Working on getting an import to scream along. Just curious why Oracle docs suggest to set commit=y to improve the performance of a large import? I mean I can do test case after test case to show why one would not frequently commit in btach processing, what makes import so special?
I don't know why commit=y should improve performance either, but I believe that there is an exception to this rule. When importing LONG,LOB,BFILE,REF,ROWID or type columns array inserts aren't done, so a commit is performed after each row. They say that for tables with these kind of columns it is preferable to set commit=n (and hope your rollback segments are big enough!). I'm going to be working on similar project to yours this week, and i'm going to benchmark LONG column imports with commit=y and commit=n. I'll let you know what I find out.
Also, you might find this free tool of interest (I've not used it myself):
If you do not use commit=y then Oracle (by default) will try to import the ENTIRE table before issuing a commit. This can be a vewy ( Elmer Fudd influence) bad thing if you have large tables, it can kill your RBS or redo, or undo, or whatever the hell you want to call it.
I usually use commit=y and buffer=4000000 (give of take) this way oracle will commit after every 3MB or so. You can make the buffer bigger if you like, that way you will have less frequent commits.
I don't think that commit=y will make the import faster - it will probably slow it down. However it would give you a better chance of the import actually completing successfully without running out of rollback space.