PS - AA : Adaptive Locking, Adaptive Callback

• Locking and Caching is adaptive.
• Can de-escalate and re-escalate.

Clients record reads and writes locally at page and object level (local locks) Server tracks cached copies at the page granularity.


Protocol for Client Read

• If object is in cache and not marked unavailable, read locally.
• Otherwise, request to server for object. 3 cases can arise.
  • No Conflict : If no other client has a write-lock on the page/object, then return page with write-locked objects marked unavailable.
  • Object Level Conflict : If some client has a W-Lock on the object then wait for release.
  • Page Level Conflict : If some client has a W-locked page, then the page lock is de-escalated by the client.
    • Gets object level W-locks at the server for updated objects.
    • Releases the page lock.
  • Proceed as one of the previous case.