April 2001 - Zope-Dev

Postgres DAs and Serializable Isolation Level
by Randall F. Kern 07 Apr '01

07 Apr '01

This post is about fixing the "ProgrammingError: Can't serialize access due to concurrent update" exceptions you will often get when using PostgreSQL with Zope. First a little background on the error, for those of you not familiar with Postgres's transaction isolation. ANSI defines 4 levels of transaction isolation for SQL: Read uncommitted, Read committed, Repeatable read, and Serializable. Postgres implements both Read committed, and Serializable. Read Committed is what most people expect from a database; SELECTs give the most up to date information, but don't show results from other transactions that have not been committed (this means two identical SELECTs run back to back in the same transaction may produce different results). Serializable transactions only see data committed before the transaction began (in this case, the identical SELECTs will always return the same data). Concurrent updates are not supported in the serializable transaction mode; if one transaction tries to update (or delete) a row that has already been updated by a concurrent uncommitted transaction, the second transaction will fail with a "concurrent update" error. In most cases, the proper response to an error of this type is to simply redo the entire transaction. It seems that ZPoPyDA and ZPsycopgDA both default to running in the Serializable isolation level, rather than the Read Committed isolation level. This is of course kind of slow, and with most queries isn't required. However, it will produce the most robust results. Given that the default transaction mode for these DAs is Serializable, and Zope has this nifty support for ConflictErrors and retrying transactions already, I propose Postgres DAs should convert the concurrent update serialization errors into ConflictErrors automatically. I've been running this way for a few days, and everything seems great. Any reasons why this might be good/bad/ugly very welcome. (Like: is it safe to throw a ConflictError at any random time during processing? >From a quick glance at ZODB it seems they are only thrown at commit time now) Here is a small patch to ZPsyccopgDA 0.5.1 that implements this change: ZPsycopgaDA/db.py 100a101,102 > from ZODB.POSException import ConflictError > 183c185,191 < r = c.execute(qs) --- > try: > r = c.execute(qs) > except psycopg.ProgrammingError, perr: > _serialize_failure = "ERROR: Can't serialize access due to concurrent update" > if perr.args[0][:len(_serialize_failure)] == _serialize_failure: > raise ConflictError > raise -Randy

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Help regarding databse & variable management
by Honey George 07 Apr '01

07 Apr '01

Hello, I have a problem in database connectivity in Zope with Postgres. If anybody can help me in this regard please reply asap. I want to insert a row into a tabel, get a unique id from the table and make another entry into another table.I am able to insert into the forst table and retrieve the unique ID. But while trying to insert into the next table, it says no value for the unique id retireved. Expecting a solution. Reagrds, George __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/

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DBObjects 1.0 and Demos for Proiektor & ZQuest released
by Stephan Richter 07 Apr '01

07 Apr '01

Hello everyone, iuveno AG, Ingolstadt Germany, has made available a demo and products page, releasing several products: THE LINK: http://demo.iuveno-net.de/ 1. DBObjects 1.0 - DBObjects is a framework that maps relational data to a Zope object tree. It provides many features (such as SQL Method auto-generation) and saves up to 95% development time on object creation with relational data. API Documentation, a Demo, Feature List and so on are available on the site. 2. Proiektor - Proiektor is a groupware and project management system developed by iuveno. It is based on DBObjects and implements a nice set of features with some unique design ideas. But see yourself... 3. ZQuest - ZQuest was originally written for a university as testing tool and is now also developed by iuveno AG. It has a good set of features, especially for scientific questions. ZQuest uses DBObjects of course. If you are interested, click on the link above ... 4. CMS - Our Content Management System is coming soon with a true user-friendly management interface... ALL THESE PRODUCTS ARE OPEN SOURCE!!! Please feel free to contact me any time via E-mail (srichter(a)cbu.edu or stephan(a)iuveno.de) or via phone at +1-901-230-ZOPE (9673). I hope you enjoy! Regards, Stephan -- Stephan Richter CBU - Physics and Chemistry Student Web2k - Web Design/Development & Technical Project Management

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iuveno Products Page - DBObjects, Proiektor and ZQuest - FIXED
by Stephan Richter 07 Apr '01

07 Apr '01

Okay, I think the old version of our CMS system did not like the new Zope too much. I have taken this demo out of the site (since it was not available in anyway) and ran 'wget' extensively (I started 100 threads running a recursive wget). If you still experience difficulties, please let me know. The Link again: http://demo.iuveno-net.de/ Regards, Stephan -- Stephan Richter CBU - Physics and Chemistry Student Web2k - Web Design/Development & Technical Project Management

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ZUnit 0.2 is coming!!!
by Lalo Martins 07 Apr '01

07 Apr '01

Hi there extreme people :-) We're about to release ZUnit 0.2, after an almost total rewrite. Only thing we're missing is a "Run tests" tab in the TestRunner object, and then remove a lot of reminders and debugging instructions. If you're feeling bold (it works, after all), there is a preview release at http://www.zope.org/Members/lalo/ZUnit/ZUnit-0.2pre1.tar.gz - but this is a File object, not a Product Release, and I won't link to it anywhere! It's just for developers' eyes :-) []s, |alo +---- -- I say a prayer now our love's departed That you'll come back to stay Bring back the perfect day http://www.laranja.org/ mailto:lalo@laranja.org pgp key: http://www.laranja.org/pessoal/pgp Brazil of Darkness (RPG) --- http://www.BroDar.org/

