BaseX-Talk October 2019

basex-talk@mailman.uni-konstanz.de

18 participants
28 discussions

Optimization issue?
by Johannes Echterhoff 25 Oct '19

25 Oct '19

Hello, I'm experiencing some strange behavior when executing the following query in the BaseX 9.2.4 GUI (nevermind the awkward query structure - that is just to be able to inspect the results of the individual evaluation steps): let $t := <x>200.0000</x> let $num := number($t) let $gt5000 := $num gt 5000 let $ltMinus5000 := $num lt -5000 return $gt5000 or $ltMinus5000 The result is true, although it should be false. The compilation and optimization logs for this query in the GUI tell us the following: ---------- Compiling: - rewrite > comparison to range comparison: ($num_1 > 5000) -> ($num_1 >= 5000.000000000001) - rewrite 'gt' comparison to range comparison: ($num_1 gt 5000) -> ($num_1 >= 5000.000000000001) - pre-evaluate unary expression to xs:integer item: -5000 - rewrite < comparison to range comparison: ($num_1 < -5000) -> ($num_1 <= -5000.000000000001) - rewrite 'lt' comparison to range comparison: ($num_1 lt -5000) -> ($num_1 <= -5000.000000000001) - inline $gt5000_2 - inline $ltMinus5000_3 - simplify or: (true()) - pre-evaluate or to xs:boolean item: (true()) -> true() - remove unused variable $num_1 - remove unused variable $t_0 - simplify FLWOR expression: true() Optimized Query: true() ---------- When the return statement is changed to "return ($num,$gt5000,$ltMinus5000,$gt5000 or $ltMinus5000)" then the result of the boolean operation (last element of the result sequence) is false, as expected. The GUI log then is: ---------- Compiling: - rewrite > comparison to range comparison: ($num_1 > 5000) -> ($num_1 >= 5000.000000000001) - rewrite 'gt' comparison to range comparison: ($num_1 gt 5000) -> ($num_1 >= 5000.000000000001) - pre-evaluate unary expression to xs:integer item: -5000 - rewrite < comparison to range comparison: ($num_1 < -5000) -> ($num_1 <= -5000.000000000001) - rewrite 'lt' comparison to range comparison: ($num_1 lt -5000) -> ($num_1 <= -5000.000000000001) Optimized Query: let $t_0 := element x { ("200.0000") } let $num_1 := number($t_0) let $gt5000_2 := ($num_1 >= 5000.000000000001) let $ltMinus5000_3 := ($num_1 <= -5000.000000000001) return ($num_1, $gt5000_2, $ltMinus5000_3, ($gt5000_2 or $ltMinus5000_3)) ---------- Am I missing something, or could this be a bug in BaseX 9.2.4? With BaseX 9.0.2, both queries (with the different return statements) returned the expected value false for the boolean operation. Best regards, Johannes

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Question about WITHDB option
by France Baril 24 Oct '19

24 Oct '19

I am looking at the documentation for WITHDB and I want to ask for further explanation 'If db:open is consistently used to access documents', does it means as opposed to having a DEFAULTDB or does it mean that we use db:open but not local queries on the document obtained (example below), or since there is a notion of lock, do you mean db:open as opposed to db:add or db:replace? In short, I lack context to interpret the explanation. let $current-doc := db:open($lang)/*[@id=x] (: Query document further without db:opened :) let $avaliable-sections := $current-doc/descendant::*[name()=''section][@status !='archived'] >From the documentation: WITHDB Introduced with Version 9.3. *Signature* WITHDB *Default* true *Summary* By default, URIs specified in the fn:doc <http://docs.basex.org/wiki/Databases#XML_Documents> and fn:collection <http://docs.basex.org/wiki/Databases#XML_Documents> functions will also be resolved against existing databases. If db:open <http://docs.basex.org/wiki/Database_Module#db:open> is consistently used to access database documents, it is recommendable to disable this option: - Access to local and external resources will be faster, as the database lookup will be skipped. - No locks will be created by the two functions (see limitations of database locking <http://docs.basex.org/wiki/Transaction_Management#Limitations> for more details). -- France Baril Architecte documentaire / Documentation architect france.baril(a)architextus.com

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catalog.xml - xsd - urn
by SW-Service 22 Oct '19

22 Oct '19

Good day, Where is the catalog.xml file stored? I want to validate xml files against XSD, but the xsd is referenced via an urn. thank you very much Guten Tag, Wo wird die catalog.xml Datei abgelegt? Ich möchte xml-Dateien gegen XSD validieren, aber die XSD wird über einen urn referenziert. Herzlichen Dank <xdomea:Aussonderung.Aussonderung.0503 xmlns:xdomea="urn:xoev-de:xdomea:schema:2.3.0">

