Messages in this thread |  | | Date | Fri, 03 Nov 2000 23:39:52 -0800 | From | Josue Emmanuel Amaro <> | Subject | Re: Value of TASK_UNMAPPED_SIZE on 2.4 |
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All,
Additional follow up.
The idea of modifying this variable is to increase the amount of memory that a process can use. A database like Oracle can benefit from this because it allows Oracle to create a bigger data buffer.
An obvious side effect of allocating more physical memory to a process is that there is less available for other things like the kernel buffer cache. This brings up a question. Would a write of a data block from the Oracle data buffer incur a "read penalty" if the block is not in the buffer cache?
For example, a data block is read by Oracle into its buffer. Since it is read through the file system, this block is now present in the buffer cache too. After a while, and since we have allocated most of the memory to Oracle, that block is removed/replaced from the cache.
Now a transaction modifies that block in Oracle's buffer and Oracle writes it to disk. Does the kernel firsts reads that block into the buffer cache, "read penalty", and then writes it to disk? Or does it just write through the buffer cache now placing the block in the kernel buffer cache?
Regards,
-- ======================================================================= Josue Emmanuel Amaro Josue.Amaro@oracle.com Linux Products Manager Phone: 650.506.1239 Intel and Linux Technologies Group Fax: 650.413.0167 =======================================================================
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