1. Lock, Block, and Two Smoking CPUs
Implementing Application Locking with sp_getapplock
I was thinking of using a few other titles, “There and Lock again, A DBA’s holiday”

2. Daniel R. Maenle Junior Database Administrator at ScriptPro
Pharmacy for 8+ years
OptumRX and ScriptPro
Pharmacy IT 6+ years
Junior DBA 2 years in January
2 | Introduction

3. Agenda Intro to our workflow (Quick Overview) Table Locking
Why application locks are needed?
Table Locking
Switching to sp_getapplock
Using sp_getapplock
Demos
What’s next?
Q/A
3 | Agenda

4. Pharmacy Workflow Involved: Script Drug Insurance POS
Jenny brings in prescription RX#

5. Our Original Method ScriptPro functionality
Using an “Application_lock” table
Handled table name, row_id and other lock information (application, timestamp)
Insert when using / Delete when done.
Queries written to poll this table
Debugging from this table
5 | Table Locking

6. Benefits of Using Table Locking
Central point of locking
Easy to view locks
Simplified debugging
What is locked?
SELECT * FROM Application_lock
Transaction logging
6 | Table Locking

7. Downsides of Table Locking
Single table contention
Insert/Update/Delete schema locks
Waiting on other queries before next insert/delete
Isn’t really a lock!
Concurrency
Non-requester can delete the lock!
What happened to what I was working on?
7 | Table Locking

8. The Project “Make our locking mechanism better”
What caused this request?
Blocking
Duration to insert and delete was long
Wait stats were showing bad indicators of table/schema contention (LCK_M_IX)
8 | Switching to sp_getapplock

9. The Project (2) “Make our locking mechanism better” (2) Sp_getapplock
Keep current functionality
No single point of contention
Don’t break anything!
Sp_getapplock
Very promising!
9 | Switching to sp_getapplock

10. What is sp_getapplock? Built into SQL Server
No single point of contention
Not a table!
Held in memory
Session/Transaction
MSSQLSERVER likes this
10 | Using sp_getapplock

11. More on sp_getapplock Why do we need locking? No timestamp or duration
Concurrency
Immediate resolution
Timeout available
No timestamp or duration
Requires application development to use
ACID test needs locking
Shared, Update, IntentShared, IntentExclusive, or Exclusive.
Value Result
0The lock was successfully granted synchronously.
1The lock was granted successfully after waiting for other incompatible locks to be released.
-1The lock request timed out.
-2The lock request was canceled.
-3The lock request was chosen as a deadlock victim.
-999Indicates a parameter validation or other call error.
11 | Using sp_getapplock

12. Demo of Performance Old Application_lock New style sp_getapplock
Stats/duration
What locks are being used?
New style sp_getapplock
Some oddities discovered
12 | Demo’s

13. DEMOS

14. What’s Next? To maintain a VIEW instead of a table
Old procedures
Query performance
Lost timestamp
Old habits/Troubleshooting
Session mode was default
Transaction mode difficulties
14 | What’s next?

15. Future Additions Switching to transactional locking
Better management
Using tempdb for less TLOG as well
Code changes to use APPLOCK_MODE
DELETE VIEW
Continued performance tweaks
15 | What’s next?

16. Summary Application locking can be tricky
No one best way
Pro/Con Table
Sp_getapplock has its uses
LOCKING
Able to be integrated into current code
Without much pain
Albatross to carry
16 | Summary

17. Questions? Microsoft Connect: http://bit.ly/2dpGFri
Glenn Berry wait stats –
Remus Rusanu -
Paul Randal -
MSSQL Server 2014 Unleashed -
Tech NET -
Microsoft Connect:
17 | Q/A