Service Dispatcher: The MySpace
Implementation of Service Broker
Speaker: Christa Stelzmuller
MySpace Chief Data Architect
San Francisco SQL Server User Group
September 14, 2009
Mark Ginnebaugh, User Group Leader
www.bayareasql.org

Christa Stelzmuller
Chief Data Architect at MySpace since Oct 2006
Formerly at Yahoo!
Engineering Manager
Data Architect for the Yahoo! Music Team
Specializes in very large databases with high volumes
of transactions
Tonight’s Topic: Service Dispatcher: The MySpace
Implementation of Service Broker

What is Service Broker?
Message Queue
Asynchronous
Unicast
Intra- and Inter-database, instance, and server
Integrated into the database engine
Instance level
DML extensions

Why Service Broker?
Flexible
Atomic transactions can be split across synchronous and
asynchronous work items
Work items can occur in parallel
Predictable
Asynchronous work items are processed at a constant rate
leveling peaks and valleys
Transactional
In-Database
Common administration

Challenges with Service Broker
Unicast
Communication is from a single sender to a single target
Excessive message transmission
Routing
Requires a physical route between each service
Unmanageable number of routes
Non-Intuitive
Four object types must be implemented for each service,
and up to seven understood
High learning curve for average database developer

Introducing Service Dispatcher

Core Features
Simulated Multicast
Communication is from a single sender to a specified set of
targets
Wildcard targets support simulated broadcast
Route Management
Routes to all dispatcher client enabled databases are
managed centrally
Abstraction
API for “SEND”
Friendly database names are used instead of service
broker instances

Advanced Features
Dialog Management
Technique of dialog reuse abstracted
Pooling based on spid, service, and group
Route Receipts
Used in simulated broadcast scenarios to return information
on all servers from which acknowledgement should be
expected
Extensible
Publish/Subscribe (target agnostic messages)
Notifications

Major Use Cases
Broker Gateway
Asynchronous message
delivery APIs
Load balanced farm
Abstracted data destination
Example Usage
Activities Stream

Major Use Cases
Backend Initiated
Processing
Foreign keys and
relationships spread across
many databases
Coordinated messaging
Example Usage
Profile management
Content take-downs

Major Use Cases
List Broadcast
Local data used to broadcast
updates to lists
Two views of the relationship
represented
Example Usage
Photo Tags
Friend Categories

Developer Highlights
Message Types
No need for explicit service broker message types
If needed, application message types are supported as
part of the message body
Standard set of message types, system and dispatcher
Contracts
No need for explicit service broker contracts
Each application service must contain a reference to at
least one dispatcher contract

Developer Highlights
Conversation Group Locking
Alternative to GET CONVERSATION GROUP
Dialog consolidation for performance
Requires explicit conversation group lock release
Conversation Ending
Dispatcher specific state tables
Error handling

Administrator Highlights
Build
Central catalog
Common client code deployed
Automated services
Dispatcher route creation
Client route creation
Database Configuration
GET CONVERSATION GROUP
Maximum valid groups
Dialog pool size
Dialog timeout settings

Administrator Highlights
Health & Monitoring
Reports
Scheduled
Ad-Hoc
Notifications
Automated queue reactivation
Quarantine
Ping

Unsupported Broker Features
Message Ordering
Farm of servers, random access
Dialog death & resend
Abstracted conversation management
Fire & Forget
Conversation management is tightly controlled by
dispatcher, and logic to properly handle conversation ends
and errors is built in.
Begin/End Conversation
Applications cannot control dialog state, this is entirely
managed by dispatcher

Upcoming Features
Dialog Emulation
Introducing the concept of circuits
Message sequence number
Message ordering becomes possible
Applications can control circuit state
Abstracted activation logic
RECEIVE logic abstracted
Internal broker message type handling

Service Broker Stats
Average Average Peak Max Peak Farm Total
MySpace DB Sends/Sec/Server Sends/Sec/Server Sends/Sec/Server Sends/Sec
Dispatcher 45 229 816 9,164
Profile 90 258 925 130,290
Mail 40 2,397 8,546 1,210,485
Shared 264 540 - -
Features 21 36 37 720
Average Average Peak Max Peak Farm Total
MySpace DB Rcvs/Sec/Server Rcvs/Sec/Server Rcvs/Sec/Server Receives/Sec
Dispatcher 10 33 48 1,328
Profile 60 303 432 153,015
Mail 38 3,186 4,980 1,608,930
Shared 218 351 - -
Features 18 92 119 1,840

When not to use Dispatcher
Local asynchronous messages
One-to-one messaging
When an unsupported feature is required

Alternatives to Dispatcher
Abstracted SEND logic (same as dispatcher without the
router component)
Dynamic route management (Microsoft’s solution

More Information
Case Study
http://www.microsoft.com/casestudies/Case_Study_Detail.
aspx?CaseStudyID=4000004532
Codeplex
Soon to come!

Credits
Creator & Original Concept, Mikhail Berlyant
Principal Dispatcher Architect, Mark Lovretovich
Contributors, Kevin Stephenson & Justin Engelman

To learn more or inquire about speaking opportunities, please
contact:
Mark Ginnebaugh, User Group Leader mark@designmind.com