extent deallocation question

From: Jeremiah Wilton <jwilton_at_speakeasy.net>
Date: Sun, 28 Oct 2001 13:30:53 -0800
Message-ID: <F001.003B68D4.20011028133517@fatcity.com>

Using dictionary-managed tablespaces, it can sometimes take a very long time to drop or truncate a segment with many tens of thousands of extents, because Oracle takes a long time to update UET$ and FET$.

This can be a serious problem for some people because the session performing the DDL holds the ST enqueue for the duration of the extent deallocation.

During these long extent deallocations, I observe the session performing DDL waiting on IPC with the database writer. Can anyone tell me why these long extent allocations spend the vast majority of their time waiting on DBW0? Does every block in UET$ and FET$ have to get written out before the deallocate can proceed? If so, why?

Using a normal application, I can delete and insert tens of thousands of rows in just a few seconds. What takes Oracle so long with UET$ and FET$?

BTW, this is not a problem that I personally have - it is a purely academic question.

--

Jeremiah Wilton
http://www.speakeasy.net/~jwilton

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Author: Jeremiah Wilton
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