MDEV-7888, MDEV-7929: Parallel replication hangs sometimes on ANALYZE TABLE or DDL

The hangs occur when the group_commit_orderer object is freed before the last
mark_start_commit() call on it - this loses the wakeup to other waiting worker
threads, causing them to hang until killed manually.

The object was freed because wakeup_subsequent_commits() was called two early
in two places. For MDEV-7888, during ANALYZE TABLE, and for MDEV-7929 during
record_gtid() after processing a DDL event. The group_commit_orderer object
can be freed when its last transaction has called wait_for_prior_commit().

Fix by implementing a suspend/resume mechanism for wakeup_subsequent_commits()
that can be used in places where a transaction is committed without this being
the commit of the actual replication event group.

Also add a protection mechanism (that asserts in debug builds) which can
prevent the too-early free and hang if other similar bugs should remain in
other parts of the code.

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index 5d64837a2c1..e47d335d926 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -3682,6 +3682,15 @@ public:
     if (wait_for_commit_ptr)
       wait_for_commit_ptr->wakeup_subsequent_commits(wakeup_error);
   }
+  wait_for_commit *suspend_subsequent_commits() {
+    wait_for_commit *suspended= wait_for_commit_ptr;
+    wait_for_commit_ptr= NULL;
+    return suspended;
+  }
+  void resume_subsequent_commits(wait_for_commit *suspended) {
+    DBUG_ASSERT(!wait_for_commit_ptr);
+    wait_for_commit_ptr= suspended;
+  }
 
 private: