Interaction of operators in the kernel.

Stefan Manegold Stefan.Manegold at
Wed Jul 8 13:18:21 CEST 2015

Hi Wenjian,

you might want to consider studying the logical (relational) and
physical (MAL) plans, or debug your SQL queries; for details see

You might also want to consider using the MAL debugger directly; cf.,

Also, a combination of mserver5's --trace and --gdk_debug=2097152 ("ALGOMASK")
might be useful.


----- On Jul 8, 2015, at 11:42 AM, Xu,Wenjian zeroxwj at wrote:

> Hi,
> My objective is to investigate that, given an SPJ query, how are BATs
> *physically* processed (changed) among relational algebra operators (e.g.,
> select, join). I do not care about how query is translated into execution plan
> in MAL, what I care is the interaction of operators in the kernel (aka., gdk) .
> My current plan is to add some debug information in those operators (e.g.,
> functions in src/gdk_join.c, src/gdk_select.c) and re-compile the system. Then,
> I will pose an SPJ query (through console) and check the system log to see how
> those operators are invoked in sequence.
> But this method seems inefficient and I would like to ask if there are any
> alternatives, for example, is it possible to debug the system *step-by-step*
> given an input query (or its logical query plan).
> Thank you very much for any kind help.
> Best regards,
> Wenjian
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