November 2017 - users-list

UDF function with >3 parameters cannot benefit from using PYTHON_MAP
by Hanfeng Chen 15 Nov '17

15 Nov '17

Hi, I created a table with 9 columns and passed 6 columns from the table to a UDF. This UDF is fully vectorizable. However, we found only single thread was used during the execution. Then, we came to think about what the problem behind and we created the two simple functions python_min_map_3 and python_min_map_4 which takes 3 and 4 parameters separately. The MonetDB Linux version we used was July 2017. If PYTHON_MAP is enabled, it would return the results of each segment processed by parallel code. The number of results depends on how many threads are used. Otherwise, a single value should be returned (e.g. because of numpy.min). The result is - python_min_map_3 returns a couple of numbers - python_min_map_4 returns a single number Even when we increased the number of the arguments, a single number was always returned. Is it a restriction in using PYTHON_MAP when the number of arguments should be no more than 3? Here is our example code below. CREATE FUNCTION python_min_map_3(x0 FLOAT, x1 FLOAT, x2 FLOAT) RETURNS FLOAT LANGUAGE PYTHON_MAP { return numpy.min(x0) }; select python_min_map_3(x0, x1, x2) from table_0; CREATE FUNCTION python_min_map_4(x0 FLOAT, x1 FLOAT, x2 FLOAT, x3 FLOAT) RETURNS FLOAT LANGUAGE PYTHON_MAP { return numpy.min(x0) }; select python_min_map_4(x0, x1, x2,x3) from table_0; NumPy in MonetDB reference: https://www.monetdb.org/blog/embedded-pythonnumpy-monetdb Best regards, Hanfeng Chen

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read BLOB column on tail heap and loop over rows
by Anton Kravchenko 13 Nov '17

13 Nov '17

I wonder how one would read BLOB column and loop over its rows? BAT *b = table_funcs.full_column(m->session->tr, blob_col_name); //blob *readblobrows = (blob*) b->T.heap.base; //unsigned char *readblobrows = (unsigned char*) b->T.heap.base; p.s. For INT column it would be go like this: int * readintrows = (int *) b->T.heap.base; for (irow=0; irow < nrow; irow++) { intvalue = *readintrows++; } Thanks, Anton

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Querying JSON arrays
by Brian Ploetz 09 Nov '17

09 Nov '17

Hi, Suppose I have a table with a "tags" column that is of the JSON datatype ( https://www.monetdb.org/Documentation/Manuals/SQLreference/Types/JSON). The column will contain a JSON array of Strings. For example: ["foo","bar","baz"] Is it possible to query for rows that contain a specific value in the tags array? For example, if I wanted to find all of the rows where tags contains "foo", my query would look something like: select count(*) from my_table where tags ???? 'foo'; But it's not clear to me what ???? should be (or if it's even possible) based on the JSON documentation above. Thanks in advance. BP

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large virtual memory spike on BLOB column select
by Anton Kravchenko 09 Nov '17

09 Nov '17

I am using MonetDB v11.27.9 on cent7. 1) 'select v_blob from blob_table' produces a virtual memory spike ~800Gb [using a 'limit' reproduces virtual memory spike too] >From 'select * from storage()' it looks a blob column size is ~25Gb. 2) And 'create table new_blob_table as (select v_blob from blob_table) with data;' produces only ~50Gb of virtual memory. 3) Also for a table with non-blob column both 'select * from nonblob_table' and 'create new_nonblobtable as (select * from nonblob_table) with data;' produce the ~same virtual memory consumption. p.s. Here are steps to reproduce this issue # to generate date by using Python hex_blob='47'*2000 hex_blob_chunk=(hex_blob+'\n')*1000 f=open('blob_data.txt','w') for irow in range(10000): f.write(hex_blob_chunk) f.close() # to load data into Monet blob_table create table blob_table(v_blob blob); COPY 10000000 RECORDS INTO blob_table FROM '/home/blob_data.txt' using delimiters ',','\n' NULL AS '' LOCKED; # to produce virtual memory spike of ~800GB select * from blob_table limit 50000; # to produce virtual memory of ~50Gb create table new_blob_table as (select * from blob_table) with data; Thanks, Anton

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Problems creating json files with more than 10^3 table entries
by Giacomo Bergami 08 Nov '17

08 Nov '17

I am using MonetDB-11.27.9 on ubuntu 17.04. The client was compiled from the source code. I am trying to run the following query on your database select distinct T.src as author, T1.src as coauthor, json.tojsonarray(T1.dst) as papers from edges1000 as T, edges1000 as T1 where T.dst = T1.dst AND T.src <> T1.src group by T.src, T1.src ; When I run this query over a table with at most 10^4 entries, the mclient client quits. If I try to execute the same qury via JDBC, I receive an error that tells me "maybe mserver closed unexpectedly". On the other hand, the server is still alive and responsive if I afterwards run the query either oover mclient or JDBC over a table having less data (edges10). Is that a problem of memory allocation ? Is there a way to solve this issue? I'm using the default configuration, and compiled the source code using "autoreconf -if" first. Thanks in advance for your support, Bergami G

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latest version question
by Lynn Carol Johnson 02 Nov '17

02 Nov '17

Hello monetdb team – We upgraded this afternoon to the latest version of monetdb (Jul2017-SP2). When testing access for my lab, I noticed the general login could no longer perform the command: \d <table_name> The errors were related to missing group access to sys.objects, sys.keys and sys.idxs. When, as monetdb admin, I granted “select” on these tables, the “\d <table_name>” command then worked. Is this something new, or does it indicate a problem with the db ? It was not necessary to grant general users permission to these system tables previously. Thanks - Lynn

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