[Mondrian] Queries being executed in serial in mondrian 3.4

Pedro Vale pedro.vale at webdetails.pt
Fri Jun 8 11:15:04 EDT 2012


Hi, Luc.

Here's the detail for the test case we have so far (tested against Mondrian trunk):

Open Analysis View - Create connection over steel-wheels and issue a top count query. We have a breakpoint set in RolapNativeTopCount so execution stops there.

Open another analysis View - Create connection over SampleData (another cube which should rule out cache sharing, I guess) . 
Mondrian is called to get that first screen, execution goes into RolapConnection.execute, shepherdExecution method is called but the executeInternal (line 628) is not called - only after execution is resumed on the previous breakpoint.


hmmm.... actually, let me rephrase that last sentence. Apparently, if I wait long enough (about 4 minutes), the second thread will go into executeInternal due to a new request coming in from JPivot... weird...

As Pedro said in another email, this does not happen in Mondrian 3.3.

I'll file a JIRA with this info so you guys can analyze this. Let me know if you need more info.

cheers,

Pedro Vale                             pedro.vale at webdetails.pt
WebDetails Consulting                    http://www.webdetails.pt




A 2012/06/08, às 15:13, Luc Boudreau escreveu:

> My guess is that dashboard B waits on some cells that are fetched by dashboard A before rendering. As of Mondrian 3.4, we do a more efficient cell sharing scheme; the cells are only loaded once, whereas before, two concurrent queries could end up executing the same request if both were issued before the cells were written to cache.
> 
> Luc
> 
> On Fri, Jun 8, 2012 at 9:31 AM, Pedro Alves <pmgalves at gmail.com> wrote:
> 
> I don't think that's the case (as we actually increased that number a
> lot) but no harm done trying
> 
> 
> However - We just tested adding a breakpoint to a topcount def fun,
> stopping there and then opening another analysis view - It was stuck
> there until we pressed continue !!
> 
> 
> I'll test this in 3.3.0 or whatever was on pentaho 4.0
> 
> 
> 
> -pedro
> 
> 
> 
> On 06/08/2012 02:27 PM, Brian Hagan wrote:
> > Pedro,
> >
> > It does ring a bell. See http://jira.pentaho.com/browse/MONDRIAN-1080. Maybe you can try 3.4.3.
> >
> > - Brian
> > On Jun 8, 2012, at 9:02 AM, Pedro Alves wrote:
> >
> >>
> >>
> >> Hey there.
> >>
> >>
> >> I really don't know how to ask this. I'm not even sure there's an issue,
> >> just a set of coincidences.
> >>
> >>
> >> As most of you know, we develop a lot of dashboards that rely on mdx.
> >> Lately, we've been having a few complains that the dashboards are
> >> incredibly slow.
> >>
> >>
> >> And we can't find, in the mondrian / sql logs reasons for that to be slow.
> >>
> >>
> >> Until we noticed somethng weird:
> >>
> >> 1. User A accesses a dashboard that is not on cache
> >> 2. User B accesses a dashboard that should be on cache
> >> 3. We see on the logs the queries for user A
> >> 4. User B is stuck, no activity
> >> 5. User A's queries end, dashboard rendered
> >> 6. User B's dashboard is immediately rendered
> >>
> >>
> >> I saw this the first time 2 weeks ago in a mondrian over lucid. I
> >> thought it had to do with lucid's connection polling.
> >>
> >>
> >> I saw this again *today* with mondrian with mysql.
> >>
> >>
> >> Common factor: They were both on pentaho 4.5 (with mondrian 3.4.1).
> >>
> >>
> >> Commented this with Jan Aertsen and he said "weird - someone mentioned
> >> something very similar a few days ago".
> >>
> >>
> >> I'm not saying this is a regression cause I don't know what it is. I
> >> know some work has been done on query execution. But it's definitely
> >> something that was not there before (or all our dashboards would be
> >> basically unusable).
> >>
> >>
> >> Does this ring any bells to anyone? We'll try to see if we can somehow
> >> reproduce this, but it's incredibly hard to reproduce concurrency
> >> issues.... :(
> >>
> >>
> >>
> >> -pedro
> >> _______________________________________________
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> >> Mondrian at pentaho.org
> >> http://lists.pentaho.org/mailman/listinfo/mondrian
> >
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