- From: <noah_mendelsohn@us.ibm.com>
- Date: Tue, 15 May 2007 15:09:44 -0400
- To: "Michael Kay" <mike@saxonica.com>
- Cc: "'Jones, Kevin'" <kevin.jones@intel.com>, xmlschema-dev@w3.org, "'Le, Yongnian'" <yongnian.le@intel.com>, "'Yu, Zhiqiang'" <zhiqiang.yu@intel.com>
Michael Kay writes: > As far as I can see you are conjecturing performance > difficulties here with no real evidence. I don't think there is > any reason to believe that the cost of validating identity > constraints is likely to be a significant obstacle to real applications. My intuition matches Michael's, with a couple of minor caveats: 1) Just because one can build efficient id-constraint implementations doesn't mean that any particular one you try to benchmark is built to be efficient. Finding a slow implementation doesn't settle the question of whether the feature is inherently hard to optimize. Finding a fast implementation at least shows what's possible. 2) I think it's clear that there are pathological uses of identity constraints that are likely to be slow. For example, you could arrange in some schema and instance so that the keys would contain a significant fraction of the information in a document (a document that has mainly attributes, all of which are used in keys); if the document were gigabytes long, then you could get gigabytes of key data. I expect that many implementations will at least sometimes build key tables, and in a distorted example like this, those could get large and slow. My intuition matches what I take to be Michael's position: if you use id constraints in the obvious and intended ways, then the implementation overhead should be modest or negligible, for some definition of modest and negligible :-) Noah -------------------------------------- Noah Mendelsohn IBM Corporation One Rogers Street Cambridge, MA 02142 1-617-693-4036 --------------------------------------
Received on Tuesday, 15 May 2007 19:09:35 UTC