[MDEV-22794] Avoid potential rollback segment contention with increased scalability through even distribution Created: 2020-06-04  Updated: 2020-06-17  Resolved: 2020-06-17

Status: Closed
Project: MariaDB Server
Component/s: Storage Engine - InnoDB
Affects Version/s: 10.4.13, 10.5.3
Fix Version/s: 10.5.4, 10.4.14

Type: Bug Priority: Minor
Reporter: Krunal Bauskar Assignee: Marko Mäkelä
Resolution: Fixed Votes: 0
Labels: None


 Description   
  • Currently when the rollback segment is allocated to the new booting transaction next slot/rollback-segment is allocated using a static rseg_slot counter.
  • Neither is this logic mutex protected nor is the counter atomic.
  • With increase scalability, it could potentially cause the same rollback segments to get allocated to multiple transactions when as per design allocation of rollback segment should be round-robin.
  • Fix proposes to use atomic for rseg_slot.
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