb_table_stats;
 connect  con2,localhost,root,,;
-SET DEBUG_SYNC='inplace_after_index_build SIGNAL blocked WAIT_FOR ever';
+SET DEBUG_SYNC='innodb_inplace_alter_table_enter SIGNAL blocked WAIT_FOR ever';
 ALTER TABLE t1 FORCE;
 connection default;
 SET DEBUG_SYNC='now WAIT_FOR blocked';
diff --git a/mysql-test/suite/innodb/r/innodb-index-debug.result b/mysql-test/suite/innodb/r/innodb-index-debug.result
@@ -81,6 +81,7 @@ COUNT(k1)	k2	k3
 drop table t1;
 create table t1(k1 int auto_increment primary key,
 k2 char(200),k3 char(200))engine=innodb;
+INSERT INTO t1 VALUES(1, "test", "test");
 SET DEBUG_SYNC= 'row_merge_after_scan
 SIGNAL opened WAIT_FOR flushed';
 ALTER TABLE t1 FORCE, ADD COLUMN k4 int;
@@ -100,6 +101,7 @@ SELECT COUNT(k1),k2,k3 FROM t1 GROUP BY k2,k3;
 COUNT(k1)	k2	k3
 480	aaa	bbb
 480	aaaa	bbbb
+1	test	test
 disconnect con1;
 connection default;
 show create table t1;
@@ -109,14 +111,15 @@ t1	CREATE TABLE `t1` (
   `k2` char(200) DEFAULT NULL,
   `k3` char(200) DEFAULT NULL,
   PRIMARY KEY (`k1`)
-) ENGINE=InnoDB AUTO_INCREMENT=1023 DEFAULT CHARSET=latin1
+) ENGINE=InnoDB AUTO_INCREMENT=1024 DEFAULT CHARSET=latin1
 drop table t1;
 drop table t480;
 #
 # MDEV-12827 Assertion failure when reporting duplicate key error
 # in online table rebuild
 #
 CREATE TABLE t1 (j INT UNIQUE, i INT UNIQUE) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(2, 2);
 connect  con1,localhost,root,,test;
 SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL built WAIT_FOR log';
 ALTER TABLE t1 DROP j, FORCE;
diff --git a/mysql-test/suite/innodb/r/innodb-index-online.result b/mysql-test/suite/innodb/r/innodb-index-online.result
@@ -509,6 +509,7 @@ DROP TABLE t1;
 # MDEV-13205 assertion !dict_index_is_online_ddl(index) upon ALTER TABLE
 #
 CREATE TABLE t1 (c VARCHAR(64)) ENGINE=InnoDB;
+INSERT INTO t1 VALUES('foo');
 SET DEBUG_SYNC = 'row_log_apply_before SIGNAL t1u_created WAIT_FOR dup_done';
 ALTER TABLE t1 ADD UNIQUE(c);
 connection con1;
diff --git a/mysql-test/suite/innodb/r/instant_alter_debug.result b/mysql-test/suite/innodb/r/instant_alter_debug.result
@@ -171,6 +171,7 @@ connect stop_purge,localhost,root;
 START TRANSACTION WITH CONSISTENT SNAPSHOT;
 connect ddl,localhost,root,,test;
 DELETE FROM t1;
+INSERT INTO t1 VALUES(1, 2);
 SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL copied WAIT_FOR logged';
 ALTER TABLE t1 FORCE;
 connection default;
@@ -449,6 +450,7 @@ DROP TABLE t1;
 CREATE TABLE t1
 (a INT NOT NULL, b INT, c INT, d INT, e INT, f INT, g INT, h INT, i TEXT)
 ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1, 2, 3, 4, 5, 6, 7, 8, "test");
 ALTER TABLE t1 MODIFY a INT NULL;
 SET DEBUG_SYNC='innodb_inplace_alter_table_enter SIGNAL alter WAIT_FOR go';
 ALTER TABLE t1 ADD PRIMARY KEY (a);
@@ -462,6 +464,7 @@ connection default;
 disconnect con1;
 SELECT * FROM t1;
 a	b	c	d	e	f	g	h	i
+1	2	3	4	5	6	7	8	test
 DROP TABLE t1;
 SET DEBUG_SYNC=RESET;
 # End of 10.4 tests
diff --git a/mysql-test/suite/innodb/t/alter_candidate_key.test b/mysql-test/suite/innodb/t/alter_candidate_key.test
@@ -24,6 +24,7 @@ CREATE TABLE t1(f1 INT, f2 INT,
 		PRIMARY KEY(f1, f2),
 		UNIQUE INDEX uidx2 (f1, f2),
 		UNIQUE INDEX uidx1 (f2))ENGINE=InnoDB;
+INSERT INTO t1 VALUES(2, 2);
 ALTER TABLE t1 DROP PRIMARY KEY;
 SHOW CREATE TABLE t1;
 SET DEBUG_SYNC = 'innodb_inplace_alter_table_enter
@@ -42,6 +43,7 @@ DROP TABLE t1;
 
