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Asked: 2026-05-29T11:30:47+00:00

I’m dealing with nHibernate performance problem during hydration of a collection. The nHibernate-generated query

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I’m dealing with nHibernate performance problem during hydration of a collection. The nHibernate-generated query finishes in 1-3 seconds, but the hydration takes another 7-9 seconds for just 50-90 objects. There are multiple layers of joined objects being hydrated from one resultset and data doesn’t overlap much to benefit from caching. Taking out nHibernate is out of the question and I’m simply figuring out how to make hydration faster.

One idea that I looking into is to split nHibernate code to use named queries and to control how objects in different layers are hydrated. I also found the use_reflection_optimizer parameter for nHibernate. While it seems great, there is barely any info on usage.

1) Is reflection optimizer enabled by default? I’m using .NET 4.0, so it seems that it should be turned on by default, but I can’t find a clear answer to this.

2) If use_reflection_optimizer is not “true” by default, then how do I enable it? It doesn’t work for me through web.config and I’m reading that it should be done through code or through section in config. Could someone provide an example?

3) Are there any other suggestions for speeding up hydration of my objects?

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  1. Editorial Team

    use_reflection_optimizer is enabled by default, and what it does is it generates a lot of runtime-needed reflection functionality at startup, instead when coming in contact with some objects for the first time. It makes startup longer, but it is better in the long run.

    I think NHibernate translates named HQL queries to SQL even without reflection-optimizer.

    Now, about the performance of that query, could you share some code? Could eager fetch / join help ?

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