I just started observing this in our system as usage is slowly ramping up.
There appears to be JIRA issue #NH-3050 (
https://nhibernate.jira.com/browse/NH-3050 ) for this, but it is as of yet
unresolved.
On Monday, September 5, 2011 5:19:19 AM UTC-4, Yohei Iwano wrote:
>
> I'm sorry for my poor English. But this happens in our system too.
>
> At first, let me explain my understanding.
> When I query linq contains collection parameter like this
> from x in session.Query<SomeEntity> where
> collectionParam.Contains(x.Col1) select x
>
> It will process like this
>
> 1. Retrieve NhLinqExpression Query Plan from QueryPlanCache
> 2. Retrieve ExpandedQueryExpression Query Plan from QueryPlanCache
>
> but if the collection parameter contains only one value(like "var
> collectionParam = new int[] {100}").
> It will process like this
>
> 1. Retrieve NhLinqExpression Query Plan from QueryPlanCache
> 2. Retrieve NhLinqExpression(not ExpandedQueryExpression!) Query Plan
> from QueryPlanCache
>
> this happens because of problem in creation of "query plan cache key".
> When the collection parameter contains only one value,
> NhLinqExpression and ExpandedQueryExpression both make same query plan
> cache key.
> (see ExpressionQueryImpl.ExpandParameters method)
>
> Normally, this process works fine. But if the GC occurs between 1 and
> 2, and the NhLinqExpression objects are collected,
> ExpandedQueryExpression(which is the same query plan cache key as
> NhLinqExpression) is now going to cache.
> In this time, softReferenceCache object in the SoftLimitMRUCache is
> poisoned. And next time you try to execute linq, InvalidCastException
> occurs...
>
> I'm caching SessionFactory object in static field, and reuse it
> between all threads/requests. The pollution of QueryPlanCache is
> really serious problem...
> (Additionally, I'm using ThreadStaticSessionContext to share Session
> object between application layers. So I cannot recreate SessionFactory
> object easily...)
>
> Yohei
>
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