com.adobe.acs.commons.throttling

Class RequestThrottler

java.lang.Object

com.adobe.acs.commons.throttling.RequestThrottler

All Implemented Interfaces:

javax.servlet.Filter

public class RequestThrottler
extends Object
implements javax.servlet.Filter

Allows to throttle certain requests, that means limit the amount of requests matching some path criteria per minute. The primary goal of this implementation is to prevent that some requests are eating up all available CPUs, while others (more important) requests will be impacted by this behavior. This implementation should be activating itself by detecting such situations and start throttling requests. A simple usecase for this can be to limit the number if incoming replication requests and allow more "other" requests be handled. Requests which are supposed to handled by this implementation must match one of the configured regular expressions in

 filtered_paths
 

. Other requests are not considered at all by the throttling implementation. The throttling algorithm is loosely based on the leaky bucket approach, but it allows to adjust the throttling based on CPU load. This means:

• If the CPU usage is smaller than

   start_throttling_percentage
   

  , than no throttling is active at all. If you set this value to "0", throttling will always be active.
• If the CPU usage is higher than the configured

   start_throttling_percentage
   

  , the throttling algorithm is used. It permits at maximum

   max_requests_per_minute
   

  requests per minute to pass, all other requests will be throttled.

The number of requests which are permitted to pass the throttling approach, is determined solely by CPU load; this number starts at the configured maximum (

 max_requests_per_minute
 

and decreases linearly as the CPU usages increases. At 100% usage the number of permitted requests is 0 (zero) and all requests (matching the expression in

 filtered_paths
 

are throttled. This implementation supports 2 modes of throttling:

• rejecting the request with a configurable HTTP statuscode; is should be used in cases when the client is able to handle this case.
• Or blocking the request unless it can be handled. This is transparent for the client (the request might time out, though!), but it blocks this requests for the complete time, which might lead to a shortage of threads.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	RequestThrottler.Config

Constructor Summary

Constructors

Constructor and Description
RequestThrottler()

Method Summary

Modifier and Type	Method and Description
protected void	activate(RequestThrottler.Config c)
protected void	delay(long ms)
void	destroy()
void	doFilter(javax.servlet.ServletRequest request, javax.servlet.ServletResponse response, javax.servlet.FilterChain chain)
protected void	doFilterInternal(org.apache.sling.api.SlingHttpServletRequest req, org.apache.sling.api.SlingHttpServletResponse res)
void	init(javax.servlet.FilterConfig arg0)
protected boolean	needsFiltering(String path)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RequestThrottler

public RequestThrottler()

Method Detail

activate

protected void activate(RequestThrottler.Config c)

doFilter

public void doFilter(javax.servlet.ServletRequest request,
                     javax.servlet.ServletResponse response,
                     javax.servlet.FilterChain chain)
              throws IOException,
                     javax.servlet.ServletException

Specified by:

doFilter in interface javax.servlet.Filter

Throws:

IOException

javax.servlet.ServletException

doFilterInternal

protected void doFilterInternal(org.apache.sling.api.SlingHttpServletRequest req,
                                org.apache.sling.api.SlingHttpServletResponse res)
                         throws IOException

Throws:

IOException

needsFiltering

protected boolean needsFiltering(String path)

delay

protected void delay(long ms)

init

public void init(javax.servlet.FilterConfig arg0)
          throws javax.servlet.ServletException

Specified by:

init in interface javax.servlet.Filter

Throws:

javax.servlet.ServletException

destroy

public void destroy()

Specified by:

destroy in interface javax.servlet.Filter