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setattr and skinscript
by kent＠tiamat.goathill.org 06 Apr '01

06 Apr '01

I have a Specialist which I am using to programmatically load table data into a rack with. When I add a skinscript to query the rack, my setattr, which is used to set the row attributes produces the following error: 2001-04-06T22:45:03 PROBLEM(100) ZPatterns Error computing attribute SID Traceback (innermost last): File /var/zope/Products/ZPatterns/AttributeProviders.py, line 315, in _AttributeFor (Object: GAPMixin) File /var/zope/Products/ZPatterns/Expressions.py, line 122, in eval File --/DocumentTemplate/DT_Util.py, line 334, in eval (Object: SQL_getTable ( entry_id = self . id )) (Info: self) File <string>, line 0, in ? File --/DocumentTemplate/DT_Util.py, line 138, in careful_getattr File /var/zope/Products/ZPatterns/Expressions.py, line 53, in validate File --/AccessControl/SecurityManager.py, line 144, in validate File --/AccessControl/ZopeSecurityPolicy.py, line 168, in validate Unauthorized: id my skinscript currently only has the SQL_getTable() method referenced and it appears that the rack is atempting to obtain the current value for the attributes I am attempting to set in the rack item, and I have only just created the item so none are there. 1) Is there a way to override the skinscript attempting to access the item's attributes when I am attempting to set them? barring that, 2) How do I otherwise deal with the skinscript attempting to access the attributes? If I don't provide the skinscript, I can set the item's attributes just fine directly in the rack. Is there another way that I am supposed to be setting row (item) attributes than using setattr() for a ZPatterns rack? Thanks

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Re: [Zope-dev] Memory problems with ParsedXML ?
by Karl Anderson 06 Apr '01

06 Apr '01

Godefroid Chapelle <gotcha(a)swing.be> writes: > Karl Anderson a écrit : > > Another thing to keep in mind is that the ParsedXML *product* is a DOM > > tree and a management interface around it. The management interface > > only gives you a convenient UI and a place to store a few bits that > > the DOM doesn't know about (content type, namespace usage, etc.). > > It's always more efficient to just use the DOM tree and related > > utilities (parsing, printing), although it is less convenient - you > > have to know a little bit more about what you're doing. Do you need > > each of those 2500 product instances? See the createDOMDocument > > method to create a DOM document without the management interface. > > > > I am trying to use createDOMDocument, calling it from an external method: > > from Products.ParsedXML import ParsedXML > > def accessXml(document): > return ParsedXML.createDOMDocument(document) > > When using the document returned in a python script, it seems that Zope > security prevents me from accessing any DOM attributes. > > Am I doing something wrong or am I forced to do everything through external > methods ? The DOM objects without the ParsedXML management proxies don't have any Zope security information associated with them, so you have to provide it yourself. This is one of the things that the management proxies provide. I didn't mean to sell the proxies short; I should have mentioned that you have to know about providing the features youself that they provide, including security, so this is an area for Zope experts. I've added this to the README. Furthermore, if you're just calling methods on the Document node, without traversing to its subnodes, you're really not paying much of a price; you're basically just putting more function calls between you and the DOM object until you access a DOM subobject. I don't use the python scripts much, but they have very restricted security, being web-edited and all. So yes, one way to give access is to use external methods. Another way is to use a python product and the security machinery available to you there. The unproxied DOM objects are similar to any non-Zope aware python class instances with regards to security; if you're unfamiliar with it, I'd play around with some non-Zope aware dummy class instances, with nested subinstances and attributes, until you know how to make those objects and attributes publishable. -- Karl Anderson karl(a)digicool.com

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Zope developers wanted
by Jörg Dennis Krüger 06 Apr '01

06 Apr '01

Hi all, I'm actually scheduling a web-project, which should be done with Zope. For this project I'm seeking for Zope developers. If you a familar to developing applications based of the Zope application server and have time for working on a project, please contect me! Yours, Dennis -- Jörg Dennis Krüger Sintpertstrasse 13 81539 München Telephone + Telefax: +49-(0)700-JDKRUEGER (53578343) http://www.jdk.de mailto:jdk@jdk.de "Zwei Dinge sind unendlich: Die menschliche Dummheit und das Universum. beim Universum bin ich mir noch nicht ganz sicher...", Albert Einstein

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Help On Database Connectivity
by Honey George 06 Apr '01

06 Apr '01

Hello, I have a problem in accessing postgres database from zope. I am able to access the database from the Z Sql method directly. Can anybody help me in accessing the database from a DTML documents. There parameters will be passed from an HTML form. Regards, George __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/

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Bug in ZMI?
by E. Seifert 06 Apr '01

06 Apr '01

Hi list, I think I encountered a problem with the ZMI. Everytime I added a new property to the memory cache object the list doesn't display them correctly. They are concatenated; no space between them. Is this a known bug? Bye Eric

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