DX Lock in index

I have just encountered a situation where we get blocking locks on indexes where the locktype is DX. I didn't think blocking occured on index for regular SQL. Does anyone recognize this or know of a document that goes into detail on DX locks. I'm not finding much detail on this locktype.

I don't have a current lock situation to pull data from, but last time the locked object seemed to map to an index. Isn't DX supposed to be a transaction lock controlling the undo and other things required for a remote incomming transaction? That is, should I expect it to block data and/or index? I'm mostly looking for verification that the current conclusion that this was in an index is unlikely and we need to track the lock next time to try to find a target more natural for DX.

Mathias

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