Re: Nologging clause
- From: Jared Still <jkstill@xxxxxxxxx>
- To: Mark.Bobak@xxxxxxxxxxxx
- Date: Wed, 1 Apr 2009 11:31:41 -0700
On Wed, Apr 1, 2009 at 11:20 AM, Bobak, Mark <Mark.Bobak@xxxxxxxxxxxx>wrote:
> Bill,
>
> No, updates and deletes will *always* log. If you think about how direct
> path works, and why it's restricted to the operations it's restricted to, it
> sort of makes sense. Without getting into all the gory details, direct path
> can do nologging and get away with it, cause when it's doing inserts, it's
> doing them into brand new, never before used blocks, that do *not* already
> contain data. Therefore, rollback is simply a de-allocation of those blocks
> from the segment. In the case of 'delete from tab1 where col_a = 32;',
> well, what if the affected block has rows w/ col_a values of 30-39 in it?
> You're *only* deleting the row where col_a = 32. So, the remaining data in
> the block *must* be protected by redo! If you do a direct path insert, do a
> million inserts, all those rows are guaranteed to be inserted into freshly
> allocated empty blocks, so, "rollback" consists of simply de-allocating
> those blocks. There are no other rows in the block that would get caught up
> in the roll
> back and lost.
>
Which also explains why no-logging INSERTs must include the APPEND hint.
Jared
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