truncate resets the highwater mark.... delete does not, at least not until
you have done the count... at that point the highwater mark is reset
>From: Walter K <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
>Subject: Delete followed by Select Count(1) - SLOW
>Date: Thu, 16 Aug 2001 13:32:50 -0800
>
>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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>Author: Walter K
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