BaseX-Talk August 2012

basex-talk@mailman.uni-konstanz.de

35 participants
42 discussions

motivation for using connection pools
by Godmar Back 11 Aug '12

11 Aug '12

Hi, Christian and I had a brief discussion regarding create db, session semantics and the use of connection pools on github [1]. He asked for real user feedback. I'll try to briefly describe what motivated us to use connection pools; I believe our experience may be indicative of that of others developing applications in which BaseX provides the database tier. Our application is an AJAX-based front-end that allows users to manage information stored in a BaseX database. When a user clicks on some part of the user interface, the resulting AJAX request may trigger one or more operations on a BaseX database. Typically between 1 and as many as 10. (Now part of these operations could perhaps be avoided through caching, but caching comes of course with its own problems since we have no easy way to keep multiple caches for the same BaseX instance coherent). These operations include queries, updates, creating/renaming databases, and the like. In this common situation, how would one manage access to BaseX? Option A. is to create a new TCP connection to BaseX for every single query,update, or command. That would involve 1-10 TCP connection setups, plus whatever (and however small) session setup costs BaseX has, per user event. As a ballpark number, if the BaseX server runs on a separate machine in our cluster, as is good practice, this can involve many milliseconds of overhead, which adds to the overall latency of our application. (I note that one source of overhead is the need to serialize our in-memory DOM objects for each query, and to parse the result. But of course there's framework delay, network delay etc. Many of which are infrastructure-dependent, thus difficult to avoid/optimize.) Option B. is to create a new connection for each AJAX request, and close it when the AJAX request has finished. This would reduce the TCP connection/session setup overhead in that only one would be required per event round-trip. However, our application uses the ZK framework, which is event-based. As a consequence, the framework doesn't provide us with hook points where we'd learn when the handling of an AJAX request starts and when it ends. Instead, execution is event-driven and may involve exceptional control flow. In short, we couldn't reliably close those connections. Option C. is the use of connection pools. When an AJAX request arrives, we execute our application logic. Whenever we reach a BaseX query/update/command in the execution, we check for an available connection. Up to a maximum number, we create new connections on demand. If the maximum number is reached, we wait (we could also reject the request, there are different load management options here). We use that connection, independent of which queries/updates/commands were previously executed within the session that this connection represents. That's why it's important for us that BaseX provide means to avoid inadvertent session state. For these reasons, we believe that the use of connection pools is an appropriate means to handle connection management to the BaseX server. What experience do others have that use BaseX as a database tier in their web applications? - Godmar [1] https://github.com/BaseXdb/basex/issues/551

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Re: [basex-talk] soya lecithin,feed additive
by tjboshuai_bella 10 Aug '12

10 Aug '12

Dear Sirs, Glad to know your company,We are a specialized Chinese manufacturer of soybean lecithin more than 10 years. Our website: www.tjboshuai.com for your reference. Application: 1.used in the food as food additive,worked as emulsifier release agent and so on,widely used in the chocolate,ice cone,milk,biscuits,confectionary ; 2.used in the animal feed as feed additive,to prove the animal feed's quality and enhance the nutrition of the feeds; we have different grade ,type product ,which one do you want to use?food grade or feed grade?some information for your reference. We highly appreciate your email and sincerely hope we can get further cooperation.have a good week Bella Company name:Tianjin Boshuai Industrial & Trading Co.,Ltd Website:www.tjboshuai.com Phone:022-27915570 022-27396299 Fax:022-27920127 Email: tjboshuai_bella(a)yahoo.com.cn MSN: tjboshuai_bella(a)hotmail.com tjboshuai_bella

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Re: [basex-talk] feed additive,soya lecithin
by tjboshuai_bella 10 Aug '12

10 Aug '12

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XQuery update: multiple document nodes with the same path
by Francis Avila 10 Aug '12

