/*
* Licensed to the Apache Software Foundation (ASF) under one or more contributor license
* agreements. See the NOTICE file distributed with this work for additional information regarding
* copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the License. You may obtain a
* copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package org.apache.geode.cache.server;
import org.apache.geode.cache.CacheCallback;
/**
* A load probe is installed in a cache server to measure the load on the cache server for balancing
* load between multiple cache servers.
*
* <p>
* The getLoad method will be called once per poll interval see
* {@link CacheServer#setLoadPollInterval(long)} The {@link ServerLoad} object returned by the
* getLoad method will be sent to the locator every time the load for this server changes. To
* conserve bandwidth, it's a good idea to round the load calculations so that the load will not be
* sent too frequently.
* </p>
* <p>
* The {@link ServerLoad} object contains two floating point numbers indicating the load on the
* server due to client to server connections and due to subscription connections. When routing a
* connection, the locator will choose the server that has the lowest load.
* </p>
* <p>
* It is generally a good idea to pick a load function where 0 connections corresponds to 0 load.
* The default gemfire load probes return a fraction between 0 and 1, where 0 indicates no load, and
* 1 indicates the server is completely loaded.
* </p>
* <p>
* Because cache servers can be stopped, reconfigured, and restarted, the open and close methods on
* this callback can be called several times. If the same callback object is installed on multiple
* cache servers, open and close will be called once for each cache server.
* </p>
*
* @since GemFire 5.7
*
*/
public interface ServerLoadProbe extends CacheCallback {
/**
* Get the load on this server. This method will be called once every pool interval.
*
* @return The current load on this server.
*/
ServerLoad getLoad(ServerMetrics metrics);
/**
* Signals that a cache server using this load probe has been started.
*/
void open();
/**
* Signals that a cache server using this load probe has been closed.
*/
void close();
}