Re: MonetDB and cpu resources management

Thanks Robin. The problem with this is that the result I get is not correct. I don't know why but it is not equivalent to this: SELECT MIN(o_id) FROM (SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333) AS s; Here 's how managed to make it work (and seems to have better execution time): CREATE LOCAL TEMPORARY TABLE latestorders AS SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333 WITH DATA ON COMMIT PRESERVE ROWS; DECLARE min_o_id int; SET min_o_id = (SELECT MIN(o_id) FROM latestorders); SELECT i_id, i_title, a_fname, a_lname FROM item, author, order_line WHERE ol_o_id > min_o_id 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; Embedding the query to the WHERE clause to avoid the intermediate variable doesn't work. I simply don't get any response (result or error) from the system. On Wed, Jul 2, 2014 at 9:17 AM, Robin Cijvat < robin.cijvat@monetdbsolutions.com> wrote:

In my previous query, I forgot to give the biggest subquery an alias. So the query will become something like this:

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 ) sub2;

On 02-07-14 09:15, Robin Cijvat wrote:

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 wrote:

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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 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

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