Marko Mäkelä added a comment - 2017-01-23 08:25 In MG-GUI-SSD2.err, I see several purge error messages before the assertion failure: 2017-01-10 9:11:11 3972 [ERROR] InnoDB: tried to purge non-delete-marked record in index `NCI_MsgID2Message_Message` of table `zissystem`.`msgid2message` … 2017-01-10 09:11:44 0x2ce4 InnoDB: Assertion failure in thread 11492 in file row0ins.cc line 277 InnoDB: Failing assertion: !cursor->index->is_committed() The data set is corrupted, and it would be interesting to know where the corruption was introduced in the first place. MySQL 5.5 already? There might have been some bug fixes in this area over the past few years, but I believe that the problem is not fully fixed. Because the problem is so hard to repeat, I think that the InnoDB delete buffering that I implemented in MySQL 5.5 could be to blame. Both the error messages and the assertion failure occur for a secondary index. See my comments in MySQL Bug #61104 . The InnoDB process of purge removes old undo log records and delete-marked index records that are no longer needed for MVCC. All purgeable records should be delete-marked in the index. The error here is that we find a record that is not delete-marked, even though it should be. Probably because purge refused to remove these records, INSERT would crash when it finds that the key already exists and is not delete-marked. I would say that this bug is a duplicate of MDEV-9663 . I had replaced the assertion failure expression with a logically equivalent one in MySQL 5.7, which was merged to MariaDB 10.2.