[Mondrian] Multi-threading SQL execution

michael bienstein mbienstein at yahoo.fr
Thu Feb 8 18:25:23 EST 2007

Yes, there has been thought about it.  I'm sure Julian can fill you in.  

The main issues I see are:
1) Either you let the database do the parallelism, in which case you need to issue effectively multiple GROUP BYs in one SELECT (which is possible on some databases such as ORACLE and even MySQL with its ROLLUP option) and then disentangle the results,
but this is not a standard in SQL.
2) Or you are really running two parallel queries in two separate connections (almost no JDBC driver will allow parallel queries.  The JTS/JTA maps transaction context to thread and JDBC drivers must obey this).
3) Or you have separate databases and have obviously different Connection objects open.

In the options (2) and (3) you need to revisit the way JDBC connections are handled by Mondrian.  In option (1) you need to maintain different SQL generation strategies.  All nice ideas but a lot of work.  Yes I've thought about it.  But who can do it?  Frustrating.


----- Message d'origine ----
De : Matt Campbell <mkambol at gmail.com>
À : Mondrian developer mailing list <mondrian at pentaho.org>
Envoyé le : Jeudi, 8 Février 2007, 23h12mn 38s
Objet : [Mondrian] Multi-threading SQL execution

We've been looking into ways to 
improve performance when running against large fact tables.  One 
candidate we identified was to multi-thread SQL query execution.  As things 
stand today, in Mondrian, SQL queries are executed sequentially.  This means 
that if an MDX query involves 2 fact tables, and each fact table takes 5 seconds 
to query, that it takes Mondrian at least 10 seconds to get results.  Running 
the two queries simultaneously would likely produce much better speed (of course 
dependent on the RDBMS capacity).  

Has anyone else considered 
multi-threading SQL execution? 

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