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Re: [basex-talk] Backups
by Christian Grün 21 Oct '19

21 Oct '19

Hi Christoph, > db_alter() has not changed. It alters the name of the database but the corresponding backups stay unchanged. I combine it with db:drop-backup() That’s true: db:alter() will only rename databases. This has been a deliberate design choice (in analogy with db:drop, a user might want to treat backups differently than the currently active instance); but I think we should add an additional db:alter-backup function. I have just created an issue for that [1]; Thanks for the observation. > I copied the old data, restxq etc. into the new structure. > … > In both cases I lost my users. How can I upgrade without loosing them? Users are stored in the data directory in the users.xml file. Did you copy this file as well? Maybe the BaseX server was still running while you were copying the files? For databases, this shouldn’t matter (database are dynamically accessed), but the users.xml file will only be parsed at startup time. Best, Christian [1] https://github.com/BaseXdb/basex/issues/1742 On Mon, Oct 21, 2019 at 1:47 PM Christoph Gaukel <christoph.gaukel(a)gmx.de> wrote: > > Hi Christian, > > thank you for your answer. I upgraded from 9.1.2 to 9.2.4 and indeed: > > the output of db:backups('test_balance_tmp') changed from: > <backup database="test_balance_tmp" date="2019-10-18T00:05:50" size="2230">test_balance_tmp-2019-10-18-00-05-50</backup> > to: > <backup database="test_balance_tmp" date="2019-10-17T22:05:50Z" size="2230">test_balance_tmp-2019-10-18-00-05-50</backup> > > The same with db:drop(), now it deletes the database but not the backups. > > db_alter() has not changed. It alters the name of the database but the corresponding backups stay unchanged. I combine it with db:drop-backup() > > > From doing the upgrade, I got a new question. I have done two trials: > > I copied the old data, restxq etc. into the new structure. > I copied BaseX.jar and basex/lib into the old structure > > In both cases I lost my users. How can I upgrade without loosing them? > > > Thanks, > > Christoph > > Am 18.10.19 um 10:25 schrieb Christian Grün: > > Hi Christoph, > > Welcome back to the list. > > db:drop deletes both, the database and the corresponding backups > > The function should only delete database and preserve backups. For > deleting backups, db:drop-backup can be used. Maybe there was a bug in > an older version of BaseX? > > db:info($db)/resourceproperties/inputdate is a UTC dateTime with a time zone offset > db:backups($db)/@date is a local dateTime without a time zone offset > > Same here: Both returned timezones should be a UTC dateTime with the Z > time offset. > > Maybe you need to switch to the latest version of BaseX? > Feel free to give us an update if the problems persist with BaseX 9.x. > > Hope this helps, > Christian >

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HTTP request
by Giuseppe G. A. Celano 18 Oct '19

18 Oct '19

Hi, I have a curl request of the kind curl --data "something" http://something <http://something/> which I would like to perform using the HTTP module, but I cannot specify the data argument in the query. Any help? The following does not work: http:send-request(<http:request method="post"></http:request>, 'http://something' , "something" ) Best, Giuseppe

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simplest possible FLOWR specifying a database
by thufir 12 Oct '19

12 Oct '19

these FLWOR .xq files work as is: let $db := db:open("com.w3schools.books") for $x in $db/bookstore return $x or <new_catalog>{ let $db := db:open("com.w3schools.books") for $x in $db/bookstore/book return <new_book>{$x/title,$x/author}</new_book> }</new_catalog> Probably a silly question, but, rather than, as in the first query, using $x can I not somehow specify just "/"? thanks, Thufir

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what do with treasury data?
by thufir 11 Oct '19

11 Oct '19

I randomly came across the data at: https://www.treasurydirect.gov/xml/ which is all well and good, but what might be a good starter project with this data? Perhaps join it with other data? But what other data? Not even sure what this data, except that there's mention of announcements and auctions. thanks, Thufir

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Migrating ~ 3M record db from BaseX to PostgreSQL results in OOM
by first name last name 08 Oct '19

