[Mondrian] Queries being executed in serial in mondrian 3.4

Pedro Alves pmgalves at gmail.com
Fri Jun 8 10:57:40 EDT 2012


We just tested it - adding a breakpoint to a topcount fun and then 
trying to open a new analysis view, it just blocks the entire thing. In 
3.3.0 this didn't happen.


Whatever optimization was done, it's having the effect of queries not 
being paralelized *at all*


We'll open a bug, this is absolutely blocker for us


-pedro


On Fri 08 Jun 2012 03:13:24 PM WEST, Luc Boudreau wrote:
> 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
> <mailto: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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