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SOA - Availability vs. consistency

Hello,

I had an architectural question: Could someone please explain the tradeoff between Availability and consistency in SOA?

Thanks

Houman

[455 byte] By [Houmanb] at [2007-12-25]
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# 1
Can you provide more details about what you're asking?
erikj at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 2

Well I was listening to Vogels (CTO of amazon) as he was describing amazon's internal architecture as purely service oriented. Then he went on to say that they have to consider trade offs such as availability vs consistency for each service.

I think what he was saying is that they don't run 2 phase commit trx across all thier services. Rather they have to decide which services needed 2 phase commit and sacrifice availability to achieve it. Again, this is just my guess.

So I'm not sure about any of this, and was hoping that someone who has worked on large scale soa would jump in and describe the various tradeoffs an architect needs to consider when architecting a soa system.

Thanks

Houman

Houmanb at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 3

Houman,

with respect of trade-offs and considerations, I'd suggest you the following resources

Also, check the MSDN Architecture Center at http://msdn.microsoft.com/architecture

DiegoDagum at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 4

Thanks for sharing this! I'm going to go through all of these.

Regards,

Houman

Houmanb at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 5
I've seen several Amazon architecture presentations. They never use 2 phase commit because it would jeopardize availability if one of the databases goes down in the middle of a transaction. They keep multiple copies of their critical data and these copies are updated asynchronously. This means that failures might result in some temporary data inconsistency because a all the copies aren't the same but the multiple copies ensure that no data is ever lost. The chances of failures are low enough that the risk of temporary inconsistency that may be caused by a failure is not big enough to make risk of unavailable data caused by using 2 phase commit to guarantee consistency not worthwhile.
Roger_Wolter_MS at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 6

That's great info. Do you know where I could get to see some of thier arch. presentations? Or for that matter, any large scale soa system.

Thanks

Houman

Houmanb at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 7

No, the presentations were at conferences so I'm not aware of any publically available ones. Here's what I found on MSDN searching for SOA Case Study. I'm sure there are more around but this is a start.

http://msdn2.microsoft.com/en-us/library/ms954622.aspx

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/sessfin00.asp

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/aspnetscal.asp

Roger_Wolter_MS at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
# 8
That's great. Thanks!
Houmanb at 2007-9-3 > top of Msdn Tech,Architecture,Architecture General...
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