08 Oct '19

Hello, This is essentially part2 of trying to index large amounts of web data. To summarize what happened before: The initial discussion started here [1], Christian suggested some options, I dove into each of them, I realized that doing this on a low-memory system is harder than I initially thought. At Christian's suggestion, I tried to split the big db into smaller dbs and came up with a rudimentary sharding mechanism [3]. All attempts to full-text 30GB of data in BaseX, for me, resulted in OOM (do take into consideration that I only have 3.1GB of memory to allocate for BaseX). Where to? I decided to look more into what Christian said in [2] about option 2, and to pick the exact values that I want, and to transfer them to PostgreSQL (after transferring, a GiST index would have to be built there, to allow full-text searches; PostgreSQL is picked because it uses an in-memory buffer for all large operations, and several files on disk, and if it needs to combine results that exceed the available memory, it goes to disk, but at all times it never exceeds the given amount of memory). Variant 1 (see attached script pg-import.sh) All good. So, I basically started writing XQuery that would do the following: - Open up a JDBC connection to PostgreSQL - Get me all text content from each thread page of the forum, and the db it belonged to - Create a prepared statement for one such thread page, populate the prepared statement, and execute it This ended up in OOM after around 250k records. So just to be clear, 250k lines were rows in PostgreSQL, which is nice but eventually it ended up in OOM. (Perhaps it has to do with how the GC works in Java .. I don't know) Variant 2 (see attached script pg-import2.sh) I did something similar to the above: - Open up a JDBC connection to PostgreSQL - Get all posts and for each post get the author, the date, the message content, the post id, the BaseX db name (cause we're going over all shards, and each shard is a BaseX db) - Create a prepared statement for each post with the data mentioned above, and execute it This also ended up in OOM after around 340k records (my approximation would be that there were around 3M posts in the data). To summarize, I'm tempted to believe that there might be a leak in the BaseX implementation of XQuery. I will provide in the following, the relevant versions of the software used: - BaseX 9.2.4 - java version "1.8.0_151" Java(TM) SE Runtime Environment (build 1.8.0_151-b12) Java HotSpot(TM) 64-Bit Server VM (build 25.151-b12, mixed mode) - the JVM memory param value was -Xmx3100m I would be interested to know your thoughts Thanks, Stefan [1] https://mailman.uni-konstanz.de/pipermail/basex-talk/2019-September/014715.… [2] https://mailman.uni-konstanz.de/pipermail/basex-talk/2019-October/014727.ht… [3] https://mailman.uni-konstanz.de/pipermail/basex-talk/2019-October/014729.ht…

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Want event, not polling....
by Peter Villadsen 07 Oct '19

07 Oct '19

Hello, I am using a client written in C#. For the sake of this discussion, imagine the app being discussed as an app just like the Java GUI app that ships with BaseX: You can basically author Xquery snippets and send them for execution by the server. We regularly have queries that tend to run for a long time, and it would be an advantage for the user to be able to cancel these long running jobs, just like he can in the GUI app. However, I am not sure how to do this; I can imagine two solutions: 1. I see that jobs that are submitted normally to the server end up as jobs, just like the ones that are submitted with jobs:eval(query): I can stop that job with jobs:stop(jobId) on another session if the jobId is known. You would need a separate session that fetches the running jobs and gets the current one (recognizing it by creating a cookie in a comment in the query) with jobs:list-details(), then getting the jobId and then calling jobs:stop(jobId). It is possible I guess, but very heavy handed. 2. The other option is just as bad: submit the query through jobs:eval(query), getting the jobId and then poll for it to finish; more polling which will not scale with many users and will not provide the quick feedback we want. I see some traces of an eventing mechanism that was deprecated (or at least no longer included in the client). That is what I would ideally have (ignoring bindings etc): Query q = new Query("1 to 10" , new Guid()); q.Ended += MyTerminationHandler(); // C# syntax for adding an event handler for termination q.Interrupted += MyInterruptedHandler(); await q.execute(); // Called when the query has terminated with a result void MyTerminationHandler(Guid g, string result) { ... update UI ... } // Called when the query has terminated with a result void MyInterruptedHandler (Guid g) { ... update UI ... } How do I do this without the polling, being able to pass massive results and queries back and forth? Best Regards Peter Villadsen Principal Architect Microsoft Business Applications Group

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how to specify a database in a.xq FLOWR query?
by thufir 07 Oct '19

07 Oct '19

how do I specify a database for a .xq file to use? a simple FLOWR: thufir@dur:~/basex/w3$ thufir@dur:~/basex/w3$ basex titles.xq [warning] /usr/bin/basex: Unable to locate /usr/share/java/jing.jar in /usr/share/java <title lang="en">Learning XML</title> <title lang="en">XQuery Kick Start</title>thufir@dur:~/basex/w3$ thufir@dur:~/basex/w3$ thufir@dur:~/basex/w3$ cat titles.xq for $x in doc("books.xml")/bookstore/book where $x/price>30 order by $x/title return $x/title thufir@dur:~/basex/w3$ (from w3schools) thanks, Thufir

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BaseX-Talk October 2019