Hi Stefan,

Thank you very much for your suggestions. They are very helpful.

I am also trying to understand the hashjoin() implementation in gdk/gdk_join.c. I am aware of the classical *multi-pass partitioned hash join* as described in the literature:

[1] Main memory hash joins on multi-core CPUs: tuning to the underlying hardware. Cagri Balkesen et al. ICDE13

[2] Optimizing main-memory join on modern hardware. Stefan Manegold et al. TKDE (2002)

I was trying to follow the idea in these papers to understand the implementation of hash join in MonetDB but failed. Do you have any suggestions? Are there any other papers/documents I can refer to? Thanks.

Best regards,

XU Wenjian

>Hi Wenjian,

>you might want to consider studying the logical (relational) >and physical (MAL) plans, or debug your SQL queries; for >details see
>https://www.monetdb.org/Documentation/Manuals/SQLreference/Runtime

>You might also want to consider using the MAL debugger >directly; cf.,
>https://www.monetdb.org/Documentation/Manuals/MonetDB/debugger

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

>Best,
>Stefan

----- On Jul 8, 2015, at 11:42 AM, Xu,Wenjian zeroxwj at gmail.com 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
>> 
>> 
>>