For those of you who don’t know me, I was one of the program
managers for the SQL Server 2005 Service Broker. One of the harder parts of being the Service
Broker (SSB) PM was positioning it. The
first reaction I got when I did SSB talks was usually “Is this really different
than MSMQ”? To demonstrate that Service
Broker was really much more than yet another reliable messaging product, I
worked with several of our early adopters to come up with creative uses for the
reliable, transactional, asynchronous queuing aspects of SSB. I also wrote up a few uses that may not have
ever been implemented. Here are the more
significant SSB Rube Goldberg ideas:
Data Warehouse Load Balancing
The first ever SSB customer was an internal Microsoft
reporting application. They had 4 or 5
copies of a database used for doing large ad-hoc queries. When a query came in it was routed to one of
the copies for processing. The first SSB
application was the obvious one – queries came in to a front-end server and
were put on a queue on one of the query servers for processing. The query engine would receive a message
from the queue with the query, execute the query, and return the results in a
response message. This worked well and
the transactional messaging ensured that queries weren’t lost but the customer
wanted to be more intelligent about where queries should be routed. To do this we set up a dialog timer on each
of the query servers. When the timer
expired (every 10 seconds or so) an activation procedure would gather some
statistics about running queries, processor, memory, and disk usage, etc. and
send the info to the front end server.
The front end server could then use this information to decide which
server was the least loaded and route the queries accordingly.
X-ray transmission
This one started as a SOAP toolkit question. A research project at a college had a web
service that people could use to search for and download x-rays. The problem they were running into was the
x-ray files were very large and some of the SOAP clients couldn’t handle the
large messages. We wrote a service that
broke an x-ray down into a bunch of Service Broker messages that were sent to
the SOAP server. The client would
request a message at a time and assemble the x-ray. The client could request a message as many
times as necessary. SSB would send the
same message until the client acknowledged it.
This was a pretty minor change to the web service that made it usable to
significantly more clients.
Express backup
One of the biggest pieces of negative feedback we got for
SQL Express was that since it didn’t include SQL Agent there wasn’t an easy way
to set up periodic database backups. The
Service Broker dialog timer looked like a good way to do this so I came up with
a way to backup SQL Express at any chosen interval: http://blogs.msdn.com/b/rogerwolterblog/archive/2006/04/13/575974.aspx. One of the cool things about
this is that the backup routine is implemented in the database being backed up
so if you move the database to another server, backups continue to work. I like to think of this as the first step in
the contained database effort.
Task Management
It was a pretty logical step from using SSB for scheduled
database backups to using SSB for scheduling any database command. You just need an activated stored procedure
that reads SSB messages and executes them.
Service Broker is distributed so distributed tasks just work. I had a lot of interest when I published this
article but I didn’t hear any implementation stories: http://technet.microsoft.com/en-us/magazine/2005.05.servicebroker.aspx
Windows Workflow
Service Broker was designed to support reliable,
transactional, asynchronous applications.
The typical Service Broker application queues a message to request an
action and then goes away until the action is complete and a response is
received. I always thought that pattern
looked a lot like a workflow application so one day I built a Windows Workflow
framework that used Service Broker as the eventing layer. This resulted in a reliable, transactional
infrastructure for building workflow applications. This was pretty cool because as long as the
actions the workflow invoked were transactional, the workflow was totally
reliable. The workflow application could
die at any point and Service Broker would recover and pick up where it left off
as soon as the database started again. http://blogs.msdn.com/b/rogerwolterblog/archive/2007/05/21/windows-wf-on-sql-service-broker.aspx
Well, those are my Service Broker Rube Goldberg
stories. I would be very interested in
hearing about other unique SSB applications.
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