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Diffstat (limited to 'qpid/doc/book/src/java-broker/Java-Broker-Runtime-Flow-To-Disk.xml')
| -rw-r--r-- | qpid/doc/book/src/java-broker/Java-Broker-Runtime-Flow-To-Disk.xml | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/qpid/doc/book/src/java-broker/Java-Broker-Runtime-Flow-To-Disk.xml b/qpid/doc/book/src/java-broker/Java-Broker-Runtime-Flow-To-Disk.xml new file mode 100644 index 0000000000..f2dbb162e1 --- /dev/null +++ b/qpid/doc/book/src/java-broker/Java-Broker-Runtime-Flow-To-Disk.xml @@ -0,0 +1,42 @@ +<?xml version="1.0" encoding="utf-8"?> +<!-- + + 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. + +--> + +<section id="Java-Broker-Runtime-Flow-To-Disk"> + <title>Flow to Disk</title> + <para>Flow to disk limits the amount of heap memory that can be occupied by messages. Once this + limit is reached any new transient messages and all existing transient messages will be + transferred to disk. Newly arriving transient messages will continue to go to the disk until the + cumulative size of all messages falls below the limit once again.</para> + <para>By default the Broker makes 40% of the max available memory for messages. This memory is + divided between all the queues across all virtual hosts defined on the Broker with a percentage + calculated according to their current queue size.</para> + <para>For example if there are two queues, one containing 75MB and the second 100MB messages + respectively and the Broker has 1GB heap memory with the default of 40% available for messages. + The first queue will have a target size of 170MB and the second 230MB. Once 400MB is taken by + messages, messages will begin to flow to disk. New messages will cease to flow to disk when + their cumulative size falls beneath 400MB.</para> + <para>Target queue sizes are refreshed periodically according to the housekeeping cycle.</para> + <para>Flow to disk is configured by Broker context variable + <literal>broker.flowToDiskThreshold</literal>. It is expressed as a size in bytes and defaults + to 40% of the JVM maximum heap size.</para> + <para>TODO: implement log message when flow to disk activates/deactives</para> +</section> |