10 Aug '12

I'm having trouble understanding document/collection semantics with xquery update. If a create a document and add another document to the same path, that path becomes a collection with two document nodes. However it seems to be impossible to manipulate these document nodes individually. See the following console output: > create db test Database 'test' created in 137.25 ms. > open test Database 'test' was opened in 2.15 ms. > add to test.xml <root1/> Path "test.xml" added in 19.44 ms. > add to test.xml <root2/> Path "test.xml" added in 2.57 ms. > list test Input Path Type Content-Type Size --------------------------------------- test.xml xml application/xml 2 test.xml xml application/xml 2 2 Resources. > xquery collection('test/test.xml') <root1/><root2/> Query executed in 30.84 ms. > xquery doc('test/test.xml') Stopped at line 1, column 20: [BXDB0006] Database path 'test/test.xml' must point to a single document. > xquery import module namespace functx = "http://www.functx.com"; collection('test/test.xml') ! (document-uri(.), functx:node-kind(.), .) test/test.xml document-node<root1/> test/test.xml document-node<root2/> Query executed in 29.54 ms. > xquery delete node collection('test/test.xml')[2] Query executed in 1.18 ms. > xquery import module namespace functx = "http://www.functx.com"; collection('test/test.xml') ! (document-uri(.), functx:node-kind(.), .) test/test.xml document-node<root1/> test/test.xml document-node<root2/> Query executed in 43.83 ms. > xquery delete node db:open('test','test.xml')[2] Query executed in 2.15 ms. > xquery import module namespace functx = "http://www.functx.com"; collection('test/test.xml') ! (document-uri(.), functx:node-kind(.), .) test/test.xml document-node<root1/> test/test.xml document-node<root2/> Query executed in 36.77 ms. Note that it doesn't seem possible to delete one of the document nodes, even using db:replace() > xquery db:replace('test','test.xml',collection('test/test.xml')[1]) Stopped at line 1, column 60: [BXDB0006] Database path '%' must point to a single document. I don't understand this error message, unless db:replace is internally using the path of the document-node rather than the document-node itself. > delete test.xml 2 resource(s) deleted in 36.35 ms. But I can delete both items at the same path. The way I discovered this is that I accidentally added a document to an existing path using db:add(). However, I was unable to correct the mistake and remove the documents without completely deleting the path and re-adding its members. I don't see any way to do this with a single xquery update PUL. It seems to me that this is a bug. Either xquery update expressions like 'delete node' should work on document nodes, or adding document-nodes to a path which has a document-node should be illegal and raise an error when attempted. -- Francis Avila

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freies Geschenk
by hi 09 Aug '12

09 Aug '12

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Hadoop with QueryProcessor
by Tiago Freitas 07 Aug '12

07 Aug '12

Hi. I'm trying to use the BaseX QueryProcessor with Hadoop to process very large XML files. I use an XmlInputFormat to split the XML files, and process each node with BaseX. I prefer to use QueryProcessor for this and not the server (each individual element is not very large and I don't want to store the input files on a BaseX server). The problem is when I use modules in the query, BaseX can't open the module files in the distributed filesystem. I get "[XQST0059] Could not retrieve module …". I'm passing the query using "new QueryProcessor(query_string, basex_context);", and the bind method for the input. Is there a way to include the module programmatically so the QueryProcessor doesn't try to open the xquery file? Maybe with org.basex.query.util.pkg.ModuleLoader or QueryContext.module but I din't figure how to do it yet. Regards

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Clustering/replicating/high availability
by Philipp Kamps 04 Aug '12

04 Aug '12

Hi, I'd like to pick up that topic about clustering and high availability. I found a message from October 2011, you mentioned that there are a couple students working on that topic. Any updates? Maybe they could describe the approaches? That would be awesome. Have a good weekend. Philipp

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Hallo
by hi 04 Aug '12

04 Aug '12

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Redo log
by Henrique Oliveira 03 Aug '12

03 Aug '12

Hi there, Does Basex use redo log to reduce the risk of a system failure occurring while updating the metadata store? regards -- Henrique Oliveira

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What is the easiest approach to edit data in a browser and have that data stored as xml in basex
by Alex Muir 01 Aug '12

01 Aug '12

Hi, So I've got a client interested to create a dataset of music information such as artist, track name, album release year... and store that in XML. Non technical users would need to view and edit the music info in a web interface and the data would be stored in XML. I was looking at Typo3 which seems to be able to work with basex. I wonder what is the easiest approach to edit data in a browser and have that data stored as xml in basex? What are CMS solutions that work with basex? Is typo3 a good solution? Regards -- - Alex G. Muir Software Engineering Consultant Linkedin Profile : http://ca.linkedin.com/pub/alex-muir/36/ab7/125

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BaseX-Talk August 2012