Tracing ORM performance

Question

This isn't a question of "which is the fastest ORM", nor is it a question on "how to write good code with ORMs". This is the other side: the code's been written, it's gone live, several thousand users are hitting the application, but there's a perceived overall performance problem. A SQL Profiler trace can only be ran for a short amount of time: 5 mins gives several hundred thousand results.

The question is simply this: having used SQL Profiler to narrow down a number of slow queries (duration greater than a given amount of time), what techniques and solutions exist for tracing these SQL queries back into the problematic component? A releated question is that if a specific area is slow, how can we identify the SQL that this area is executing so it can be suitably filtered in SQL Profiler?

The background to this is that we have a rather large application with a fairly complex table structure, and is currently based around data-access via stored procedures. If a SQL performance problem arises, it's usually case of pulling out SQL profiler, find out if there's anything slow (filter by duration) or if a the area being complained about is slow (filter by stored procedure), and tune the stored procedures (or the schema - through indexing).

Now there's a push to move our code over from a mostly-sproc solution to a mostly-ORM solution, however the big push against the move is how performance problems, if they arise, can be traced back to problematic code. I've read around and it seems that more often than not, it may involve third-party tools (ORM tracing utilities like NHProf or .NET tracing utils like dottrace) that we'd need to install on the server. Now whether additional tools can be installed on a live environment is another question, so if things like this can be performed without additional tools, then that may be a bonus.

I'm mostly interested in solutions with SQL Server 2008, but it's probably generic enough for any RDBMS. As far as the ORM tech, on this I have no specific focus as nothing's currently in use, so be interested to hear how techniques differ (or are common) twixt nHibernate, fluent-nhibernate and Entity Framework. Other ORMs are welcome though if they offer something else :-)

I've read through How to find and fix performance problems (...), and I think the issue is simply the section on there that says "isolate". A problem that is easily reproducible only on a live system is going to be difficult to isolate. The figures I quoted in para 2 are figures the types of volumes that we can get from a profile as well...

If you have real-world experience of ORM tracing on live, so much the better :-)

Update, 2016-10-21: Just for completeness, we eventually solved this for NHibernate by writing code, and overriding NHibernate methods. Full details in this other SO question I asked: NHibernate and Interceptors - measuring SQL round trip times. I expect this will be a similar approach for many different ORMs.

Answer 1

There exists profilers for ORM tools, like UberProf. It finds out which SQL statements that are generated by the ORM can be problematic.

Like the select n+1 problem, for instance. These kind of tools might give you an indication of which ORM query statements result in poor SQL code, and perhaps even how you could improve them.