Re: Isolation levels in Informix vs Oracle

DA Morgan said: > rkusenet wrote: > >> "PK" <pk26au@yahoo.com> wrote in message >> news:667bf0c6.0412150133.7e4ce123@posting.google.com... >> >>>Hi, >>> >>>As you know Informix offers 'set isolation to dirty read' - a facility >>>to read dirty buffers. I believe DB2 UDB too offers it but not Oracle. >>> >>>What is the neccessity or justification for an RDBMS to offer such a >>>feature and do applications really need it ? I was told by an Oracle >>>guy that Informix and DB2 are 'forced' to offer this because of their >>>architecture and this is not a 'feature' as such ! He says Oracle can >>>offer it in a 'jiffy' by pointing to its undo tablespace (where before >>>images of a buffer are kept before modifications) but they will not as >>>this is not justified ! >>>I myself (worked with Informix for 9 yrs but now into Oracle for past >>>1 yr ) feel its quite cool. However I would like to get expert >>>technical opinion. I don't intend to start a flame at all ! >> >> >> dirty read is very useful when the application gurantees that the data >> being >> read is at that instant read-only. For e.g. in a transaction table where >> you >> are generating report for yesterday. You know for sure that all new >> records >> in that table will be for today only. Why bother locking. Dirty read >> will >> do the job just as fine with minimum resource contention. > > The problem with your analogy is that if by definition it is yesterday's > (or read-only) data and no changes are taking place you don't have > anything dirty to read. With read-only data any database, with any > transaction type, will give a valid answer. > > Can you address the dirty read issue in a situation where there truly is > dirty data. Yeah, I'll have a go: quite often in the sites I work in, they want a snapshot report on the status of the business (how many orders have we taken today, what's our month-to-date position on metric X, etc.) By the time the report has finished printing or comes up on screen, it's out of date, but the manager wants a rough idea of where s/he is. In this case, the "committedness" of the data isn't material. -- Bye now, Obnoxio "C'est pas parce qu'on n'a rien ' dire qu'il faut fermer sa gueule" - Coluche "I'm trying to see things your way, but I can't get my head up my ass" - JCH "Ogni uomo mi guarda come se fossi una testa di cazzo" - Marco I went to the airport to check in and they asked what I did because I looked like a terrorist. I said I was a comedian. They said, "Say something funny then." I told them I had just graduated from flying school. -- Ahmed Ahmed sending to informix-list