Re: What creates the most volume of REDO entries: INSERT, UPDATE, or DELETE?

From: joel garry <>
Date: Fri, 17 Jul 2009 14:50:08 -0700 (PDT)
Message-ID: <>

On Jul 17, 12:39 pm, dana <> wrote:
> Which of these 3 operations creates the most volume of total REDO log
> file entries; not REDO log *records*: INSERT, UPDATE, or DELETE? A
> colleague of mine says INSERTS add more to the redo log file. His
> rationale? the redo log contains all changes to the database; and an
> entire row takes the most redo log file space to store and re-play if
> the database goes down.
> In practice, it seems like DELETEs create larger REDO log files; have
> seen servers crash when archive redo log disk space runs out from
> running DELETE FROMs instead of TRUNCATEs; when the same raw number of
> INSERT operations doesn't seem to cause the same problem.
> The only thing I can come up with: for UNDO, DELETE operations create
> the most UNDO volume because they store the "before" image of a row.
> INSERT operations create the least UNDO volume because they store only
> a ROWID. Seems that UNDO records are mirrored in the redo log files.
> Is this why large numbers of INSERTS seem to be less redo logfile
> intensive than the same number of DELETEs?
> Wondering if I'm missing something about a symmetry or asymmetry
> between INSERTs and DELETEs and the volume of space they fill in the
> redo log files; vs. redo records only.
> Thanks.
> Dana

You're missing the concept of change vectors. The redo is the difference between the block and the new block. If you only change a varchar2(1), not much redo.

See: metalink Note: 1031381.6 or

Google around, there are explanations by people like Tom Kyte somewhere that compare how much redo generated. isn't what I was looking for, but a start.


-- is bogus.
Received on Fri Jul 17 2009 - 16:50:08 CDT

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