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SYS.HIST_HEAD$ defrag?

From: Herring Dave - dherri <>
Date: Wed, 22 Aug 2007 06:39:57 -0500
Message-ID: <>


I've noticed that access of SYS.HIST_HEAD$ takes rather long, especially during the drop of an option with hundreds of partitions, hundreds of columns. The table referenced has statistics gathered on it using DBMS_STATS.GATHER_TABLE_STATS(<owner>,<tabname>,estimate=>1,granularity=>'ALL'), which I believe creates 1 row per column per partition, which in this particular table's case consumes 100,000+ entries. A drop of this table takes around 1.5 hrs! The table has around 60,000,000 rows in it.

I've found using event 10046 that nearly all elapsed time is spent removing rows from HIST_HEAD$, one DELETE statement per entry.

My question is, can SYS.HIST_HEAD$ be rebuilt/defragmented somehow? I gathered stats on it to get some info (then deleted those stats), then created a copy of the table with same storage info. The block count dropped 50%.

This is on a database under Tru64 5.1b. The ETL process which drops/recreates this table weekly is not something I can control. So I can't change the object's configuration nor how stats are gathered.

I will add that I've created a BEFORE DDL trigger to check for a DROP of this table. When triggered, a loop runs DBMS_STATS.DROP_COLUMN_STATISTICS per column in the table, which speeds things up to the point of the DROP taking at most .5 hrs.

I'd appreciate any helpful suggestions or experiences with any type of SYS-owned objects related to problems like the above.



David C. Herring, DBA  |   A c x i o m  Delivery Center Organization 630-944-4762 office | 630-430-5988 wireless | 630-944-4989 fax

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Received on Wed Aug 22 2007 - 06:39:57 CDT

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