So I've been at TechEd this week working as a Technical Learning Guide (helping out in the Hands-On Labs area). While there are good opportunities at times to share what I know (and l learn what I don't know), there's been a fair amount of time answering more basic questions than I'd like (such as "Where can I sit"). Don't get me wrong, I love doing this stuff, but I'm jealous of Kalen and Kevin as such :)
Speaking of Kalen, I attended her "birds-of-a-feather" discussion on concurrency. Very interested, especially when the discussion touched snapshot isolation. As Kalen will probably point out in detail, one of the items that many people seemed to be keen on was using the NO LOCK hint within queries. It turns out that isn't the best thing for the Lock Manger (and performance in general).
I usually describe the Lock Manager as a sort of Hindu diety, with multiple arms juggling a number of factors to try to maintain the highest level of concurrency and consistency it can. NO LOCK essentially tells the Lock Manager to go take a break - which means the Lock Manager can't factor NO LOCK queries into the entire locking equation (Hindu diety with a pair or two of handcuffs on them).
To make things worse, using Snapshot Isolation and NO LOCK hints is basically a waste of resources - NO LOCK bypasses even Snapshot Isolation (as Kalen put it - "All bets are off" when using NO LOCK). (NOTE: Kalen, please feel free to beat me with a stick if I've misworded).
The bottom line I try to impress on my clients and students is to fully understand locking, concurrency and consistency as they pertain to SQL Server. Other DB platforms use different locking models - that doesn't necessarily mean they're better, just different. Be sure to understand the locking technique you are working with before writing even a single SELECT statement.
All in all TechEd has been fun, met lots of people I haven't seen in ages, hear stories I'd rather forget (like falling down a flight of stairs in Denmark), and hearing questions and situations that I've not yet considered. If you haven't been to a TechEd, I highly recommend it. It can be both an edifying experience as well as a humbling one.
More on Snapshot Isolation, lock hints and other items to follow soon!