What Problems Does an Eager Spool Indicate

I am attempting to increase performance of an UPDATE statement. I notice an Eager Spool operation in the showplan popping up.

Eager Spools may be added for a variety of reasons, including for Halloween Protection, or to optimize I/O when maintaining nonclustered indexes.

Without seeing (even a picture of) the execution plan, it is hard to be certain which of these scenarios might apply in your particular case. If data sensitivity is a concern, consider uploading an anonymized version of the plan for analysis using SentryOne Plan Explorer.

It may well be that the Eager Spool is not the thing you should be concentrating on anyway; many factors influence the actual performance of queries that change data. If you're basing your tuning efforts on the estimated percentage cost shown for the Eager Spool operator, please consider that those estimates are generated using a model that is not intended to match the capabilities of your particular hardware configuration.

Sometimes the eager spool can be avoided when other blocking operators are in place - sorts for example. So it is a good idea to ensure that the data is already sorted by the time it reaches that stage. (missing indexes perhaps?)

If it is there for Halloween protection then as the other guys have said there is little you can do.