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Top Forums UNIX for Advanced & Expert Users Please advise good source of info about swapping Post 302614307 by methyl on Wednesday 28th of March 2012 11:52:16 AM
Old 03-28-2012
There is a substantial Wikipedia on this subject (and links to more articles):
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Quote:
If I have 8Gb RAM and 8Gb swap and an application requests 20Gb will it run out of memory?
No: The request will be refused.
Btw. The old rule that you must have at least as much swap as you have memory does not apply to modern unix.

Many modern unix systems can be configured to use part of memory for swap. This allows the O/S to defragment main memory quickly and quietly.

If you have Oracle, buy enough memory so that it should never swap and be sure that you understand how to size the SGA and PGA and how to measure these sizes using Oracle itself. It is very common to missize the SGA by a factor of 8 or even 16.

Last edited by methyl; 03-28-2012 at 02:20 PM..
 

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remote_nfs_swap(5)						File Formats Manual						remote_nfs_swap(5)

NAME
remote_nfs_swap - enable swapping across NFS VALUES
Default Allowed values DESCRIPTION
This tunable controls adding a NFS filesystem for use as swap. If is set to only local filesystems and devices can be used for swap. If it is set to both local and networked file systems can be used for swap. Historically, this tunable was used in NFS clusters that are no longer supported, but this capability has not yet been removed. Who Is Expected to Change This Tunable? Anyone. Restrictions on Changing Changes to this tunable take effect on the next boot. When Should the Tunable Be Turned On? Almost never. As previously mentioned, this tunable was designed for systems which are not in use today. Only systems with extremely robust NFS capabilities should even consider using NFS for swap. What Are the Side Effects of Turning the Tunable On? If the value is set to and a NFS partition is added as swap, then some kernel memory will be set aside for NFS transactions to the swap file system. The kernel will then use the NFS swap partition just the same as a local file system. If the NFS capabilities of the system are not robust, this could lead to extremely long swap times (both swap in and swap out), and possibly a loss of memory because all the reserved memory and more could be used by NFS (just when memory pressure is high) causing the need for swap. When Should the Tunable Be Turned Off? Unless you are positive that the NFS system can handle the load of being used as swap, and does not have a local file system or disk drive to spare, this tunable should be set to What Are the Side Effects of Turning the Tunable Off? Any previously defined NFS swap filesystems will no longer be allowed. Kernel memory will not be reserved for NFS transactions due to swap. What Other Tunables Should Be Changed at the Same Time? None. WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX. Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun- able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see at AUTHOR
was developed by HP. Tunable Kernel Parameters remote_nfs_swap(5)
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