One of the reasons we use relational database technology is that existing RDBMS implementations provide extremely mature, scalable and robust concurrency control. This means much more than simple read/write locks. For example, databases that use locking are built to scale efficiently when a particular transaction obtains /many/ locks - this is called /lock escalation/. On the other hand, some databases (for example, Oracle and PostgreSQL) don't use locks at all - instead, they use the multiversion concurrency model. This sophisticated approach to concurrency is designed to achieve higher scalability than is possible using traditional locking models. Databases even let you specify the required level of transaction isolation, allowing you to trade isolation for scalability.
There were quite a few comments in response to my post about Criteria queries. I finally get around to responding. A number of people suggest a more tree-oriented approach, where we treat all logical operators as binary. For example, anonymous suggests the following:
About two years ago, a co-worker asked me innocently:
What are scalar types anyway?
Chris Winters doesn't like object-oriented query APIs. Since Hibernate emphasizes the query /language/ approach, I'm not the best person to disagree with him here. Criteria queries are usually noisier, no doubt about that. And the query languages I've seen tend to be more expressive. Writing arithmetic and even logical expressions is a breeze in a query lanugage, but certainly not in an object-oriented Criteria API.
Names are important in computing. Really Important. I'm not talking about calling classes sensible things like UpdateUserDetailsCommand in preference to UpdUDetsCd. I mean the names of products themselves. A great name tells us lots about a piece of software: it tells us that the creater has some imagination, a sense of style even. It tells us that this person is serious about the success of the product, that they understand that there is more to making great software than writing great code.
One of the great improvements in Hibernate 2.1 is that we finally have a mature Criteria query API. For a very long time I let this feature languish because I just wasn't sure what it should really look like. Every QBC API I've looked at is designed differently and there is certainly nothing like a standard API to learn from. I've seen everything from this:
We are taking a close look at SDO. It's an interesting spec that comes a bit out of left field. My reading is that it provides a mechanism for manipulating and especially for externalizing graphs of objects or things that look sufficiently close to objects to be meaningfully represented as a
graph. For example, XML.