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Top Forums UNIX for Advanced & Expert Users Please advise good source of info about swapping Post 302614425 by methyl on Wednesday 28th of March 2012 01:12:31 PM
Old 03-28-2012
1) The O/S will do necessary paging as processes are created and die. If you have no swap, memory will become fragmented.

2) You should never set the swap size to zero because the O/S still needs to shuffle pages around in the background. While you are tuning Oracle you need substantial leeway and I would have swap at least the same size as memory to allow for future expansion, unexpected peaks and configuration mistakes. I'd rather have the system run slow than crash.

Oracle makes extensive use of O/S Shared Memory and you must allow memory for this and build the kernel correctly.

Most unix O/S dedicate 25% of memory to disc buffers by default. You either allow for it or change the kernel parameters. If the system only ever runs Oracle then there is much scope to give memory to Oracle disc buffers.
Many Oracle DBAs don't allocate enough memory for table sorts in the SGA.

There are huge and comprehensive manuals from Oracle regarding sizing and tuning on each different O/S. In my experience Oracle will never run properly straight out of the box.

3) Yes if you have 8Gb RAM and 8Gb swap the most virtual memory you could ever use is 16Gb.
There was a historic requirement to have a minimum swap of the same size as memory and older unix would not let you use any physical memory above that point. There was no mirroring, but swap was also used for dump in the event of a system crash and it had to be big enough. That rule has been relaxed on some modern O/S.
Older unix did indeed recommend creating swap at 2x or even 3x memory and swap was used for storing idle processes on heavily loaded systems (but it was slow if any active processes got displaced into swap).

Last edited by methyl; 03-28-2012 at 02:22 PM..
 

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Glib::Flags(3)						User Contributed Perl Documentation					    Glib::Flags(3)

NAME
Glib::Flags DESCRIPTION
Glib maps flag and enum values to the nicknames strings provided by the underlying C libraries. Representing flags this way in Perl is an interesting problem, which Glib solves by using some cool overloaded operators. The functions described here actually do the work of those overloaded operators. See the description of the flags operators in the "This Is Now That" section of Glib for more info. HIERARCHY
Glib::Flags METHODS
scalar = $class->new ($a) o $a (scalar) Create a new flags object with given bits. This is for use from a subclass, it's not possible to create a "Glib::Flags" object as such. For example, my $f1 = Glib::ParamFlags->new ('readable'); my $f2 = Glib::ParamFlags->new (['readable','writable']); An object like this can then be used with the overloaded operators. scalar = $a->all ($b, $swap) o $b (scalar) o $swap (scalar) ref = $a->as_arrayref integer = $a->bool ($b, $swap) o $b (scalar) o $swap (integer) integer = $a->eq ($b, $swap) o $b (scalar) o $swap (integer) integer = $a->ge ($b, $swap) o $b (scalar) o $swap (integer) scalar = $a->intersect ($b, $swap) o $b (scalar) o $swap (scalar) integer = $a->ne ($b, $swap) o $b (scalar) o $swap (integer) scalar = $a->sub ($b, $swap) o $b (scalar) o $swap (scalar) scalar = $a->union ($b, $swap) o $b (scalar) o $swap (scalar) scalar = $a->xor ($b, $swap) o $b (scalar) o $swap (scalar) SEE ALSO
Glib COPYRIGHT
Copyright (C) 2003-2009 by the gtk2-perl team. This software is licensed under the LGPL. See Glib for a full notice. perl v5.12.1 2010-07-05 Glib::Flags(3)
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