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From aljos...@apache.org
Subject [2/2] flink git commit: [FLINK-7669] Add ClassLoader resolution order to classloader doc
Date Wed, 25 Oct 2017 13:57:46 GMT
[FLINK-7669] Add ClassLoader resolution order to classloader doc


Project: http://git-wip-us.apache.org/repos/asf/flink/repo
Commit: http://git-wip-us.apache.org/repos/asf/flink/commit/3bbff97b
Tree: http://git-wip-us.apache.org/repos/asf/flink/tree/3bbff97b
Diff: http://git-wip-us.apache.org/repos/asf/flink/diff/3bbff97b

Branch: refs/heads/master
Commit: 3bbff97b7e86a361fb77e8b243417fa5e1c60b7a
Parents: 2d88ab8
Author: Aljoscha Krettek <aljoscha.krettek@gmail.com>
Authored: Mon Oct 23 17:05:57 2017 +0200
Committer: Aljoscha Krettek <aljoscha.krettek@gmail.com>
Committed: Wed Oct 25 15:56:21 2017 +0200

----------------------------------------------------------------------
 docs/monitoring/debugging_classloading.md | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/flink/blob/3bbff97b/docs/monitoring/debugging_classloading.md
----------------------------------------------------------------------
diff --git a/docs/monitoring/debugging_classloading.md b/docs/monitoring/debugging_classloading.md
index 4f57c10..414eef6 100644
--- a/docs/monitoring/debugging_classloading.md
+++ b/docs/monitoring/debugging_classloading.md
@@ -57,10 +57,22 @@ YARN classloading differs between single job deployments and sessions:
 
 **Mesos**
 
-Mesos setups following [this documentation](../ops/deployment/mesos.html) currently behave
very much like the a 
+Mesos setups following [this documentation](../ops/deployment/mesos.html) currently behave
very much like the a
 YARN session: The TaskManager and JobManager processes are started with the Flink framework
classes in classpath, job
 classes are loaded dynamically when the jobs are submitted.
 
+## Configuring ClassLoader Resolution Order
+
+Flink uses a hierarchy of ClassLoaders for loading classes from the user-code jar(s). The
user-code
+ClassLoader has a reference to the parent ClassLoader, which is the default Java ClassLoader
in most
+cases. By default, Java ClassLoaders will first look for classes in the parent ClassLoader
and then in
+the child ClassLoader for cases where we have a hierarchy of ClassLoaders. This is problematic
if you
+have in your user jar a version of a library that conflicts with a version that comes with
Flink. You can
+change this behaviour by configuring the ClassLoader resolution order via
+`classloader.resolve-order: child-first` in the Flink config. However, Flink classes will
still
+be resolved through the parent ClassLoader first, although you can also configure this via
+`classloader.parent-first-patterns` (see [config](../ops/config.html))
+
 
 ## Avoiding Dynamic Classloading
 
@@ -68,11 +80,11 @@ All components (JobManger, TaskManager, Client, ApplicationMaster, ...)
log thei
 They can be found as part of the environment information at the beginning of the log.
 
 When running a setup where the Flink JobManager and TaskManagers are exclusive to one particular
job, one can put JAR files
-directly into the `/lib` folder to make sure they are part of the classpath and not loaded
dynamically. 
+directly into the `/lib` folder to make sure they are part of the classpath and not loaded
dynamically.
 
 It usually works to put the job's JAR file into the `/lib` directory. The JAR will be part
of both the classpath
 (the *AppClassLoader*) and the dynamic class loader (*FlinkUserCodeClassLoader*).
-Because the AppClassLoader is the parent of the FlinkUserCodeClassLoader (and Java loads
parent-first), this should
+Because the AppClassLoader is the parent of the FlinkUserCodeClassLoader (and Java loads
parent-first, by default), this should
 result in classes being loaded only once.
 
 For setups where the job's JAR file cannot be put to the `/lib` folder (for example because
the setup is a session that is


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