[Mondrian] Queries being executed in serial in mondrian 3.4

[Pedro Alves]

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