 SET SQL_MODE= strict_trans_tables;
 CREATE TABLE t1(a INT UNIQUE) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1);
 SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL dml WAIT_FOR dml_done';
 --send ALTER TABLE t1 MODIFY COLUMN a INT NOT NULL
 connection con1;
diff --git a/mysql-test/suite/innodb/t/alter_not_null_debug.test b/mysql-test/suite/innodb/t/alter_not_null_debug.test
@@ -75,7 +75,7 @@ SET DEBUG_SYNC='RESET';
 --echo #
 CREATE TABLE t1 (f VARCHAR(8) CHARACTER SET latin1 COLLATE latin1_swedish_ci)
 ENGINE=InnoDB;
-
+INSERT INTO t1 VALUES('ZERO');
 connection con1;
 SET DEBUG_SYNC = 'row_log_table_apply1_before SIGNAL scanned WAIT_FOR insert_done';
 send ALTER TABLE t1 MODIFY f VARCHAR(256) COLLATE latin1_german2_ci NOT NULL;
diff --git a/mysql-test/suite/innodb/t/alter_primary_key.test b/mysql-test/suite/innodb/t/alter_primary_key.test
@@ -9,6 +9,7 @@
 
 CREATE TABLE t0 (pk INT PRIMARY KEY) ENGINE=InnoDB;
 CREATE TABLE t1 (c CHAR(2) NOT NULL) ENGINE=InnoDB;
+INSERT INTO  t1 VALUES('cd');
 
 connect (con1,localhost,root,,);
 BEGIN;
diff --git a/mysql-test/suite/innodb/t/ddl_purge.test b/mysql-test/suite/innodb/t/ddl_purge.test
@@ -4,6 +4,7 @@
 
 CREATE TABLE t0 (pk INT PRIMARY KEY) ENGINE=InnoDB;
 CREATE TABLE t1 (pk INT PRIMARY KEY, b INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(100, 100);
 
 --connect (con1,localhost,root,,test)
 BEGIN;
diff --git a/mysql-test/suite/innodb/t/innodb-alter-tempfile.test b/mysql-test/suite/innodb/t/innodb-alter-tempfile.test
@@ -80,7 +80,7 @@ BEGIN;
 DELETE FROM mysql.innodb_table_stats;
 
 connect (con2,localhost,root,,);
-SET DEBUG_SYNC='inplace_after_index_build SIGNAL blocked WAIT_FOR ever';
+SET DEBUG_SYNC='innodb_inplace_alter_table_enter SIGNAL blocked WAIT_FOR ever';
 send ALTER TABLE t1 FORCE;
 
 connection default;
diff --git a/mysql-test/suite/innodb/t/innodb-index-debug.test b/mysql-test/suite/innodb/t/innodb-index-debug.test
@@ -96,6 +96,7 @@ drop table t1;
 # Log file creation failure.
 create table t1(k1 int auto_increment primary key,
 k2 char(200),k3 char(200))engine=innodb;
+INSERT INTO t1 VALUES(1, "test", "test");
 SET DEBUG_SYNC= 'row_merge_after_scan
 SIGNAL opened WAIT_FOR flushed';
 send ALTER TABLE t1 FORCE, ADD COLUMN k4 int;
@@ -122,6 +123,7 @@ drop table t480;
 --echo #
 
 CREATE TABLE t1 (j INT UNIQUE, i INT UNIQUE) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(2, 2);
 --connect (con1,localhost,root,,test)
 SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL built WAIT_FOR log';
 --send
diff --git a/mysql-test/suite/innodb/t/innodb-index-online.test b/mysql-test/suite/innodb/t/innodb-index-online.test
@@ -477,6 +477,7 @@ DROP TABLE t1;
 --echo # MDEV-13205 assertion !dict_index_is_online_ddl(index) upon ALTER TABLE
 --echo #
 CREATE TABLE t1 (c VARCHAR(64)) ENGINE=InnoDB;
+INSERT INTO t1 VALUES('foo');
 SET DEBUG_SYNC = 'row_log_apply_before SIGNAL t1u_created WAIT_FOR dup_done';
 send ALTER TABLE t1 ADD UNIQUE(c);
 
