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Oracle KEEP Pool

Oracle Tips by Burleson Consulting

Automatically Generate KEEP Syntax

A DBA can easily write a script that automatically identifies candidates for the KEEP pool and generates the syntax to move the tables into the pool.  The placement criteria for tables and indexes into the KEEP buffer are straightforward:

§       Frequently accessed tables: The threshold for access can be adjusted in the script.

§       High buffer residency: Any table that has more than 80% of its blocks in the data buffer should be cached in the KEEP pool.

The approach to identifying tables for the KEEP pool is simple.  All objects that have more than 80% of their data blocks in the buffer should be assigned to the KEEP pool.  The following section contains scripts for each of these methods.

Automating the Assignment of KEEP Pool Contents

Another method for identifying tables and indexes for the KEEP pool involves the examination of the current blocks in the data buffer.   For the buf_keep_pool.sql query, the rules are simple. 

§       Use the KEEP pool if the object consumes more than 10% of the total size of the data buffer.

§       Use the KEEP pool if more than 50% of the objects blocks already resides in the data buffer, according to an x$bh query.

It is highly unlikely that an undeserving table or index would meet this criterion.  Of course, this script would need to be run at numerous times during the day because the buffer contents change very rapidly.


The following script can be run every hour via dbms_job and will automate the monitoring of KEEP pool candidates.  Every time it finds a candidate, the DBA will execute the syntax and adjust the total KEEP pool size to accommodate the new object.


§       buf_keep_pool.sql


-- *************************************************

-- Copyright © 2005 by Rampant TechPress

-- This script is free for non-commercial purposes

-- with no warranties.  Use at your own risk.


-- To license this script for a commercial purpose,

-- contact info@rampant.cc

-- *************************************************


set pages 999


set lines 92



spool keep_syn.lst


drop table t1;


create table t1 as


   o.owner          owner,

   o.object_name    object_name,

   o.subobject_name subobject_name,

   o.object_type    object_type,

   count(distinct file# || block#)         num_blocks


   dba_objects  o,

   v$bh         bh


   o.data_object_id  = bh.objd


   o.owner not in ('SYS','SYSTEM')


   bh.status != 'free'

group by





order by

   count(distinct file# || block#) desc




   'alter '||s.segment_type||' '||t1.owner||'.'||s.segment_name||' storage (buffer_pool keep);'



   dba_segments s


   s.segment_name = t1.object_name


   s.owner = t1.owner


   s.segment_type = t1.object_type


   nvl(s.partition_name,'-') = nvl(t1.subobject_name,'-')


   buffer_pool <> 'KEEP'


   object_type in ('TABLE','INDEX')

group by





   (sum(num_blocks)/greatest(sum(blocks), .001))*100 > 80




spool off;


The following is sample of the output from this script.


alter TABLE BOM.BOM_DELETE_SUB_ENTITIES storage (buffer_pool keep);

alter TABLE BOM.BOM_OPERATIONAL_ROUTINGS storage (buffer_pool keep);

alter INDEX BOM.CST_ITEM_COSTS_U1 storage (buffer_pool keep);

alter TABLE APPLSYS.FND_CONCURRENT_PROGRAMS storage (buffer_pool keep);

alter TABLE APPLSYS.FND_CONCURRENT_REQUESTS storage (buffer_pool keep);

alter TABLE GL.GL_JE_BATCHES storage (buffer_pool keep);

alter INDEX GL.GL_JE_BATCHES_U2 storage (buffer_pool keep);

alter TABLE GL.GL_JE_HEADERS storage (buffer_pool keep);

alter TABLE INV.MTL_DEMAND_INTERFACE storage (buffer_pool keep);

alter INDEX INV.MTL_DEMAND_INTERFACE_N10 storage (buffer_pool keep);

alter TABLE INV.MTL_ITEM_CATEGORIES storage (buffer_pool keep);

alter TABLE INV.MTL_ONHAND_QUANTITIES storage (buffer_pool keep);

alter TABLE INV.MTL_SUPPLY_DEMAND_TEMP storage (buffer_pool keep);

alter TABLE PO.PO_REQUISITION_LINES_ALL storage (buffer_pool keep);

alter TABLE AR.RA_CUSTOMER_TRX_ALL storage (buffer_pool keep);

alter TABLE AR.RA_CUSTOMER_TRX_LINES_ALL storage (buffer_pool keep);

alter INDEX WIP.WIP_REQUIREMENT_OPERATIONS_N3 storage (buffer_pool keep);


In sum, there are two ways to identify tables and indexes for full caching in the KEEP pool.  The first step is to explain all of the SQL in the databases that are looking for small-table, full-table scans.  Next, the data buffer cache should be examined repeatedly in order to identify any objects that have more than 80% of their blocks in RAM.  The next section covers how the job is finished and how the KEEP pool can be resized to accommodate the new objects.



This is an excerpt from my latest book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 50%-off and get instant access to the code depot of Oracle tuning scripts:



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