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