On 3/22/07, Michael Stone <mstone+postgres@xxxxxxxxx> wrote:
On Thu, Mar 22, 2007 at 06:27:32PM +0100, Tino Wildenhain wrote: >Craig A. James schrieb: >>You guys can correct me if I'm wrong, but the key feature that's missing >>from Postgres's flexible indexing is the ability to maintain state >>across queries. Something like this: >> >> select a, b, my_index_state() from foo where ... >> offset 100 limit 10 using my_index(prev_my_index_state); >> > >Yes, you are wrong :-) The technique is called "CURSOR" >if you maintain persistent connection per session >(e.g. stand allone application or clever pooling webapplication) Did you read the email before correcting it? From the part you trimmed out: >The problem is that relational databases were invented before the web >and its stateless applications. In the "good old days", you could >connect to a database and work for hours, and in that environment >cursors and such work well -- the RDBMS maintains the internal state of >the indexing system. But in a web environment, state information is >very difficult to maintain. There are all sorts of systems that try >(Enterprise Java Beans, for example), but they're very complex. It sounds like they wrote their own middleware to handle the problem, which is basically what you suggested (a "clever pooling web application") after saying "wrong".
Tino was saying that rather that build a complete indexing storage management solution that lives outside the database, it is better to do intelligent session management so that you get the simplicity if a two tier client server system but the scalability of a web app. Web apps are not necessarily stateless, you just have to be a little clever about how database connections are opened and closed. Then you get all the database stuff that comes along with a persistent connection (advisory locks, cursors, prepared statements, etc) without building all kinds of data management into the middleware. merlin
