Q: oracle data files & performance

Hi ,
I've received a two interesting questions from a collage of mine.  

1)
If two processes are writing to the same file , will they suffer from some conation on the file handler ?
Do you think that spreading very busy tables (has a lot of inserts from different sessions) on different tablespaces (which will be translate to different data files ) will have better I/O performance over one single data file ?  

I'm talking only from performance perspective , not from backup & recovery ?  

2)
If we have tablespaces with several data files . Will oracle allocate extents in a round-robin fashion between the files or will he fill one data file and then pass to the another data file ?      

Amihay Gonen
DBA,

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