RE: informix vs oracle

Man, are you just trawling or what :-? > -----Original Message----- > From: owner-informix-list@iiug.org > [mailto:owner-informix-list@iiug.org] On Behalf Of utkanbir > Sent: 17 March 2005 15:34 > To: informix-list@iiug.org > Subject: informix vs oracle > > Hi Gurus , > > After 7 years with informix and 2 years with oracle , these are my own > comments about them. All the comments / corrections are wellcomed: > > 1. backup / restore > > informix : the backup set is a complete object . It does not depend > anything .It can be used as the only object in order to do restore. > > oracle : lots of things must be considered. You must know what you > do. 'I just want to backup and restore my db ' is not enough. To do a > complete restore of the db , first it is necessary to copy all the > files to a backup location (including datafiles,control files, undo > and redo log?no be careful if you want to recover the db after copying > files back , you need current logs so backing up redo logs are not > necessary . On the other hand copying entire datafiles before any type > of incomplete recovery is very important . (in order to restore a db , > copying the files once again huh...) And dont expect the ontape -r > command's lovely message: do you want to backup the current logs? No > such a thing exist....) > > If someone who only knows oracle ,doesnt know aynthing about the other > databases , this backup method can be the best one. But if you know > the other databases restore backup methods, oracle method is much more > difficult and complex. > > > 2. Parallel query > > oracle : parallel query bypasses the buffer cache. it directly reads > data from the disk into the user process's pga memory . It also does > not check whether a block is cached in memory or not , it reads the > disk every time. So same parallel query executed several times makes > the same amount of disk io . > > > On the other hand , parallel query architecture is more flexible than > informix. It does not depend on tablespace number / partition . And > parallel dml , parallel optimizer hints are very rich. (last veison of > informix i used is 9.2 so may be informix have some improvments which > i dont know) > > > > 3. Nologging operations: > > > In oracle , it is possible to do certain operations without generating > redo log . These are called unrevorable operations : > > create table test nologging as (select * from dual)> > insert /*+append */ into a select * from dual > > these operations is not logged in redo logs so cant be reovered. > > But the drawback of such an operation is , if you have to recover the > db server or datafile by using redo logs , the entire table becomes > useless. Not > only these insert statements are invalid but also the whole table. > > 4. multi-versioning > > oracle has no dirty read concept but instead multi-versioning . So if > session a updates data , session b see the previous version of the > recods .But this can also happen for a long running queries!Although > no updates take place , lots of different versions can be put in > memory especially if your db is a datawarehouse type. > > > Kind Regards, > hope > Disclaimer http://www.shoprite.co.za/disclaimer.html sending to informix-list