diff --git a/mysql-test/suite/innodb/t/instant_alter_debug.test b/mysql-test/suite/innodb/t/instant_alter_debug.test
@@ -186,6 +186,7 @@ connect stop_purge,localhost,root;
 START TRANSACTION WITH CONSISTENT SNAPSHOT;
 connect ddl,localhost,root,,test;
 DELETE FROM t1;
+INSERT INTO t1 VALUES(1, 2);
 SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL copied WAIT_FOR logged';
 send ALTER TABLE t1 FORCE;
 connection default;
@@ -519,7 +520,7 @@ DROP TABLE t1;
 CREATE TABLE t1
 (a INT NOT NULL, b INT, c INT, d INT, e INT, f INT, g INT, h INT, i TEXT)
 ENGINE=InnoDB;
-
+INSERT INTO t1 VALUES(1, 2, 3, 4, 5, 6, 7, 8, "test");
 ALTER TABLE t1 MODIFY a INT NULL;
 
 SET DEBUG_SYNC='innodb_inplace_alter_table_enter SIGNAL alter WAIT_FOR go';
diff --git a/mysql-test/suite/innodb_fts/r/misc_debug.result b/mysql-test/suite/innodb_fts/r/misc_debug.result
@@ -30,6 +30,7 @@ DROP TABLE t2, t1;
 # MDEV-25200 Index count mismatch due to aborted FULLTEXT INDEX
 #
 CREATE TABLE t1(a INT, b TEXT, c TEXT, FULLTEXT INDEX(b)) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1, "test", "test_1");
 connect con1,localhost,root,,test;
 SET DEBUG_DBUG="+d,innodb_OOM_inplace_alter";
 SET DEBUG_SYNC='innodb_commit_inplace_alter_table_enter SIGNAL s2 WAIT_FOR g2';
@@ -39,6 +40,7 @@ SET DEBUG_SYNC='now WAIT_FOR s2';
 START TRANSACTION;
 SELECT * FROM t1;
 a	b	c
+1	test	test_1
 SET DEBUG_SYNC='now SIGNAL g2';
 connection con1;
 ERROR HY000: Out of memory.
diff --git a/mysql-test/suite/innodb_fts/t/misc_debug.test b/mysql-test/suite/innodb_fts/t/misc_debug.test
@@ -59,6 +59,7 @@ DROP TABLE t2, t1;
 --echo # MDEV-25200 Index count mismatch due to aborted FULLTEXT INDEX
 --echo #
 CREATE TABLE t1(a INT, b TEXT, c TEXT, FULLTEXT INDEX(b)) ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1, "test", "test_1");
 connect(con1,localhost,root,,test);
 SET DEBUG_DBUG="+d,innodb_OOM_inplace_alter";
 SET DEBUG_SYNC='innodb_commit_inplace_alter_table_enter SIGNAL s2 WAIT_FOR g2';
diff --git a/sql/handler.h b/sql/handler.h
@@ -2493,6 +2493,9 @@ class Alter_inplace_info
   /** true when InnoDB should abort the alter when table is not empty */
   bool error_if_not_empty;
 
+  /** True when DDL should avoid downgrading the MDL */
+  bool mdl_exclusive_after_prepare= false;
+
   Alter_inplace_info(HA_CREATE_INFO *create_info_arg,
                      Alter_info *alter_info_arg,
                      KEY *key_info_arg, uint key_count_arg,
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
@@ -7709,15 +7709,16 @@ static bool mysql_inplace_alter_table(THD *thd,
     lock for prepare phase under LOCK TABLES in the same way as when
     exclusive lock is required for duration of the whole statement.
   */
-  if (inplace_supported == HA_ALTER_INPLACE_EXCLUSIVE_LOCK ||
-      ((inplace_supported == HA_ALTER_INPLACE_COPY_NO_LOCK ||
+  if (!ha_alter_info->mdl_exclusive_after_prepare &&
+      (inplace_supported == HA_ALTER_INPLACE_EXCLUSIVE_LOCK ||
+       ((inplace_supported == HA_ALTER_INPLACE_COPY_NO_LOCK ||
         inplace_supported == HA_ALTER_INPLACE_COPY_LOCK ||
         inplace_supported == HA_ALTER_INPLACE_NOCOPY_NO_LOCK ||
         inplace_supported == HA_ALTER_INPLACE_NOCOPY_LOCK ||
         inplace_supported == HA_ALTER_INPLACE_INSTANT) &&
        (thd->locked_tables_mode == LTM_LOCK_TABLES ||
         thd->locked_tables_mode == LTM_PRELOCKED_UNDER_LOCK_TABLES)) ||
-      alter_info->requested_lock == Alter_info::ALTER_TABLE_LOCK_EXCLUSIVE)
+      alter_info->requested_lock == Alter_info::ALTER_TABLE_LOCK_EXCLUSIVE))
   {
     if (wait_while_table_is_used(thd, table, HA_EXTRA_FORCE_REOPEN))
       goto cleanup;
diff --git a/storage/innobase/handler/handler0alter.cc b/storage/innobase/handler/handler0alter.cc
@@ -1949,10 +1949,15 @@ innobase_fts_check_doc_id_col(
 }
 
