This is a separate issue to investigate possible performance degradation with semi-join as reported in MDEV-6239. We assume that MDEV-6239 is about partition pruning, and this bug will be about possible other issue.

Summary of data from comments and uploaded attachments for MDEV-6239:

MySQL_Myisam (reported response time: 1 sec)

• SJ-Materialization-lookup is used
• 842K rows read

Maria_Myisam_Optimizer_off (reported resp. time 1 second)

• Materialization is used.
• 842K row reads.

Maria_Myisam_Optimizer_On (reported resp. time 23 seconds)

• LooseScan is used.
• 7.5M row reads.
  (Need to retry this query with partition pruning fix. Maybe, the optimizer
  will figure that query plan with LooseScan is not optimal and pick a
  different plan)

Maria_Toku_Optimizer_Off (reported resp. time 10 sec)

• Materialization is used
• 845K reads

Maria_Toku_Optimizer_On (reported resp. time 5 sec)

• Materialization is used
• 842K reads