Hi Dimitris (sorry for the typo),

@Bryan: Thanks for mentioning that, I was not aware of the windowing functionality :) I tried it out, and for me it seems to work. So for your simple example, you would do the following rewrite:

SELECT MIN(o_id) FROM (SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333) AS s;

-->

SELECT MIN(o_id)
FROM (
    SELECT o_id
    FROM (
        SELECT row_number() over (ORDER BY o_date DESC) as row, o_id
        FROM orders
    ) AS sub
    WHERE sub.row <= 3333
);

I had to add an extra subquery, since the WHERE clause in the part where you select the row_number(), is not aware of the identifier 'row' yet.

I would advise using this over the temporary tables, since a) it is much simpler to write and b) you don't have to worry about having to manage intermediate results yourself.

I hope you can extend this example to your original query.

Best,
Robin





On 01-07-14 20:43, Bryan Senseman wrote:

Actually, I think you can trick it depending on your version of MonetDB and use the RANK windowing function inside the innermost subquery and then use a standard where clause on the appropriate outside snippet to limit the returned rows.

 

Bryan

From: users-list [mailto:users-list-bounces+monetdb=openbi.com@monetdb.org] On Behalf Of Dimitris Karampinas
Sent: Tuesday, July 01, 2014 2:27 PM
To: Communication channel for MonetDB users
Subject: Re: MonetDB and cpu resources management

 

DimitrIs :)

 

I thought of temporary tables before posting but a) I was skeptic about the extra overhead b) my first try to use them failed...

 

For the aforementioned query I do the following:

 

CREATE LOCAL TEMPORARY TABLE toporders AS SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333 WITH DATA ON COMMIT PRESERVE ROWS;

 

SELECT i_id, i_title, a_fname, a_lname

FROM item, author, order_line

WHERE ol_o_id > (SELECT MIN(o_id) FROM toporders)

            AND i_id = ol_i_id AND i_a_id = a_id AND i_subject = 'HOME'

GROUP BY i_id, i_title, a_fname, a_lname

ORDER BY SUM(ol_qty) DESC

LIMIT 50;

 

 

The command prompt returns but there is no result, neither any syntax/whatever error response.

 

Cheers!

Dimitris

 

On Tue, Jul 1, 2014 at 5:29 PM, Robin Cijvat <robin.cijvat@monetdbsolutions.com> wrote:

Hi Dimitras.

MonetDB indeed does not support LIMIT in subqueries. A simple workaround is just storing the result of the subquery in a temporary table (https://www.monetdb.org/Documentation/Manuals/SQLreference/Tables) and then referring to this temporary table in the main query.

Maybe not an ideal solution, but it will work.

Regards,
Robin Cijvat



On 01-07-14 16:53, Dimitris Karampinas wrote:

Hi,

 

Thanks for your answers. I hope stethoscope will help.

 

One more question, not relevant to the previous one but I hope it's OK not to open a new thread.

 

I'm trying to run the BestSellers query from TPC-W on MonetDB.

The query works as follows:

- Take the smallest order id from the most recent 3333 orders.

- Then take all order lines more recent than that, sum their quantities by item, and display the top 50 by total quantity.

 

Here is some SQL code for this:

 

SELECT i_id, 

       i_title, 

       a_fname, 

       a_lname 

FROM   item, 

       author, 

       order_line 

WHERE  ol_o_id > (SELECT Min(o_id) 

                  FROM   (SELECT o_id 

                          FROM   orders 

                          ORDER  BY o_date DESC 

                          LIMIT  3333) s) 

       AND i_id = ol_i_id 

       AND i_a_id = a_id 

       AND i_subject = 'HOME' 

GROUP  BY i_id, 

          i_title, 

          a_fname, 

          a_lname 

ORDER  BY Sum(ol_qty) DESC 

LIMIT  50;

 

 

I'm having trouble in expressing the nested sub-query:

 

SELECT MIN(o_id) FROM (SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333) AS s;

 

Searching in previous mails in this list, I found out that MonetDB does not support ORDER BY or LIMIT in subqueries.

Is there any workaround ?

 

 

Cheers!

Dimitris

 

On Mon, Jun 30, 2014 at 2:24 PM, Sjoerd Mullender <sjoerd@acm.org> wrote:

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Hash: SHA1


On 2014-06-30 11:53, Dimitris Karampinas wrote:
> Hi,
>
> I'm trying to set the maximum number of cores using gdk_nr_threads
> parameter but it doesn't seem to work for me. I've tried "variants"
> of this command: monetdbd set gdk_nr_threads=4 start /my/dbfarm but
> it seems like gdk_nr_threads is not a supported property.
>
> Additionally to this, I would like to ask how does MonetDB handle
> concurrent user sessions and the available cpu resources ? The
> manual says there is support for "inter- and intra- parallelism".
> Can someone roughly explain me what to expect or give me a pointer
> to the code that is responsible for resource management ?
>
> Cheers! Dimitris

Read the manual: man monetdb.  It will tell you about the
nthreads=number command.


- --
Sjoerd Mullender
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