Nhibernate查询超时而SQL查询不

Question

I'm running this code to fetch data:

var docs = session.Query<Content>().Where(x =>  x.Attachments.Count > 0).Skip(pageNumber * Pagesize).Take(count).ToList();

It should get all documents with attachements. I added paging to boost it up, and not taking all documents at one step (there is about 10k documents matching and 600k all).

Query executed by NHibernate:

exec sp_executesql N'SELECT TOP (@p0) CastleId12_, Version12_, Abstract12_, Publishe4_12_, Title12_, Body12_, Brand12_, Source12_, SourceCo9_12_, IdInSource12_, Documen11_12_, HTML12_, Subscri13_12_, FileLoc14_12_, OtherMe15_12_, Companies12_, Keywords12_, Subscri18_12_, Author12_, Documen20_12_, SourceF21_12_, SourceB22_12_, UpdateDate12_, SourceU24_12_, Content25_12_, Interna26_12_, Workben27_12_, Checksum12_, Field29_12_ FROM (select content0_.CastleId as CastleId12_, content0_.Version as Version12_, content0_.Abstract as Abstract12_, content0_.PublishedDate as Publishe4_12_, content0_.Title as Title12_, content0_.Body as Body12_, content0_.Brand as Brand12_, content0_.Source as Source12_, content0_.SourceContentId as SourceCo9_12_, content0_.IdInSource as IdInSource12_, content0_.DocumentType as Documen11_12_, content0_.HTML as HTML12_, content0_.Subscriptions as Subscri13_12_, content0_.FileLocation as FileLoc14_12_, content0_.OtherMetadata as OtherMe15_12_, content0_.Companies as Companies12_, content0_.Keywords as Keywords12_, content0_.SubscriptionUpdateDate as Subscri18_12_, content0_.Author as Author12_, content0_.DocumentStatus as Documen20_12_, content0_.SourceFileExtension as SourceF21_12_, content0_.SourceBaseName as SourceB22_12_, content0_.UpdateDate as UpdateDate12_, content0_.SourceUpdateDate as SourceU24_12_, content0_.ContentUpdateDate as Content25_12_, content0_.InternalDocumentType as Interna26_12_, content0_.WorkbenchList as Workben27_12_, content0_.Checksum as Checksum12_, content0_.Field_id as Field29_12_, ROW_NUMBER() OVER(ORDER BY CURRENT_TIMESTAMP) as __hibernate_sort_row from [Content] content0_ where (select cast(count(*) as INT) from ContentAttachments attachment1_ where content0_.CastleId=attachment1_.DocumentId)>@p1) as query WHERE query.__hibernate_sort_row > @p2 ORDER BY query.__hibernate_sort_row',N'@p0 int,@p1 int,@p2 int',@p0=50,@p1=0,@p2=0

If I run it in that way it takes 1.5 minutes to execute in SSMS and of course it throws timeout exception in my app.

If I change it to:

SELECT TOP (50) CastleId12_, Version12_, Abstract12_, Publishe4_12_, Title12_, Body12_, Brand12_, Source12_, SourceCo9_12_, IdInSource12_, Documen11_12_, HTML12_, Subscri13_12_, FileLoc14_12_, OtherMe15_12_, Companies12_, Keywords12_, Subscri18_12_, Author12_, Documen20_12_, SourceF21_12_, SourceB22_12_, UpdateDate12_, SourceU24_12_, Content25_12_, Interna26_12_, Workben27_12_, Checksum12_, Field29_12_ FROM (select content0_.CastleId as CastleId12_, content0_.Version as Version12_, content0_.Abstract as Abstract12_, content0_.PublishedDate as Publishe4_12_, content0_.Title as Title12_, content0_.Body as Body12_, content0_.Brand as Brand12_, content0_.Source as Source12_, content0_.SourceContentId as SourceCo9_12_, content0_.IdInSource as IdInSource12_, content0_.DocumentType as Documen11_12_, content0_.HTML as HTML12_, content0_.Subscriptions as Subscri13_12_, content0_.FileLocation as FileLoc14_12_, content0_.OtherMetadata as OtherMe15_12_, content0_.Companies as Companies12_, content0_.Keywords as Keywords12_, content0_.SubscriptionUpdateDate as Subscri18_12_, content0_.Author as Author12_, content0_.DocumentStatus as Documen20_12_, content0_.SourceFileExtension as SourceF21_12_, content0_.SourceBaseName as SourceB22_12_, content0_.UpdateDate as UpdateDate12_, content0_.SourceUpdateDate as SourceU24_12_, content0_.ContentUpdateDate as Content25_12_, content0_.InternalDocumentType as Interna26_12_, content0_.WorkbenchList as Workben27_12_, content0_.Checksum as Checksum12_, content0_.Field_id as Field29_12_, ROW_NUMBER() OVER(ORDER BY CURRENT_TIMESTAMP) as __hibernate_sort_row from [Content] content0_ where (select cast(count(*) as INT) from ContentAttachments attachment1_ where content0_.CastleId=attachment1_.DocumentId)>0) as query WHERE query.__hibernate_sort_row > 0 ORDER BY query.__hibernate_sort_row 

(The only change is that I don't run it in sp_executesql and I'm inlining parameters) It takes about 2 seconds to execute.

Has anyone any idea how can I modify my Nhibernate query so it will work faster? I tried changing page size and page, but nothing changed. I read about sp_executesql but the only thing I found is about varchar arguments: https://stackoverflow.com/a/4540108/1714342

Why SSMS is executing it so slow?

Answer 1

You may try to :

• set an explicit OrderBy (say on primary key) in your NHibernate query (as I guess the default generated ORDER BY CURRENT_TIMESTAMP does not help the optimizer)

• replace

    .Where(x => x.Attachments.Count > 0) 

  with

    .Where(x => x.Attachments.Any()) 

  (I guess it would lead to a different generated SQL query)

Answer 2

It should get all documents with attachements.

I should recommend that instead of loading all documents, just load the basic information of the documents and show that to user. And when user actually asks you to display content of data, load that specific document.