7. Lock

• Two-phase locking (2PL)
  • expanding phase (locks are acquired & no lock is released) + shrinking phase (locks are released & no lock is acquired)
  • guarantees serializability
  • See https://en.wikipedia.org/wiki/Two-phase_locking
• Dead lock
  • Two txns sharing the same resource preventing each other from accessing the resource, resulting in both ceasing to function.
  • In InnoDB, have innodb_lock_wait_timeout (by default 50s) + innodb_deadlock_detect (could be CPU intensive)