Re: Stateless clients and locking schemes (or rather isolation levels)

Serge Rielau wrote: > Superboer wrote: > >>> This is a funny way of looking at. Obviously Oracle's none locking >>> engine is perfectly suited to scaling multi user applications, >>> particularly when most people are developing for stateless clients. >> >> >> >> ahum does the above explain why informix was faster on a 5 times >> smaller machine then obstacle...???? >> >> Superboer. >> > Changed the subject lines and following up on what Knut started. > > How does Oracles snapshot isolation help with stateless clients. > To the best of my knowledge snapshot semantics only operate on either a > statement or a transaction level. In a stateless scenario I'd assume > that teh application transaction covers at least two database > transactions. A read phase wher the resultset is displayed at the client > and a separate write phase where the modified data is written back. > How does snapshot isolation help here? > Informix supports versioning columns which can be used by the app to > prevent overwriting other users changes across DB transaction boundaries. > MS SQL server has a somewhat similar approach and even buried optimistic > locking into the cursor logic (not applicable in a stateless enviroment > (no cursor open). > I see tha value of snapshot isolation for certain purposes. I don't see > it for a 3 tier web application.... well. may be not. i went back to Weikum/Vossen, chapter 5. sounds like an approach. and a google for +multiversion +concurrency +"3 tier" came up with this. kind of funny, really. http://sapdb.2scale.net/moin.cgi/FeatureEnhanceProposals BTDBB > > Thoughts? > Cheers > Serge