MDEV-18875 Assertion `thd->transaction.stmt.ha_list == __null || trans == &thd->transaction.stmt' failed or bogus ER_DUP_ENTRY upon ALTER TABLE with versioning

Cause:
* when autocommit=0 (or transaction is issued by user),
 `ha_commit_trans` is called twice on ALTER TABLE, causing a duplicated
 insert into `transaction_registry` (ER_DUP_ENTRY).

Solution:
* ALTER TABLE makes an implicit commit by a second call. We actually
 need to make an insert only when it is a real commit. So is_real
 variable is additionally checked.

2 files changed, 28 insertions, 0 deletions

diff --git a/mysql-test/suite/versioning/r/trx_id.result b/mysql-test/suite/versioning/r/trx_id.result
index 413272f55f9..7c4a540c52a 100644
--- a/mysql-test/suite/versioning/r/trx_id.result
+++ b/mysql-test/suite/versioning/r/trx_id.result
@@ -476,3 +476,16 @@ SET @@SYSTEM_VERSIONING_ALTER_HISTORY=ERROR;
 SELECT count(*) from mysql.transaction_registry where begin_timestamp>=commit_timestamp;
 count(*)
 0
+# MDEV-18875 Assertion `thd->transaction.stmt.ha_list == __null ||
+# trans == &thd->transaction.stmt' failed or bogus ER_DUP_ENTRY upon
+# ALTER TABLE with versioning
+create or replace table t (x int) engine=innodb;
+set autocommit= 0;
+alter table t
+algorithm=copy,
+add column row_start bigint unsigned as row start,
+add column row_end bigint unsigned as row end,
+add period for system_time(row_start,row_end),
+with system versioning;
+set autocommit= 1;
+create or replace database test;
diff --git a/mysql-test/suite/versioning/t/trx_id.test b/mysql-test/suite/versioning/t/trx_id.test
index 617c46a9332..97935ffc975 100644
--- a/mysql-test/suite/versioning/t/trx_id.test
+++ b/mysql-test/suite/versioning/t/trx_id.test
@@ -498,3 +498,18 @@ DROP TABLE t;
 SET @@SYSTEM_VERSIONING_ALTER_HISTORY=ERROR;
 
 SELECT count(*) from mysql.transaction_registry where begin_timestamp>=commit_timestamp;
+
+--echo # MDEV-18875 Assertion `thd->transaction.stmt.ha_list == __null ||
+--echo # trans == &thd->transaction.stmt' failed or bogus ER_DUP_ENTRY upon
+--echo # ALTER TABLE with versioning
+create or replace table t (x int) engine=innodb;
+set autocommit= 0;
+alter table t
+  algorithm=copy,
+  add column row_start bigint unsigned as row start,
+  add column row_end bigint unsigned as row end,
+  add period for system_time(row_start,row_end),
+  with system versioning;
+set autocommit= 1;
+
+create or replace database test;