Delete followed by Select Count(1) - SLOW

From: Walter K <alden14004_at_yahoo.com>
Date: Thu, 16 Aug 2001 13:20:26 -0700
Message-ID: <F001.0036DF9F.20010816133250@fatcity.com>

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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Received on Thu Aug 16 2001 - 15:20:26 CDT