Check for thrashing
Davy Durham
pubaddr2 at davyandbeth.com
Wed Oct 5 07:16:14 CEST 2005
Timothy O'Hare wrote:
> You could monitor the CPU load and swap space usage?
>
Yeah, but my question was what values from vmstat would mean that it's
thrashing.. a plugin would seem simple to write to check that
> Guy B. Purcell wrote:
>
>>
>> On Oct 4, 2005, at 19:26, Davy Durham wrote:
>>
>>> Does anyone know of a plugin that can check if a machine is
>>> "thrashing" by which I mean it continues to swap and swap.. because
>>> either there is too little ram, or too many processes running on
>>> the box.
>>
>>
>>
>> I think such a thing would be unnecessary, really: if a box is
>> thrashing (in the canonical sense of that word--something happens
>> that causes it to have to work harder, which slows everything down
>> so jobs pile up, causing it to have to work even harder, and so on
>> in a catch-22 cycle), then the various services on it you're
>> otherwise monitoring will time out because there aren't enough
>> resources of one kind or another to handle the monitor requests.
>>
>>> I would think a vmstat command could tell you that, though it
>>> would need a few seconds to determine. And I'm not sure what
>>> numbers would indicate what a bad amount would be.
>>
>>
>>
>> The actual implementation of such a thing would need to be carefully
>> crafted to work across multiple OSes. IMHO, it's not worth the
>> effort: if a box truly is thrashing, you should know all about it
>> from existing monitors.
>>
>> -Guy
>>
>>
>>
>>
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>
>
>
>
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