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Re: DB Block Buffers - Too Much ???

From: Gaja Krishna Vaidyanatha <>
Date: Wed, 21 Jun 2000 20:21:04 -0700 (PDT)
Message-Id: <>


The answer to your question is yes. One can and should lock the SGA in memory to prevent even preemptive paging (let alone swapping or process deactivation) from occuring on the pages belonging to the SGA. This however should to be done, only after the memory allocation for the SGA is done in a prudent fashion, keeping in mind total memory, memory needed for PGAs (based on sizing of sort_area_size, hash_area_size etc.), and memory needed for the O-S and other applications (if applicable).

Waleed Khedr has already talked about how to do it on Solaris using the USE_ISM parameter, which basically uses an algorithm that "touches" the entries in the page-table periodically, to basically fake usage of all memory pages. There are however a number of bugs logged with respect to this feature on Solaris, so use it after you have determined whether the bug is relevant on your version of Oracle, version of Solaris, and your platform. There were some severe ISM-related bugs on the E-10K platform, so watch out.

On other platforms like HP-UX, you need to grant the MLOCK privilege to dba:oracle by executing the userprivgrp command or something to that effect ( do a man -k priv and you will see the command I am talking about). After granting that privilege, you will then need to set the MLOCK_SGA, LOCK_SGA or relevant parameter in the init.ora. Please check what the actual parameter is on your system - by doing a "show parameter lock" or "show parameter sga" inside svrmgrl.

On some of the systems that I have worked with, I have seen paging and swapping actually drop to negligible levels after locking the SGA in memory. If the memory sizing and allocation for a system is done right, locking the SGA in memory will provide a definite boost to overall system performance.

Hope that helps,


Gaja Krishna Vaidyanatha | Brio Technology | (972)-304-1170

"Opinions and views expressed are my own and not of Brio Technology"

Received on Wed Jun 21 2000 - 22:21:04 CDT

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