Deadlocks - locking and waiting for the same index?

I recommend you post the actual deadlock XML. The graphical representation is not always accurate, see The puzzle of U locks in deadlock graph s. Deadlocks can happen even on deceptively simple statements on well tuned queries, due to order of applying the updates, see Read/Write deadlock And deadocks can happen even on systems that apparently are 100% safe, like the one you originally described in the post (one row update in a clustered index w/o secondary index updates, on different keys) due to hash collisions, see %%lockres%% collision probability magic marker: 16,777,215.

I recommend you post the actual deadlock XML. The graphical representation is not always accurate, see The puzzle of U locks in deadlock graphs. Deadlocks can happen even on deceptively simple statements on well tuned queries, due to order of applying the updates, see Read/Write deadlock.

And deadocks can happen even on systems that apparently are 100% safe, like the one you originally described in the post (one row update in a clustered index w/o secondary index updates, on different keys) due to hash collisions, see %%lockres%% collision probability magic marker: 16,777,215. Now I don't expect your case to be an esoteric one, in your situation what it appears to be is simply lack of information about what actually happens. Please post the exact schema definition of your data (all tables, all indexes), the exact operations that occur in each transaction involved, and the actual deadlock XML, not the graphical rendering.

I'm unable to post the full DB schema I'm afraid, although I agree, I think there is something going on that I don't think is going on (if you see what I mean). Your Read/Write deadlock link looks interesting. I wonder if I might be able to unearth something using that information.

I did try pasting in the XML but the website didn't like the formatting. – Will Calderwood Aug 23 at 16:24 some users post attachements to SO trough services like pastebin. Com or similar – Remus Rusanu Aug 23 at 16:40.

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