VMSTAT - Virtual Memory Statistics
Sticking with the theme of performance monitoring, I'm going to cover some of the other utilities used to monitor a system's and network's performance. The vmstat utility gives a server-wide view of performance. vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity. The first report produced gives averages since the last reboot. Additional reports give information on a sampling period of length delay. The process and memory reports are instantaneous.
vmstat 10 5
When this command is ran vmstat will spend 10 seconds gathering data and reports a single line of statistics. This will continue 5 times. At least 5 seconds is needed for good accuracy. Example output(unfortuantly blooger doesn't format the table properly):
procs memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
1 0 22478 1677 0 0 0 0 0 0 188 1380 157 57 32 0 10
1 0 22506 1609 0 0 0 0 0 0 214 1476 186 48 37 0 16
0 0 22498 1582 0 0 0 0 0 0 248 1470 226 55 36 0 9
FIELD DESCRIPTIONS (These field descriptions came straight from the Man pages)
Procs
r: The number of processes waiting for run time.
b: The number of processes in uninterruptable sleep.
w: The number of processes swapped out but otherwise runnable. This
field is calculated, but Linux never desperation swaps.
Memory
swpd: the amount of virtual memory used (kB).
free: the amount of idle memory (kB).
buff: the amount of memory used as buffers (kB).
Swap
si: Amount of memory swapped in from disk (kB/s).
so: Amount of memory swapped to disk (kB/s).
IO
bi: Blocks sent to a block device (blocks/s).
bo: Blocks received from a block device (blocks/s).
System
in: The number of interrupts per second, including the clock.
cs: The number of context switches per second.
CPU
These are percentages of total CPU time.
us: user time
sy: system time
id: idle time
For CPU issues pay attention to the processes in the run queue (procs r), User time (cpu us), System time (cpu sy), & Idle time (cpu id). If the r column is higher than the number of CPU's in the machine adding some more CPU's would help out. From here you can find out what is using your CPU time with TOP.
For Memory Issues pay attention to the scan rate (sr). The scan rate is the pages scanned by the clock algorithm per second. If the scan rate (sr) is continuously over 200 pages per second then there is a memory shortage. Remember that the free column will dwindle down due to memory being used for I/O cache and buffers, this is normal.
These statistics will go a long way to giving you an idea as to how well your system is responding to requests and if there are any bottle necks it will help give clues as to where to start looking for the problem areas. Hopefully in the next couple of days I can also cover the iostat and netstat commands to help give you an overall look at a sytem and how well it is working.
vmstat 10 5
When this command is ran vmstat will spend 10 seconds gathering data and reports a single line of statistics. This will continue 5 times. At least 5 seconds is needed for good accuracy. Example output(unfortuantly blooger doesn't format the table properly):
procs memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
1 0 22478 1677 0 0 0 0 0 0 188 1380 157 57 32 0 10
1 0 22506 1609 0 0 0 0 0 0 214 1476 186 48 37 0 16
0 0 22498 1582 0 0 0 0 0 0 248 1470 226 55 36 0 9
FIELD DESCRIPTIONS (These field descriptions came straight from the Man pages)
Procs
r: The number of processes waiting for run time.
b: The number of processes in uninterruptable sleep.
w: The number of processes swapped out but otherwise runnable. This
field is calculated, but Linux never desperation swaps.
Memory
swpd: the amount of virtual memory used (kB).
free: the amount of idle memory (kB).
buff: the amount of memory used as buffers (kB).
Swap
si: Amount of memory swapped in from disk (kB/s).
so: Amount of memory swapped to disk (kB/s).
IO
bi: Blocks sent to a block device (blocks/s).
bo: Blocks received from a block device (blocks/s).
System
in: The number of interrupts per second, including the clock.
cs: The number of context switches per second.
CPU
These are percentages of total CPU time.
us: user time
sy: system time
id: idle time
For CPU issues pay attention to the processes in the run queue (procs r), User time (cpu us), System time (cpu sy), & Idle time (cpu id). If the r column is higher than the number of CPU's in the machine adding some more CPU's would help out. From here you can find out what is using your CPU time with TOP.
For Memory Issues pay attention to the scan rate (sr). The scan rate is the pages scanned by the clock algorithm per second. If the scan rate (sr) is continuously over 200 pages per second then there is a memory shortage. Remember that the free column will dwindle down due to memory being used for I/O cache and buffers, this is normal.
These statistics will go a long way to giving you an idea as to how well your system is responding to requests and if there are any bottle necks it will help give clues as to where to start looking for the problem areas. Hopefully in the next couple of days I can also cover the iostat and netstat commands to help give you an overall look at a sytem and how well it is working.
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