Three onther questions: Your email is not completely clear about which version of MonetDB you're using. The last sentence suggests you're using Feb2013 SP5. Is this correct? Did you install a pre-build binary installtion (if so, which), or did you build MonetDB yourself (if so, from Mercurial source or from tarball, and using which configure options)? And on what kind of platform are you running on (hardware, OS)? Thanks! Stefan ----- Original Message -----

Dear Bryan,

unless you could share your data such that we could reproduce the problem, could you please profile both queries using TRACE, stethoscope or tomograph; cf., http://www.monetdb.org/Documentation/Cookbooks/SQLrecipes/QueryTiming and share the respective output?

Then we might be able analyze what exactly causes the performance difference between both queries.

Thanks, Stefan

Bryan Senseman wrote:

...

I have created a traditional star-schema in MonetDB, using both Linux and Windows. We are using Mondrian OLAP on top so it generates the standard OLAP-y type of query using group-bys of dimensional values. What I’m finding is that doing joins in MonetDB is extremely expensive, for example:

The following query against a fact table with 261 million rows returns in 9-11seconds consistently

select date_hour_id/10000 as date_month_id, avg(seconds) from fact_utilization_hourly group by date_month_id;

returning 41 rows, the query includes a “Trick” to get to a month_year value because the time_ids are smart keys… yyyyMMddhh.

With the following query, using standard OLAP-y syntax, the query takes over 5 mins consistently.

select year_month_value, avg(seconds) from fact_utilization_hourly f join dim_date_hour d on f.date_hour_id = d.date_hour_id group by year_month_value;

returning the same 41 rows.

I’m at a loss to figure out why this join causes a 3200% percent increase in response time. And this seems to have gotten worse in SP5 from anecdotal evidence.

Bryan

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-- | Stefan.Manegold@CWI.nl | Database Architectures (DA) | | www.CWI.nl/~manegold | Science Park 123 (L321) | | +31 (0)20 592-4212 | 1098 XG Amsterdam (NL) |

-- | Stefan.Manegold@CWI.nl | DB Architectures (DA) | | www.CWI.nl/~manegold/ | Science Park 123 (L321) | | +31 (0)20 592-4212 | 1098 XG Amsterdam (NL) |