Join us to learn several strategies for dealing with concurrency errors like the UNABLE_TO_LOCK_ROW error in Apex . We'll also review design patterns that can fail gracefully, and even recover silently when these errors occur ? all without compromising your data integrity.

1. High reliability DML and concurrency
design patterns for Apex
Dan Appleman, Full Circle CRM, CTO
Author: Advanced Apex Programming for Salesforce.com and Force.com
@danappleman

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3. Have you ever seen…
EXCEPTION_THROWN [32]|System.QueryException: Record Currently
Unavailable: The record you are attempting to edit, or one of its related
records, is currently being modified by another user. Please try again.
Or
FATAL_ERROR System.DmlException: Update failed. First exception on
row 0 with id ……………; first error: UNABLE_TO_LOCK_ROW, unable
to obtain exclusive access to this record: []

4. Concurrency Problems
The most dangerous kind of bug in all of computer science.
Why? Because concurrency problems and bugs can be:
▪Virtually impossible to detect
▪Virtually impossible to reproduce

5. Most of us learn about concurrency errors as
children…
Dad, can we go to
the party?
Let me think: NO!

6. Most of us learn about concurrency errors as
children…
Dad, can we go to
the party?
Let me think: NO!
15 seconds later
Mom can we go to
the party?
Sure, why not?

7. … or as parents
Dad, can we go to
the party?
Let me check with
your mom
Pessimistic locking
Mom can we go to
the party?
What did your dad say?
Optimistic locking

8. …or in Salesforce
Two Salespeople receive simultaneous instructions from two
different contacts on an opportunity…
This would be very bad

9. …or in Salesforce
Two Salespeople receive simultaneous instructions from two
different contacts on an opportunity…
Salesforce detects the
other users’ modification
Optimistic locking (so to speak)
APEX DOES NOT DO THIS!

10. …or in Salesforce
Two Salespeople receive simultaneous instructions from two
different contacts on an opportunity…
SOQL “For Update” Query
Pessimistic locking
Block another thread > 10 seconds =
UNABLE_TO_LOCK_ROW error

11. Common Lock Conditions
▪ Data skew
▪ Insert or owner change can lock a parent during sharing calculations
▪ After a record update
▪ Records have to be locked to allow rollback in case of an exception
▪ “For Update” query
▪ Explicit lock

12. Common Lock Solutions
▪ Data skew
▪ Reassign record ownership
▪ After a record update
▪ Defer record updates to the end of the execution context
▪ “For Update” query
▪ Avoid or delay where possible
▪ You cannot absolutely prevent these errors
▪ More common on high traffic systems with lots of code

13. Reproducing Lock Errors
▪ Use future calls and anonymous Apex
▪ You can simulate them in unit tests

14. Handling Lock Errors
▪ In triggers and VisualForce
▪ Let the user deal with them
▪ In asynchronous code
▪ Logging
▪ Recovery

15. For More Information
Advanced Apex Programming for Salesforce.com and Force.com –
Second Edition
•
•
•
•
•
Incorporates changes through Winter 14
Designing for CPU Time limits
Extended chapter on triggers
Extended chapter on asynchronous patterns
New chapter on concurrency patterns

16. All About Full Circle CRM
Full Circle CRM develops native Salesforce.com applications
that enable marketers to accurately track and measure
marketing campaign performance directly in Salesforce
▪ Bridge the information gap between leads and contacts
▪ Obtain complete and detailed campaign performance metrics
▪ Develop advanced campaign attribution and influence analytics
Booth 1324 Moscone North

17. Download sample code for this session at
www.AdvancedApex.com/Dreamforce13

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