EXP, consistent=y equals large rollback segs, why?
Re: Export utility and option CONSISTENT
http://download-west.oracle.com/docs...ch01.htm#20622
Extract:
If you use CONSISTENT=Y and the volume of updates is large, the rollback segment will be large. In addition, the export of each table will be slower because the rollback segment must be scanned for uncommitted transactions.
I don't understand why the rollback seg should be large since if CONSISTENT=Y this should block changes taking place on the relevant nested/partitioned table until that table has been exported. Or are these changes put on hold/queued and then applied immediately after the export of the relevant object. Perhaps someone could clarify.
:confused:
Gus
Re: EXP, consistent=y equals large rollback segs, why?
CONSISTENT=Y triggers Oracle to run SET TRANSACTION READ ONLY before exporting every single table or a partition of a table. That's all. Thus, for partitioned tables, even CONSISTENT=Y will not garantee that export is consistent.
Re: Re: EXP, consistent=y equals large rollback segs, why?
Quote:
Originally posted by julian
CONSISTENT=Y triggers Oracle to run SET TRANSACTION READ ONLY before exporting every single table or a partition of a table. That's all. Thus, for partitioned tables, even CONSISTENT=Y will not garantee that export is consistent.
I believe that it's "serializable",not "read only".
Re: Re: Re: EXP, consistent=y equals large rollback segs, why?
Quote:
Originally posted by slimdave
I believe that it's "serializable",not "read only".
It's READ ONLY, not SERIALIZABLE.
SET TRANSACTION READ ONLY does two things, it inititiates a transaction, and it assigns a start SCN for the transaction. That start SCN will be used for any query executed in the course of the transaction.