Version: 9.4.20.v20190813 |

Limiting Load
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## Limiting Load

To achieve optimal fair handling for all users of a server, it can be necessary to limit the resources that each user/connection can utilize so as to maximize throughput for the server or to ensure that the entire server runs within the limitations of it’s runtime.

### Low Resources Monitor

An instance of LowResourcesMonitor may be added to a Jetty server to monitor for low resources situations and to take action to limit the number of idle connections on the server. To configure the low resources monitor, you can enable the the `lowresources.mod` on the command line, which has the effect of including the following XML configuration:

    <?xml version="1.0"?><!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure_9_3.dtd">

    <!-- =============================================================== --><!-- Mixin the Low Resources Monitor                                 --><!-- =============================================================== -->

    <Configure id="Server" class="org.eclipse.jetty.server.Server">
      <Call name="addBean">
        <Arg>
          <New id="lowResourceMonitor" class="org.eclipse.jetty.server.LowResourceMonitor">
            <Arg name="server"><Ref refid='Server'/></Arg>
            <Set name="period"><Property name="jetty.lowresources.period" deprecated="lowresources.period" default="1000"/></Set>
            <Set name="lowResourcesIdleTimeout"><Property name="jetty.lowresources.idleTimeout" deprecated="lowresources.lowResourcesIdleTimeout" default="1000"/></Set>
            <Set name="monitorThreads"><Property name="jetty.lowresources.monitorThreads" deprecated="lowresources.monitorThreads" default="true"/></Set>
            <Set name="maxConnections"><Property name="jetty.lowresources.maxConnections" deprecated="lowresources.maxConnections" default="0"/></Set>
            <Set name="maxMemory"><Property name="jetty.lowresources.maxMemory" deprecated="lowresources.maxMemory" default="0"/></Set>
            <Set name="maxLowResourcesTime"><Property name="jetty.lowresources.maxLowResourcesTime" deprecated="lowresources.maxLowResourcesTime" default="5000"/></Set>
            <Set name="acceptingInLowResources"><Property name="jetty.lowresources.accepting" default="true"/></Set>
          </New>
        </Arg>
      </Call>
    </Configure>

The monitor is configured with a period in milliseconds at which it will scan the server looking for a low resources condition, which may be one of:

- If `monitorThreads` is configured as true and a connectors Executor is an instance of ThreadPool, then its `isLowOnThreads()` method is used to detect low resources.
- If `maxConnections` is configured to a number >0 then if the total number of connections from all monitored connectors exceeds this value, then low resources state is entered.
- If the `maxMemory` field is configured to a number of bytes >0 then if the JVMs total memory minus its idle memory exceeds this value, then low resources state is entered.

Once low resources state is detected, then the monitor will iterate over all existing connections and set their `IdleTimeout` to its configured `lowResourcesIdleTimeout` in milliseconds. This allows the idle time of existing connections to be reduced so that the connection is quickly closed if no further request are received.

If the low resources state persists longer than the time in milliseconds configured for the `maxLowResourcesTime` field, the the `lowResourcesIdleTimeout` is repeatedly applied so that new connections as well as existing connections will be limited.

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