Question

What reasons would you NOT choose to enable forced parameterization over simple parameterization for ad-hoc queries in SQL Server?

Is there a performance overhead? If so would it not be offset by the (possible) gains made by re-used query plans?

Answer 1

Have you analyzed your plan cache to see if you have a high number of single-use plans?

SELECT usecounts, COUNT(*), SUM(size_in_bytes) 
  FROM sys.dm_exec_cached_plans
  GROUP BY usecounts
  ORDER BY usecounts;

Have you considered the ‘optimize for ad hoc workloads‘ setting, which at least only stores a stub for the plan until it has been used more than once? I’ve found this to be quite effective.

If you have a lot of ad hoc SQL and you are seeing plan cache bloat, it can’t hurt to try forced parameterization. But you should thoroughly test your entire workload, since there are cases where the overhead can outweigh the gains (in particular if you make heavy use of indexed views, persisted computed columns, or partitioning you may end up with worse plans). It is important to note that when you turn this setting on, it also runs a DBCC FREEPROCCACHE for you, so expect a little hiccup where all of your existing plans will need to be re-compiled the next time they are needed. (Of course this has far less noticeable impact in the case where you already have ‘optimize for ad hoc’ combined with lots of single-use plans, since you’re mostly evicting stubs that would probably get flushed before re-used anyway.)

Also note that there are many cases where this setting has no effect on individual queries (see the Books Online topic).