February 2018 - users-list

[MonetDB-users] Books CDs
by CHARTS LICENSING 11 Aug '24

11 Aug '24

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Multi-column update based on joined table
by Lee Hachadoorian 11 Aug '24

11 Aug '24

I need to update multiple columns (~250) from one table to another based on a two-column key. In Postgres I would write this using the FROM clause, but since MonetDB doesn't support the FROM clause, I've successfully updated one column with: UPDATE census.acs2010_5yr SET b07401001 = ( SELECT CAST(b07401001 AS int) FROM acs2010_5yr.tmp_seq0001 WHERE acs2010_5yr.stusab = tmp_seq0001.stusab AND acs2010_5yr.logrecno = tmp_seq0001.logrecno ); My question is whether there is any benefit to writing a multiple column update into a single UPDATE statement: UPDATE target_table SET column1 = (SELECT column1 FROM source_table WHERE target_table.key = source_table.key), column2 = (SELECT column2 FROM source_table WHERE target_table.key = source_table.key), ..., columnN = (SELECT columnN FROM source_table WHERE target_table.key = source_table.key); On Postgres I believe the multi-column update using a table join would only have to do the sequential scan of each table once, but with the necessity of sub-selects in MonetDB, what is the backend doing? Is it already doing an index scan once for each row in the single column case, then doing it once for each row * column in the multi-column case? Best, --Lee -- Lee Hachadoorian Asst Professor of Geography, Dartmouth College http://freecity.commons.gc.cuny.edu/

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[MonetDB-users] XQuery API and XLink/XUpdate support
by Alexandra Mart�nez 27 Jun '24

27 Jun '24

Hello all, I was wondering if there is any documentation about the API for XQuery (i.e., how to write xqueries from a Java program). Also, I am interested in using some features of XLink and XUpdate on top of my XML database. Is support for any of these in progress? Thanks in advance, Alexandra ______________________________________________________ Click here to donate to the Hurricane Katrina relief effort. http://store.yahoo.com/redcross-donate3/

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[MonetDB-users] Proofreading your professional documents
by Richard Hounslow 24 Feb '24

24 Feb '24

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current_time() precision
by Roberto Cornacchia 28 Feb '18

28 Feb '18

sql>select current_time(); +-----------------------+ | L2 | +=======================+ | 17:05:10.000000+01:00 | +-----------------------+ 1 tuple (0.796ms) Is it expected that the result type's precision of current_time() is limited to seconds? Any way to get milliseconds?

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Monetdb hanging on query
by Manuel Pagliai 27 Feb '18

27 Feb '18

Hello, I am using Monetdb as the query engine of an application currently in development. I am connecting to monetdb via a jdbc connection. I can easily reproduce a scenario where monetdb gets stuck on a query, and never complete execution. Although reproducible, the issue is non deterministic, and it can occur while executing different queries, or not occur at all. When it happens I can see the thread stuck at I extracted the queries submitted to monetdb, and execute them via a standalone client (both the native client and a jdbc-based one) rather than our application, but I have been unable to reproduce the issue that way. I guess timing is important. The problem still occur even when queries are submitted sequentially and setting gdk_nr_threads=1 and sql_optimizer=sequential_pipe. The issue happens in Jul 2017-SP3 bugfix release (11.27.11), running on a Windows 7 machine. I have not tried 11.27.13, but by looking at the bug fixes I can't see anything relevant to this issue. Is there something that I can try, or a way to gather more information about what is happening ? I can share both the data, and the complete list of queries used during this scenario. Thanks, Best regards, *Manuel Pagliai* Visokio Ltd www.visokio.com +44 20 7351 4646 P.S. This is the stack-trace of the thread submitting the query when this happens: at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.socketRead(SocketInputStream.java:116) at java.net.SocketInputStream.read(SocketInputStream.java:171) at java.net.SocketInputStream.read(SocketInputStream.java:141) at java.io.BufferedInputStream.fill(BufferedInputStream.java:246) at java.io.BufferedInputStream.read1(BufferedInputStream.java:286) at java.io.BufferedInputStream.read(BufferedInputStream.java:345) - locked <0x00000000cae0b730> (a java.io.BufferedInputStream) at nl.cwi.monetdb.mcl.net.MapiSocket$BlockInputStream._read(Unknown Source) at nl.cwi.monetdb.mcl.net.MapiSocket$BlockInputStream.readBlock(Unknown Source) at nl.cwi.monetdb.mcl.net.MapiSocket$BlockInputStream.read(Unknown Source) at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284) at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326) at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178) - locked <0x00000000cae13810> (a java.io.InputStreamReader) at java.io.InputStreamReader.read(InputStreamReader.java:184) at java.io.BufferedReader.fill(BufferedReader.java:161) at java.io.BufferedReader.readLine(BufferedReader.java:324) - locked <0x00000000cae13810> (a java.io.InputStreamReader) at java.io.BufferedReader.readLine(BufferedReader.java:389) at nl.cwi.monetdb.mcl.io.BufferedMCLReader.readLine(Unknown Source) at nl.cwi.monetdb.mcl.io.BufferedMCLReader.waitForPrompt(Unknown Source) - locked <0x00000000cae137d8> (a nl.cwi.monetdb.mcl.io.BufferedMCLReader) at nl.cwi.monetdb.jdbc.MonetConnection$ResponseList.executeQuery(Unknown Source) - locked <0x00000000cae0b430> (a nl.cwi.monetdb.mcl.net.MapiSocket) at nl.cwi.monetdb.jdbc.MonetConnection$ResponseList.processQuery(Unknown Source) at nl.cwi.monetdb.jdbc.MonetStatement.internalExecute(Unknown Source) at nl.cwi.monetdb.jdbc.MonetStatement.execute(Unknown Source) at nl.cwi.monetdb.jdbc.MonetStatement.executeQuery(Unknown Source)