 /** Check whether the table is empty.
-@param[in]	table	table to be checked
+@param[in]	table			table to be checked
+@param[in]	ignore_delete_marked	Ignore the delete marked
+					flag record
 @return true if table is empty */
-static bool innobase_table_is_empty(const dict_table_t *table)
+static bool innobase_table_is_empty(const dict_table_t *table,
+				    bool ignore_delete_marked=true)
 {
+  if (!table->space)
+    return false;
   dict_index_t *clust_index= dict_table_get_first_index(table);
   mtr_t mtr;
   btr_pcur_t pcur;
@@ -1991,12 +1996,16 @@ static bool innobase_table_is_empty(const dict_table_t *table)
   }
 
   rec= page_cur_get_rec(cur);
-  if (rec_get_deleted_flag(rec, dict_table_is_comp(table)));
-  else if (!page_rec_is_supremum(rec))
+  if (rec_get_deleted_flag(rec, dict_table_is_comp(table)))
   {
+    if (ignore_delete_marked)
+      goto scan_leaf;
+non_empty:
     mtr.commit();
     return false;
   }
+  else if (!page_rec_is_supremum(rec))
+    goto non_empty;
   else
   {
     next_page= true;
@@ -6853,6 +6862,7 @@ prepare_inplace_alter_table_dict(
 		DBUG_ASSERT(num_fts_index <= 1);
 		DBUG_ASSERT(!ctx->online || num_fts_index == 0);
 		DBUG_ASSERT(!ctx->online
+			    || !ha_alter_info->mdl_exclusive_after_prepare
 			    || ctx->add_autoinc == ULINT_UNDEFINED);
 		DBUG_ASSERT(!ctx->online
 			    || !innobase_need_rebuild(ha_alter_info, old_table)
@@ -7666,6 +7676,20 @@ ha_innobase::prepare_inplace_alter_table(
 		DBUG_RETURN(false);
 	}
 
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+	if (table->part_info == NULL) {
+#endif
+	/* Ignore the MDL downgrade when table is empty.
+	This optimization is disabled for partition table. */
+	ha_alter_info->mdl_exclusive_after_prepare =
+		innobase_table_is_empty(m_prebuilt->table, false);
+	if (ha_alter_info->online
+	    && ha_alter_info->mdl_exclusive_after_prepare) {
+		ha_alter_info->online = false;
+	}
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+	}
+#endif
 	indexed_table = m_prebuilt->table;
 
 	/* ALTER TABLE will not implicitly move a table from a single-table
@@ -8450,7 +8474,9 @@ ha_innobase::inplace_alter_table(
 
 	DEBUG_SYNC(m_user_thd, "innodb_inplace_alter_table_enter");
 
-	if (!(ha_alter_info->handler_flags & INNOBASE_ALTER_DATA)) {
+	/* Ignore the inplace alter phase when table is empty */
+	if (!(ha_alter_info->handler_flags & INNOBASE_ALTER_DATA)
+	    || ha_alter_info->mdl_exclusive_after_prepare) {
 ok_exit:
 		DEBUG_SYNC(m_user_thd, "innodb_after_inplace_alter_table");
 		DBUG_RETURN(false);

Original file line number	Diff line number	Diff line change
`@@ -509,6 +509,7 @@ DROP TABLE t1;`
`509`	`509`	`# MDEV-13205 assertion !dict_index_is_online_ddl(index) upon ALTER TABLE`
`510`	`510`	`#`
`511`	`511`	`CREATE TABLE t1 (c VARCHAR(64)) ENGINE=InnoDB;`
	`512`	`+INSERT INTO t1 VALUES('foo');`
`512`	`513`	`SET DEBUG_SYNC = 'row_log_apply_before SIGNAL t1u_created WAIT_FOR dup_done';`
`513`	`514`	`ALTER TABLE t1 ADD UNIQUE(c);`
`514`	`515`	`connection con1;`