Re: Export times: affected by size of table or amount of data?

In article <3766c837.7571952_at_news.siol.net>, Jurij Modic <jmodic_at_src.si> writes
>On Tue, 15 Jun 1999 19:20:32 +0100, Andy Hardy
><aph_at_ahardy.demon.co.uk> wrote:
>
>>In article <3769872b.7762822_at_newshost.us.oracle.com>, Thomas Kyte
>><tkyte_at_us.oracle.com> writes
>>>A copy of this was sent to Andy Hardy <aph_at_ahardy.demon.co.uk>
>>>(if that email address didn't require changing)
>>>On Tue, 15 Jun 1999 14:28:29 +0100, you wrote:
>>>
>>>>Hi,
>>>>
>>>>If I declare a 100Mb table with no data, will it export in less time
>>>>than the same table full of data?
>>>>
>>>>I thought that export times were only dependent on the quantity of data
>>>>stored, but my customer is telling me otherwise...
>>>>
>>>>Andy
>>>
>>>it'll depend. If the 100mb table HAD data at some point and was deleted from
>--
>>>we will scan to the high water mark looking for data. export tends to full
>scan
>>>tables -- if a select count(*) against that empty table doesn't come back
>>>immediately -- neither will export.
>>
>>OK. So if the table is set-up with a large initial extent and has ever
>>contained some data, a full scan will be done.
>
>Well, full scan will be performed in any case. The problem is how long
>will it take a full scan to complete. Full scan will scan each and
>every block from the first block of the first extend up to the block
>where the high water mark is set at the moment.
>
>So, if all the data of the huge table has been DELETEd, the full table
>scan will still scan all the blocks up to the HWM, and this might take
>some time. But if the table was TRUNCATEd, it will end
>instantaneously, as the HWM has been reset to the first block of the
>first segment.

Thanks. Is truncate the only way of resetting the HWM?

Andy
--
Andy Hardy. PGP key available on request