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MonetDB :: Alter statement to change datatype
by Sharma, Sreejith 22 Feb '18

22 Feb '18

All, Is it possible to change the datatype of a column in an existing table? With or without data? I saw the only way to change is to create a temporary column and swap if data is present. Is it true? Regards, Sreejith

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Re: Order indexes: used or not?
by Stefan Manegold 20 Feb '18

20 Feb '18

Hi Torsten, To start mserver5 manually on a database created by monetdb/monetdb, you need to use the same command line (-options) the monedtd use to start mserver5, in particular the valley option. You find the details in the merovingian.log in your dbfarm Best,Stefan -------- Original message --------From: Torsten Grust <torsten.grust(a)gmail.com> Date: 2/20/18 17:08 (GMT+01:00) To: Lefteris <lsidir(a)gmail.com> Cc: Communication channel for MonetDB users <users-list(a)monetdb.org> Subject: Re: Order indexes: used or not? Hi Lefteris, that's very interesting. Thanks! I was about to experiment with this here, but I stumbled. When you start a database via mserver5 directly (instead of using monetdbd which, as I understand, is the recommend method), does the method of authentication change? I fail to login to my scratch database: $  mserver5 --dbpath=<path>/scratch # MonetDB 5 server v11.27.13 "Jul2017-SP4" # Serving database 'scratch', using 4 threads # [...] # MonetDB/SQL module loaded > [switch to other terminal] $ mclient -d scratch -u monetdb password: <supply password "monetdb"> InvalidCredentialsException:checkCredentials:invalid credentials for user 'monetdb' Whereas the login works just fine below: $ monetdbd start <path> $ mclient -d scratch -u monetdb password: <supply password "monetdb"> Welcome to mclient, the MonetDB/SQL interactive terminal (Jul2017-SP4) Database: MonetDB v11.27.13 (Jul2017-SP4), 'mapi:monetdb://closure:50000/scratch' [...] sql> I must be doing something stupid. Cheers, —Torsten On Tue, Feb 20, 2018 at 3:40 PM Lefteris <lsidir(a)gmail.com> wrote: Hi Torsten, the reason why you don't see anything in the EXPLAIN statement is that the use of an index is decided at runtime by the respective operator. The algebra.sort code will have an if statement that determines at query evaluation time if there is a usable ordered index and use it. The best way (for now) to see if the index is used or not is to start the mserver5 with the --algorithms flag. This flag will produce alot of output on the runtime decissions. For your example, I get the following output: #BATproject(l=tmp_523#3-sorted-key,r=tmp_433#3[int]-revsorted-key) #BATproject(l=tmp_523,r=tmp_433)=tmp_323#3-revsorted-key #BATcheckorderidx: reusing persisted orderidx 283 #BATproject(l=tmp_322#3-key,r=tmp_323#3[int]-revsorted-key) #BATproject(l=tmp_322,r=tmp_323)=tmp_417#3-key 11us #BATgroup(b=tmp_417#3[int],s=NULL#0,g=NULL#0,e=NULL#0,h=NULL#0,subsorted=1): trivial case: 1 element per group #BATprojectchain with 3 (2) BATs, size 3, type int #BATproject(l=tmp_322#3-key,r=tmp_323#3[int]-revsorted-key) #BATproject(l=tmp_322,r=tmp_323)=tmp_523#3-key 9us And the third line says "BATcheckorderidx: reusing persisted orderidx 283" which is an indication that MonetDB has found the index and is using it. As a side note, I think in this case it has also figured out that x is revsorted-key (aka unique reverse sorted) but I dont know which one wins over the other:) So in short, if you start mserver5 with --algorithms, redirect the console output in a file and search for BATcheckorderidx you will see if the ordered index is used. Please let us know if there are cases that ordered index should be used but it is not. lefteris On Fri, Feb 16, 2018 at 10:28 AM, Martin Kersten <martin.kersten(a)cwi.nl> wrote: > Hi > Same holds for ordered indices > > On 16/02/2018 10:27, Torsten Grust wrote: >> >> Hi Martin, >> >> thanks for the super-quick reply. You are talking of /imprints/ here but >> I assume that the same is true for /order indexes/ (these are separate >> concepts, right?). >> >> Best wishes, >> —Torsten >> >> >> On Fri, Feb 16, 2018 at 9:55 AM Martin Kersten <martin.kersten(a)cwi.nl >> <mailto:martin.kersten@cwi.nl>> wrote: >> >> Dear Torsten >> >> The use of an imprint is only part of the algebra.select >> implementation >> and depends on actual several properties. >> >> In this particular query, the SQL compiler when encountering an order >> by >> issues a sort statement, even if this is strictly not needed. That >> will be detected >> by the sort implementation. >> >> regards, Martin >> On 15/02/2018 23:31, Torsten Grust wrote: >> > Dear all, >> > >> > given a table definition and (explained) SQL query as follows: >> > >> > |CREATE TABLE foo (x INT,y INT); INSERT INTO foo VALUES (3,1), >> (2,2), (1,3); ALTER TABLE foo SET READ ONLY; CREATE ORDERED INDEX foo_x ON >> foo(x); EXPLAIN SELECT * FROM foo ORDER BY x; | >> > >> > In the |EXPLAIN| output, am I supposed to see that the order index >> is indeed used? I currently do see an |algebra.sort| operation, of course, >> but do not see any reference to the |foo_x| index. I had expected to find an >> |bat.getorderidx| operation in the >> > MAL program. >> > >> > Can anyone shed light on this? I'd be grateful. >> > >> > Cheers, >> > >> > —Torsten >> > >> > -- >> > | Prof. Dr. Torsten Grust >> > | Database Systems — Universität Tübingen (Germany) >> > | ✉︎ torsten.grust(a)uni-tuebingen.de >> <mailto:torsten.grust@uni-tuebingen.de> >> <mailto:torsten.grust@uni-tuebingen.de >> <mailto:torsten.grust@uni-tuebingen.de>> >> > | db.inf.uni-tuebingen.de <http://db.inf.uni-tuebingen.de> >> <http://db.inf.uni-tuebingen.de> >> > >> > >> > _______________________________________________ >> > users-list mailing list >> > users-list(a)monetdb.org <mailto:users-list@monetdb.org> >> > https://www.monetdb.org/mailman/listinfo/users-list >> > >> _______________________________________________ >> users-list mailing list >> users-list(a)monetdb.org <mailto:users-list@monetdb.org> >> https://www.monetdb.org/mailman/listinfo/users-list >> >> -- >> | Prof. Dr. Torsten Grust >> | Database Systems — Universität Tübingen (Germany) >> | ✉︎ torsten.grust(a)uni-tuebingen.de >> <mailto:torsten.grust@uni-tuebingen.de> >> | db.inf.uni-tuebingen.de <http://db.inf.uni-tuebingen.de> >> >> >> _______________________________________________ >> users-list mailing list >> users-list(a)monetdb.org >> https://www.monetdb.org/mailman/listinfo/users-list >> > _______________________________________________ > users-list mailing list > users-list(a)monetdb.org > https://www.monetdb.org/mailman/listinfo/users-list -- | Prof. Dr. Torsten Grust | Database Systems — Universität Tübingen (Germany)| ✉︎ torsten.grust(a)uni-tuebingen.de| db.inf.uni-tuebingen.de

