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9. Queued Transaction
Pro cessing
545 Tran saction Pro ce ssing
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Outline
1. Introduction
2. Transactional Sem antics
3. Q ueue Manager
A ppendices
A. Marsha ling
B. Multi-tran saction R equests (workflow )
C. (A ppendix) Microsoft M essag e Queue
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9.1 Introduction
•Direct TP -a clien t sends a request to a server, waits
(synchronou sly) for the server to run the transaction
and possibly return a reply (e.g., RPC)
•Problem s with Direct TP
–Server or client-serve r com m unications is dow n
when the client wants to sen d the req u e st
–Client or client-serv er com m unications is dow n
when the serv er wants to send the rep ly
–If the serv er fa ils, how does the client find out what
happened to its outstanding requests?
– Load balancing across many serv ers
–Priority-based scheduling of busy serv ers 2/22/05 4
Persisten t Queuing
• Q ueuing -controlling work requests by moving
them through persistent transactional queues
• B enefits of queuing
–clien t can send a re q u es t to an unavailable serv er
–server can send a rep ly to an unavailable client
–since the queue is persistent, a client can (in principle)
find out the state of a requ est
– can dequeue req u e sts based on priority
– can have many se rvers feed off a single queue
Client Server
Enqueue Dequeue
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Other Benefits
• Q ueue manager as a protocol gatew ay
– need to support multiple protocols in just one system
env iro n m e n t
– can be a trusted client of other system s to bridge secu rity
barriers
• Explicit traffic control, without message loss
•Safe place to do m essa g e translation betw een
application formats
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9.2 Transaction Sem antics Server View
•The queue is a transactional resou rce manager
•Server dequeues request within a tran saction
•If the transaction abo rts, the dequeue is undone,
so the request is returned to the queue
Start
Dequeue(Req, Q1)
process request Req
Enqueue(Reply, Q2)
Commit
Client
Enqueue
Dequeue
Server’s request queue
Client’s
reply queue
Server Program
Q1
Q2
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