12-16-2008
SAP swap recommendations
Hello all.
My company is installing an SAP ERP financials. The consultants are asking me to allocate 30Gbytes of swap. This is on a dedicated Linux box running Redhat 5 64Bit OS. It has 16GB of RAM.I have asked for an explanation but all I'm getting is that this is what SAP recommends. It seems really strange. Redhat recommends 1/3 times RAM for swap on RHEL5. I am seeing virtually no swapping going on. It seems to me if they need this much swap I should be adding RAM. My experience from way back it that too much swap on a linux box can cause problems. This was back in 2002 or so but I'm sure we were seeing really bad performance with too much swap that went away once we reduced it to 2GB of swap only.
My question is simple. Anyone out there running SAP with less swap than RAM? If so, are you experiencing and real problems?
Thanks.
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LEARN ABOUT FREEBSD
kvm_getswapinfo
KVM_SWAPINFO(3) BSD Library Functions Manual KVM_SWAPINFO(3)
NAME
kvm_getswapinfo -- return swap summary statistics for the system
LIBRARY
Kernel Data Access Library (libkvm, -lkvm)
SYNOPSIS
#include <kvm.h>
int
kvm_getswapinfo(kvm_t *kd, struct kvm_swap *, int maxswap, int flags);
DESCRIPTION
The kvm_getswapinfo() function fills an array of kvm_swap structures with swap summary information for each swap device, for up to maxswap -
1 devices. The number of devices, up to maxswap - 1, is returned. A grand total of all swap devices (including any devices that go beyond
maxswap - 1) is returned in one additional array entry. This entry is not counted in the return value. Thus, if you specify a maxswap value
of 1, the function will typically return the value 0 and the single kvm_swap structure will be filled with the grand total over all swap
devices. The grand total is calculated from all available swap devices whether or not you made room for them all in the array. The grand
total is returned.
The flags argument is currently unused and must be passed as 0.
If an error occurs, -1 is returned.
Each swap partition and the grand total is summarized in the kvm_swap structure. This structure contains the following fields:
char ksw_devname[];
int ksw_total;
int ksw_used;
int ksw_flags;
Values are in PAGE_SIZE'd chunks (see getpagesize(3)). ksw_flags contains a copy of the swap device flags.
CACHING
This function caches the nlist values for various kernel variables which it reuses in successive calls. You may call the function with kd ==
NULL to clear the cache.
DIAGNOSTICS
If the load average was unobtainable, -1 is returned; otherwise, the number of swap devices actually retrieved is returned.
If the name of the swap device does not fit in the static char buffer in the structure, it is truncated. The buffer is always zero termi-
nated.
SEE ALSO
kvm(3)
BSD
January 22, 1999 BSD