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Order indexes: used or not?
by Torsten Grust 20 Feb '18

20 Feb '18

Dear all, given a table definition and (explained) SQL query as follows: CREATE TABLE foo (x INT,y INT); INSERT INTO foo VALUES (3,1), (2,2), (1,3); ALTER TABLE foo SET READ ONLY; CREATE ORDERED INDEX foo_x ON foo(x); EXPLAIN SELECT * FROM foo ORDER BY x; In the EXPLAIN output, am I supposed to see that the order index is indeed used? I currently do see an algebra.sort operation, of course, but do not see any reference to the foo_x index. I had expected to find an bat.getorderidx operation in the MAL program. Can anyone shed light on this? I'd be grateful. Cheers, —Torsten -- | Prof. Dr. Torsten Grust | Database Systems — Universität Tübingen (Germany) | ✉︎ torsten.grust(a)uni-tuebingen.de | db.inf.uni-tuebingen.de

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matrix manipulation
by Jiří Fejfar 20 Feb '18

20 Feb '18

Dear MonetDB users! I would like to do some simple calculations (matrix multiplication and inversion) with large matrices (cca 40k by 40k or more). We are using PostgreSQL & R but we are facing problems when matrix doesn't fit memory. My initial idea was to use SciQL, but probably it is not merged into MonetDB yet [1]? I am sending also short presentation [2] illustrating nature of our data and calculation (slide 6). Thank you for your suggestions! Jiří. [1] https://www.monetdb.org/pipermail/users-list/2014-May/007319.html [2] https://drive.google.com/open?id=1P4Nuo_YuqhNyxoBqQHeIw6WiXe28I8kE

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