Wichert Akkerman wrote: > On 11/13/09 21:33 , Shane Hathaway wrote: >> I've been studying how to build an enormous database based on what I >> know. There are an incredible number of distributed databases these >> days, but all of them concern me in one way or another. > > Can you share some of those concerns with us? I'ld be interested to hear > what kind of problems you see.
The best article I've found is a simple presentation and overview: http://highscalability.com/blog/2009/11/5/a-yes-for-a-nosql-taxonomy.html The article neatly categorizes a lot of the NoSQL databases. It suggests that document stores have the right level of complexity. Wide columnar stores like Cassandra could be too complicated to gain a lot of traction, while simpler databases might lack features we would normally take for granted. In other articles, I learned about CouchDB conflict resolution. CouchDB allows any conflict and it stores both conflicting values, expecting the application to resolve the conflict later. Clearly, CouchDB is designed to solve the PDA use case: I change a contact's phone number differently on my PDA and my desktop, then when I sync, I click some UI button to indicate which is correct. I think that sort of conflict resolution would cause security holes for the application I am working on, but it would probably work for a lot of other applications. Current versions of CouchDB expect applications to scale using replication. Replication is not a substitute for sharding. The couchdb-lounge project seems to be solving that with proxies: http://tilgovi.github.com/couchdb-lounge/ The Mongo DB guys have a pretty thorough and fair comparison of CouchDB and Mongo: http://www.mongodb.org/display/DOCS/Comparing+Mongo+DB+and+Couch+DB The bottom of the page lists use cases for MongoDB. It says people building a system with "very critical" transactions should choose a traditional RDBMS. That seems like reasonable advice for the application I'm building, except that I consider ZODB to be at least as reliable as an RDBMS. (RelStorage uses a subset of RDBMS functionality that I have found to be reliable.) I think that by "very critical", the MongoDB authors are referring to applications that must not allow conflicting updates. Conflict resolution is probably my main concern with all of these new databases. I have no doubts about ZODB's conflict resolution policy, while I can imagine a variety of different policies these other databases might implement. A "four or five dimensional hash" like Cassandra might even have a conflict resolution policy that changes with every release. Shane _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev
