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6.2. Checking Swap Space Size and Usage
You can check the size and current usage of swap space by running the command:
grep SwapTotal /proc/meminfo
Swap usage may slowly increase as shown above but should stop at some point. If swap usage continues to grow steadily or is already large, then one of the following choices may need to be considered:
- Adding more RAM.
- Reducing the size of the SGA.
- Increasing the size of the swap space.
If you see constant swapping, then you need to either add more RAM or reduce the size of the SGA. Constant swapping should be avoided at all cost. You can check current swap activity using the following commands:
$ vmstat 3 100 procs memory swap io system cpu r b swpd free buff cache si so bi bo in cs us sy id wa 1 0 0 972488 7148 20848 0 0 856 6 138 53 0 0 99 0 0 1 0 962204 9388 20848 0 0 747 0 4389 8859 23 24 11 41 0 1 0 959500 10728 20848 0 0 440 313 1496 2345 4 7 0 89 0 1 0 956912 12216 20848 0 0 496 0 2294 4224 10 13 0 77 1 1 0 951600 15228 20848 0 0 997 264 2241 3945 6 13 0 81 0 1 0 947860 17188 20848 0 0 647 280 2386 3985 9 9 1 80 0 1 0 944932 19304 20848 0 0 705 0 1501 2580 4 9 0 87
The fields si and so show the amount of memory paged in from disk and paged out to disk, respectively. If the server shows continuous swap activity then more memory should be added or the SGA size should be reduced. To check the history of swap activity, you can use the sar command. For example, to check swap activity from Oct 12th:
# ls -al /var/log/sa | grep "Oct 12" -rw-r--r-- 1 root root 2333308 Oct 12 23:55 sa12 -rw-r--r-- 1 root root 4354749 Oct 12 23:53 sar12 # sar -W -f /var/log/sa/sa12 Linux 2.4.21-32.0.1.ELhugemem (rac01prd) 10/12/2005 12:00:00 AM pswpin/s pswpout/s 12:05:00 AM 0.00 0.00 12:10:00 AM 0.00 0.00 12:15:00 AM 0.00 0.00 12:20:00 AM 0.00 0.00 12:25:00 AM 0.00 0.00 12:30:00 AM 0.00 0.00 ...
The fields
pswpin
and pswpout
show the total number of pages brought in and out per second, respectively.
If the server shows sporadic swap activity or swap activity for a short period time at certain intervals, then you can either add more swap space or RAM. If swap usage is already very large, do not confuse very large swap usage with constant swapping, then more RAM is recommended.