July 2014 - users-list

Developing a C-based UDF
by Dennis Pallett 18 Jul '14

18 Jul '14

Hi all, I'm developing a C-based user defined function at the moment (actually porting an existing Postgres extension) and I was wondering what kinds of tools I should use for this and how I should actually do the development. At the moment I'm using a simple text editor to edit the relevant files (i.e. the c and mal files) and then completely re-compile MonetDB to test my changes. I'm not entirely happy about this workflow though, so is there an easier way? Perhaps with Visual Studio (I'… [View More]

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python3-monetdb cursor.scroll questions
by Chris Richards 16 Jul '14

16 Jul '14

Howdy. I've recently started using monetdb and was testing out the python3-monetdb module with the 'quick start' voc dataset. I'm not grokking the purpose of cursor.scroll() if it's working as intended. I am getting weird (to me) results, which I'm including below. Running 11.17.17-20140514 of the server, client, and python module under Ubuntu 14.04 LTS. My example starts at this point in the quick start guide (but in python): sql>SELECT type, COUNT(*) AS total I loaded this snippet into … [View More]the python3 interpreter: from monetdb import sql def p(c): print('.rowcnt={}, .__offset={}, .rownumber={}'.format ( c.rowcount, c._Cursor__offset, c.rownumber)) print ('.__rows={}'.format (c._Cursor__rows)) db = sql.connect(database='voc', user='voc', password='voc') cursor = db.cursor() # Set the arraysize small so it traverses result sets, # though it doesn't matter for the problem I'm seeing. cursor.arraysize = 2 cursor.execute("SELECT type, COUNT(*) AS total FROM onboard_people GROUP BY type ORDER BY type;") Then proceeded with this interactive session. Consecutive fetchone()'s seem to work properly; it traverses to the second result set. Where I get confused is when I .scroll(): >>> p(cursor) .rowcnt=6, .__offset=0, .rownumber=0 .__rows=[('craftsmen', 2349), ('impotenten', 938)] >>> cursor.fetchone() ('craftsmen', 2349) >>> p(cursor) .rowcnt=6, .__offset=0, .rownumber=1 .__rows=[('craftsmen', 2349), ('impotenten', 938)] >>> cursor.fetchone() ('impotenten', 938) >>> p(cursor) .rowcnt=6, .__offset=0, .rownumber=2 .__rows=[('craftsmen', 2349), ('impotenten', 938)] >>> cursor.fetchone() ('passengers', 2813) >>> p(cursor) .rowcnt=6, .__offset=2, .rownumber=3 .__rows=[('passengers', 2813), ('seafarers', 4468)] # Here's where I scroll back to the beginning. The # offset changes, but the rownumber doesn't. >>> cursor.scroll (0, mode='absolute') >>> p(cursor) .rowcnt=6, .__offset=0, .rownumber=3 .__rows=[('craftsmen', 2349), ('impotenten', 938), ('passengers', 2813), ('seafarers', 4468), ('soldiers', 4177)] # My expectation was that this would be ('craftsmen', 2349), # but it continues as if I didn't scroll. >>> cursor.fetchone() ('seafarers', 4468) # I try to back to the last item with no luck, it instead # marches forward to the next item as if I didn't scroll. >>> cursor.scroll (-1, mode='relative') >>> p(cursor) .rowcnt=6, .__offset=3, .rownumber=4 .__rows=[('seafarers', 4468), ('soldiers', 4177), ('total', 2467)] >>> cursor.fetchone() ('soldiers', 4177) Am I using the .scroll() wrong? Is this a bug? Thanks, Chris [View Less]

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Large query taking a long time
by Dennis Pallett 16 Jul '14

16 Jul '14

Hi all, I'm executing a very large query with MonetDB and it takes very long before the result is calculated (e.g. several minutes) whereas PostgreSQL does it in less than 100 ms. The query itself is a very simple select + sum query but the WHERE condition has more than a thousand equality tests on the primary key (ckey) of the table. It basically looks like this: SELECT sum(countAggr) FROM sys.london_hav_neogeo_pa WHERE ckey=16947611436 OR ckey=16947611437 OR ckey=16947611438 OR ckey=… [View More]

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TMP space deallocation
by Radovan Bičiště 08 Jul '14

08 Jul '14

Hi, My database started consuming disk space. Here is how: 1. run procedure. 2. procedure fails with server crash due to insufficient disk space. It eats up all the space and crash. 3. restart the database but the disk space remain allocated. All changes by the procedure are rolled back. There are inserts but not that many to eat up 10 GB of space. When I check sys.storage, it does not show any large table. My guess is that it allocates temporary space and it does not deallocate it after … [View More]

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MonetDB and cpu resources management
by Dimitris Karampinas 03 Jul '14

03 Jul '14

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 … [View More]

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