Hi Walter,
The extents you refer to in ur thread is the allocated
space. Oracle by default scans upto the high
watermark. The reason truncate is fast is cause it
resets the high watermark so oracle did not scan
anything for u when it returned 0 rows .. however in
case of delete, it still scanned upto the HWM
Deepak
- Walter K <alden14004_at_yahoo.com> wrote:
> I have a user that deleted all of the rows in a
> table
> (i.e. 100,000), waited for it to complete, and then
> ran a SELECT COUNT(1) FROM <table>. It took a few
> minutes for '0 rows' to be returned to the prompt.
> The
> table has ~60 extents (128k ea.). Granted, the
> number
> of extents is excessive but it's a development
> instance and this table is an exception.
>
> Is Oracle scanning through all of the blocks, since
> the space wasn't released, and this is the cause of
> the latency?
>
> The curious thing is that I told this user to use
> TRUNCATE instead and we talked about using the
> drop/reuse storage clauses. He performed a
> TRUNCATE...REUSE STORAGE and the same select and it
> was night and day in terms of performance. If the
> allocated space isn't being released in this case
> also, why is there such a performance difference
> between the two?
>
> -w
>
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Received on Thu Aug 16 2001 - 15:36:17 CDT
