Before I go on about how adding an index can fix your blocking and deadlocking problems, let me warn you about how indexes can cause you problems.
Without fail, whenever I suggest adding indexes to clients, someone gets real worried about write speeds.
Like, the server can be burning down, spurting blood everywhere, and cursing our mothers in ancient Aramaic, but no, let’s stop and worry about write speeds going up by a few milliseconds.
Fully agreed: the marginal cost of an index is rarely noticeable and the marginal benefit of a well-designed index serving an existing customer base is significantly higher than its marginal cost. However, when I click that plus sign next to the Indexes folder and SSMS starts spinning because it needs to enumerate the dozens and dozens of indexes on that table, it’s a bad sign. Especially when 90% of them have “_dta_” in the name.
Click through for more thoughts on indexing, scans, and transactions.