MDEV-20131 Assertion `!pk->has_virtual ()' failed in instant_alter_column_possiblebb-10.4-20131

Problem:- Primary key on long unique columns is not allowed but when
`CREATE TABLE t2 (a TEXT, PRIMARY KEY(a(1871))) ENGINE=InnoDB;`
is executed with innodb_page_size=8k or 4k, primary key on DB_ROW_HASH_1 column
is created. Reason of this is in mysql_prepare_create_table we check against
max_key_part_length() to see whether key_part length is more then engine supported
key_part length , and if it is true error is thrown for primary key and long
unique index is created for unique key. But in this case max_key_part_length()
returns 3072 which is more the max_key_length() , which later in code triggers
creating of long unique index.

Solution:- max_supported_key_part_length() should return according to innodb
page size.

4 files changed, 25 insertions, 9 deletions

diff --git a/mysql-test/main/long_unique_bugs.opt b/mysql-test/main/long_unique_bugs.opt
new file mode 100644
index 00000000000..058a129cdc2
--- /dev/null
+++ b/mysql-test/main/long_unique_bugs.opt
@@ -0,0 +1 @@
+--innodb-page-size=8K
diff --git a/mysql-test/main/long_unique_bugs.result b/mysql-test/main/long_unique_bugs.result
index 5d6c0562c8a..e1c5738e2aa 100644
--- a/mysql-test/main/long_unique_bugs.result
+++ b/mysql-test/main/long_unique_bugs.result
@@ -148,7 +148,7 @@ ALTER TABLE t1 DROP KEY f, ADD INDEX idx1(f), ALGORITHM=INSTANT;
 ERROR 0A000: ALGORITHM=INSTANT is not supported. Reason: ADD INDEX. Try ALGORITHM=NOCOPY
 ALTER TABLE t1 ADD KEY idx2(f);
 Warnings:
-Note	1071	Specified key was too long; max key length is 3072 bytes
+Note	1071	Specified key was too long; max key length is 1536 bytes
 DROP TABLE t1;
 CREATE TABLE t1(a blob , b blob , unique(a,b));
 alter table t1 drop column b;
@@ -288,3 +288,5 @@ Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_par
 t2	0	a	1	a	A	NULL	NULL	NULL	YES	HASH		
 t2	0	a	2	b	A	NULL	NULL	NULL	YES	HASH		
 DROP TABLE t1,t2;
+CREATE TABLE t2 (a TEXT, PRIMARY KEY(a(1871))) ENGINE=InnoDB;
+ERROR 42000: Specified key was too long; max key length is 1536 bytes
diff --git a/mysql-test/main/long_unique_bugs.test b/mysql-test/main/long_unique_bugs.test
index 34d02b1c8f4..b38ce881802 100644
--- a/mysql-test/main/long_unique_bugs.test
+++ b/mysql-test/main/long_unique_bugs.test
@@ -368,3 +368,9 @@ show index from t2;
 
 # Cleanup
 DROP TABLE t1,t2;
+
+#
+# MDEV-20131 Assertion `!pk->has_virtual ()' failed in instant_alter_column_possible
+#  (.opt file is created which will make innodb_page_size=8k)
+--error ER_TOO_LONG_KEY
+CREATE TABLE t2 (a TEXT, PRIMARY KEY(a(1871))) ENGINE=InnoDB;
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index ce2e4b6990f..e5e864bffc5 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -6537,14 +6537,21 @@ ha_innobase::clone(
 	DBUG_RETURN(new_handler);
 }
 
-
-uint
-ha_innobase::max_supported_key_part_length() const
-/*==============================================*/
-{
-	/* A table format specific index column length check will be performed
-	at ha_innobase::add_index() and row_create_index_for_mysql() */
-	return(REC_VERSION_56_MAX_INDEX_COL_LEN);
+uint ha_innobase::max_supported_key_part_length() const
+{
+  /* A table format specific index column length check will be performed
+  at ha_innobase::add_index() and row_create_index_for_mysql() */
+  /* FIXME: rewrite this as well as ha_innobase::max_supported_key_length()
+  using an API that considers the PRIMARY KEY as well as secondary index
+  metadata and the ROW_FORMAT and KEY_BLOCK_SIZE */
+  switch (srv_page_size) {
+  case 4096:
+    return 1173;
+  case 8192:
+    return 1536;
+  default:
+    return REC_VERSION_56_MAX_INDEX_COL_LEN;
+  }
 }
 
 /******************************************************************//**