Recompile And Nested Procedures

Rock Sale


While I was answering a question, I had to revisit what happens when using different flavors of recompile hints with stored procedure when they call inner stored procedures. I like when this happens, because there are so many little details I forget.

Anyway, the TL;DR is that if you have nested stored procedures, recompiling only recompiles the outer one. The inner procs — really, I should say modules, because it includes other objects that compile query plans — but hey. Now you know what I should have said.

If you want to play around with the tests, you’ll need to grab sp_BlitzCache. I’m too lazy to write plan cache queries from scratch.

Testament


The procs:

CREATE OR ALTER PROCEDURE dbo.inner_sp
AS
BEGIN

    SELECT
        COUNT_BIG(*) AS records
    FROM sys.master_files AS mf;
END;
GO 

CREATE OR ALTER PROCEDURE dbo.outer_sp
--WITH RECOMPILE /*toggle this to see different behavior*/
AS
BEGIN

    SELECT 
        COUNT_BIG(*) AS records
    FROM sys.databases AS d;
    
    EXEC dbo.inner_sp;

END;
GO

The tests:

--It's helpful to run this before each test to clear out clutter
DBCC FREEPROCCACHE;

--Look at this with and without 
--WITH RECOMPILE in the proc definition
EXEC dbo.outer_sp;

--Take out the proc-level recompile and run this
EXEC dbo.outer_sp WITH RECOMPILE;

--Take out the proc-level recompile and run this
EXEC sp_recompile 'dbo.outer_sp';
EXEC dbo.outer_sp;

--You should run these between each test to verify behavior
--If you just run them here at the end, you'll be disappointed
EXEC sp_BlitzCache 
    @DatabaseName = 'Crap', 
    @QueryFilter = 'procedure', 
    @SkipAnalysis = 1, 
    @HideSummary = 1;

EXEC sp_BlitzCache 
    @DatabaseName = 'Crap', 
    @QueryFilter = 'statement', 
    @SkipAnalysis = 1, 
    @HideSummary = 1;

Whatchalookinat?


After each of these where a recompile is applied, you should see the inner proc/statement in the BlitzCache results, but not the outer proc.

It’s important to understand behavior like this, because recompile hints are most often used to help investigate parameter sniffing issues. If it’s taking place in nested stored procedure calls, you may find yourself with a bunch of extra work to do or needing to re-focus your use of recompile hints.

Of course, this is why I much prefer option recompile hints on problem statements. You get much more reliable behavior.

And, as Paul writes:

For instances running at least SQL Server 2008 build 2746 (Service Pack 1 with Cumulative Update 5), using OPTION (RECOMPILE) has another significant advantage over WITH RECOMPILE: Only OPTION (RECOMPILE) enables the Parameter Embedding Optimization.

Thanks for reading!



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