I'm running 9i 9.2.0.1 64-bit on Solaris 9. My current parameter is db_block_size=4096.

My questions:
1. Can I change the parameter to 8192 in the spfile and restart the DB so that the new value is in effect?
2. Do my existing datafiles which are created using 4096 bytes block size able to extend to 8192 bytes?
3. For my environment what is the recommended block size for best performance?

Thanks.