I am an Apigee newbie.

I am trying to understand the Spike Arrest policy.

I am looking at this documentation:

<http://apigee.com/docs/api-services/content/shield-apis-using-spikearrest>

<http://apigee.com/docs/api-services/content/policy-attachment-and-enforcement>

The one thing I cannot understand for certain is if, when the Spike Arrest Policy is applied to an ApiProxy, whether the rate limit is applied per Key/Client Dev Application, or is it shared between all Keys/Client Dev Applications? 

For example if we have the following config:

```
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <SpikeArrest async="false" continueOnError="false" enabled="true" name="spikearrest-1">
  <DisplayName>SpikeArrest-1</DisplayName>
  <FaultRules/>
  <Properties/>
  <Identifier ref="request.header.some-header-name"/>
  <MessageWeight ref="request.header.weight"/>
  <Rate>50ps</Rate>
</SpikeArrest>

```

And Client Dev Apps:  

`1. DevApp1`  

`2. DevApp2`

Is the 50ps rate limit shared between `DevApp1` and `DevApp2`, or do `DevApp1` and `DevApp2` get 50ps rate limit each?

Thanks,