[Lazarus] Web development and XML database (Mattias)
juha.manninen62 at gmail.com
Thu Nov 17 10:38:25 CET 2011
2011/11/17 Mattias Gaertner <nc-gaertnma at netcologne.de>
> It's a lightweight database for XML files. That means you give it a list
> of directories and it will load/parse all xml files including
> subdirectories into memory for fast access.
> You can query via simple HTTP requests and get xml. So you are not
> limited to FPC, you can use any language.
> There are several types of query, including some with XPath
> expressions. At the moment it supports only a few XPath features, but
> they are already quite powerful.
> When a file was edited/changed you can trigger a rescan or you can
> rescan in interval. A rescan on a thousand directories to search for
> modified files usually takes 10-100ms and is done in separate threads to
> not disturb the queries. It parses about 5-20MB per second per core and
> automatically uses all cores.
> It is currently used by two projects, that were migrated from eXist DB.
> One is running on an OS X server, the other on a Linux server. They
> have thousands of directories, more than 150MB of XML files, which
> refer to others in various ways.
Thanks for the explanation.
In essence it is a database optimized for reading but not writing.
For updating the XML file contents there is no concurrency checks or atomic
That is fine with many use cases but for example e-commerce sites could not
use it. They need safe transactions for user profile and sales action
This is partly why the SQL databases are slow, they take care
of concurrency also when data is updated.
Your solution could be used to provide fast access to a slow SQL DB data by
generating data dumps eg. once a day.
eXist DB is made with Java. It would be interesting to compare how much
their performance differs. Java has become very fast but it still hogs
Good luck with the project!
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