[Zope-dev] Declaring Dependencies for XML documents (Was: How To Improve CacheCoherency for RAM/Disk Cache Manager...?)
Jamie Heilman wrote: Why make the unlucky user pay the price? Because the unlucky user (which I read as: author) is the only one who knows the required behavior of their code. Allow me to clarify -- I meant the end user browsing the website. I hate it when I surf to a less-highly-used portion of a website and have to wait 30 seconds for the page to render. Anyway, after talking this over with my colleague, I realize that the problem of *deriving* dependencies is fundamentally undecidable. We might be able to figure it out in the case of simple acquisition, like But it is hopeless for pure python: :) One possibility is to add the ability to *declare* dependencies. I thought of doing that for an X-path aware "XML Composite Document" object. It is an object that produces a valid XML document by grabbing parts of other Zope objects via XPath/XPointer/XInclude. Such an object could have an explicit listing of the objects on which it depends, and invalidate the cache appropriately whenever any of the dependent objects changed. http://www.zope.org/Members/faassen/SimpleCache Is a nice beginning along these lines. Thoughts? --Craeg ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] How To Improve Cache Coherency for RAM/Disk Cache Manager...?
> Why make the unlucky user pay the price? Because the unlucky user (which I read as: author) is the only one who knows the required behavior of their code. ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
[Zope-dev] How To Improve Cache Coherency for RAM/Disk Cache Manager...?
Hello: I am getting ready to release the next version of XMLTransform, and in revisiting the Caching strategy for the product, I realized there are larger issues that probably deserve a discussion here. The bottom line is that transforming XML to something else via XSLT is a potentially expensive operation, so that caching the results is often worthwhile. As I thought about the problem, I realized that this probably holds true for any sufficiently dynamic site where you employ caching because: - the cost of processing exceeds the cost of retrieval from cache by at least an order of magnitude - there are many more readers than writers Question: How can we ensure cache coherency? For example, you might have a ZPT that includes the results of several long-running PythonScripts, whose rendered result is cached. What happens when the code for those PythonScripts changes? Worse, what happens when the SQL data retrieved by the Z SQL Method that the PythonScripts operate on changes? Correct me if I am wrong, but today the Zope Cache Management facility takes into account changes in cached objects, but not objects on which they depend. One strategy for accounting for this problem is to invalidate objects in the cache based on a certain interval. That way objects are out of date for at most the length of the interval. This could be called the "pull" or reactive model. Alternatively, Cacheable objects might be somehow aware of the objects on which they depend, and invalidate themselves in the cache when one of their dependent objects changes. This could be called the "push" or proactive model. Depending on some parameters, they might even recalculate their results proactively so they could be re-cached immediately. Why make the unlucky user pay the price? The latter alternative is not infeasible. DTML and ZPT scripts must parse their contents in order to render, so the information is available somewhere. The question is: can/should this be addressed for Zope2? What about Zope3? Is one model more appropriate for a development setting (equal numbers of writers and readers) vs production (many more readers, few or no writers)? Any thoughts or sage advice on this topic would be much appreciated! Regards, --Craeg ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Prevayler and "Object Prevalence"
On Monday 03 March 2003 3:48 pm, John Ziniti wrote: > Any ZODB developers read this article at /. and the accompanying > one at developerWorks? Would anyone care to comment about > the relevance/comparisons of "prevalence" to the concepts of > persistence used in ZODB and/or ZEO? I had looked at this (and the python port) briefly last year The main advantage of ZODB over a relational approach is that it can *automaticly* add ACID conditions to application logic objects, without major code changes. It is possible to think about your application logic and ignore the ODB aspects. Until recently, using a relational store for objects meant adding intrusive persistence code and breaking encapsulation. As I understand it, prevayler preserves encapsulation, but still requires the intrusive code changes. It relies on separating appliction logic from the object store. Application logic can only read and write to the object store using remote method calls, which prevayler calls persistent "command objects". Commands are processed by a single threaded server process. Command objects have to be persisitent because durability is provided by writing them to a log file, and replaying commands on recovery. There is no way to apply transactional semantics to application logic, except by cramming all the work into one big command object. (I hope that helps. Appologies in advance for any inaccuracies) -- Toby Dickenson http://www.geminidataloggers.com/people/tdickenson ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
[Zope-dev] Prevayler and "Object Prevalence"
Any ZODB developers read this article at /. and the accompanying one at developerWorks? Would anyone care to comment about the relevance/comparisons of "prevalence" to the concepts of persistence used in ZODB and/or ZEO? http://developers.slashdot.org/article.pl?sid=03/03/03/1220222&mode=nested&tid=156&threshold=1 Just looking for some info. Thanks in advance, JZ ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
[Zope-dev] HTTP Response headers in ZPublisher.HTTPResponse
Yo,
the response headers set in ZPublisher.HTTPResponse our not always RFC
compliant. In case of exceptions you get: (round lines 670 in
HTTPResponse.py)
if ev.find( '') >= 0:
ev = 'bobo exception'
self.setHeader('bobo-exception-value', ev[:255])
If the content is a xml,wml,whtml,... page, this results in exception
headers like:
Bobo-Exception-Value:
while most browsers will not barf on this, we encountered numerous
problems with wap-gateways refusing to swallow this.
Another question is whether it is wise to send things like
the file and line numbers where the exception took place to the client.
I can understand that it can be useful in debug mode, but I can't see a
reason to do this in a production setup.
The simplest way of fixing this is to change the code to something like:
ev = 'bobo exception'
self.setHeader('bobo-exception-value', ev)
or to leave out these headers altogether.
Romain.
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[Zope-dev] Re: [ZODB-Dev] standalone ZODB for large Numeric arrays
AFAICT, AdaptableStorage is designed to allow this kind of thing. Shane? Sounds interesting. I am going to search for this. Yes, it is. I don't know anything about NetCDF, but it sounds intriguing. I guess NetCDF is not just an encoding format, but also some kind of database for large arrays. Shane http://my.unidata.ucar.edu/content/software/netcdf/index.html NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. Python interface is contained in Konrad Hinsens Scientifc package http://starship.python.net/~hinsen/ScientificPython/ Mike ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
