Re: User Defined Aggregations in MonetDB?

Actually, there is no typo there. You have to check out gdk.h which is one of the first things you have to do in order to find out the MonetDB API exposed to programmers by the MonetDB kernel (GDK). The parameters correspond to identifiers of BAT structures that you have to look them up and take the actual BAT. Cheers, Babis On Wed, Nov 20, 2013 at 12:40 PM, Alastair McKinley wrote:

Hi Babis,

Thanks again for the example steps to creating an aggregate.

Is there a typo in your code or is the C function supposed to take int* parameters?

I assumed it would be BATs like the MAL function signature?

Best regards and thanks,

Alastair ________________________________________ From: users-list on behalf of Charalampos Nikolaou Sent: 19 November 2013 17:32 To: Communication channel for MonetDB users Subject: Re: User Defined Aggregations in MonetDB?

This involves actually two steps.

1) SQL to MAL connection Example: CREATE AGGREGATE myagg (b INTEGER) RETURNS INTEGER EXTERNAL NAME mymodule.meagg;

2) MAL to C connection module mymodule;

command meagg(b:bat[:oid,:int], e:bat[:oid,:int]) :bat[:oid,:int] address meagg_c_implementation comment "Meagg mal aggregate";

str meagg_c(int *retid, int *bid, int *eid) { /* C code here */ }

The code is quite self-explanatory I think.

Hope that helps, Babis

On Tue, Nov 19, 2013 at 7:16 PM, Alastair McKinley wrote:

...

Hi Babis,

Thanks for your guidance that is very useful indeed!

I am not entirely clear on how a specific SUM aggregate query maps to a particular MAL signature/C function in aggr.mal.

For example, if I had

CREATE TABLE T ( int a, float b, float c );

SELECT a,SUM(b+c) FROM T GROUP BY a;

What MAL function signature would this result in?

Best regards and thanks,

Alastair ________________________________________ From: users-list on behalf of Charalampos Nikolaou Sent: 19 November 2013 14:15 To: Communication channel for MonetDB users Subject: Re: User Defined Aggregations in MonetDB?

Hi Alastair,

sure you can do that. You can have a look at the following files:

http://dev.monetdb.org/hg/MonetDB/file/af39d1a659f6/monetdb5/modules/kernel/... http://dev.monetdb.org/hg/MonetDB/file/af39d1a659f6/monetdb5/modules/kernel/... http://dev.monetdb.org/hg/MonetDB/file/af39d1a659f6/gdk/gdk_aggr.c

This article should be helpful and informative as well to you that explains how aggregates and grouping works inside MonetDB: http://www.monetdb.org/content/internal-changes-feb2013-release

Regards, Babis

On Tue, Nov 19, 2013 at 3:42 PM, Alastair McKinley wrote:

...

Dear all,

I was wondering if it is possible to build a User Defined Aggregation in MonetDB.

For example, rather than do SUM(myfunction(a,b)) I would like to do MYAGG(a,b) where MYAGG internally holds a small buffer of a and b values so that they can be calculated in a batch fashion with a high performance batch implementation of the function.

Could MYAGG be implemented in C?

Best regards,

Alastair

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