[nhibernate-issues] [JIRA] Commented: (NH-859) Improve SubselectFetch performance

[NHibernate J. <mik...@us...>]

     [ http://jira.nhibernate.org/browse/NH-859?page=comments#action_15200 ]
     
Ken Tong commented on NH-859:
-----------------------------

>From Almas' example, only 1 call to Loader.CreateSubselects(). But it ends up creating 1000 SubselectFetch instances. Digging deeper to the source code find out the 1000 instances are identical.

In fact, there is only 1 sub-select in the generated SQL SELECT.

Would we create only 1 SubselectFetch?

How about replace

///////////////////////////////////////////////////
foreach (EntityKey[] rowKeys in keys)
{
    for (int i = 0; i < rowKeys.Length; i++)
    {
        if (rowKeys[i] != null && loadables[i].HasSubselectLoadableCollections)
        {
            SubselectFetch subselectFetch = new SubselectFetch(
                //getSQLString(), 
                aliases[i],
                loadables[i],
                queryParameters,
                keySets[i],
                namedParameterLocMap
                );

            session.BatchFetchQueue.AddSubselect(rowKeys[i], subselectFetch);
        }
    }
}
///////////////////////////////////////////////////

with

///////////////////////////////////////////////////
SubselectFetch[] subselectFetchCache = new SubselectFetch[loadables.Length];

foreach (EntityKey[] rowKeys in keys)
{
    for (int i = 0; i < rowKeys.Length; i++)
    {
        if (rowKeys[i] != null && loadables[i].HasSubselectLoadableCollections)
        {
            SubselectFetch subselectFetch = subselectFetchCache[i];

            if (subselectFetch == null)
            {
                subselectFetch = new SubselectFetch(
                    //getSQLString(), 
                    aliases[i],
                    loadables[i],
                    queryParameters,
                    keySets[i],
                    namedParameterLocMap
                    );
                subselectFetchCache[i] = subselectFetch;
            }

            session.BatchFetchQueue.AddSubselect(rowKeys[i], subselectFetch);
        }
    }
}
///////////////////////////////////////////////////


It's only an idea. I tried the current unit tests and they don't smell bad.

> Improve SubselectFetch performance
> ----------------------------------
>
>          Key: NH-859
>          URL: http://jira.nhibernate.org/browse/NH-859
>      Project: NHibernate
>         Type: Patch
>   Components: Core
>     Versions: 1.2.0.Beta3
>     Reporter: Sergey Koshcheyev
>     Priority: Trivial
>      Fix For: 1.2.0.CR1
>  Attachments: NH-859 CompareInfo.diff, NH-859.diff
>
> http://forum.hibernate.org/viewtopic.php?p=2336860#2336860
> SubselectFetch constructor takes a relatively long time to execute.

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