Eric Sirianni created HDFS-5680:
-----------------------------------
Summary: Double-JSON-encoding of JMX attributes yields malformed
JSON
Key: HDFS-5680
URL: https://issues.apache.org/jira/browse/HDFS-5680
Project: Hadoop HDFS
Issue Type: Bug
Components: datanode, namenode
Reporter: Eric Sirianni
Priority: Minor
The practice of "double JSON encoding" JMX attributes:
# in the {{MXBean}} itself using Jetty's {{JSON.toString(...)}}
# in the {{JMXJsonServlet}} using Jackson
results in malformed JSON documents (technically not "malformed", but doesn't
properly allow for traversal into nested JSON structures).
For example:
{noformat}
$ curl
http://localhost:50070/jmx?get=Hadoop:service=NameNode,name=NameNodeInfo::NodeUsage
{
"beans" : [ {
"name" : "Hadoop:service=NameNode,name=NameNodeInfo",
"modelerType" : "org.apache.hadoop.hdfs.server.namenode.FSNamesystem",
"NodeUsage" :
"{\"nodeUsage\":{\"min\":\"0.00%\",\"median\":\"0.01%\",\"max\":\"0.01%\",\"stdDev\":\"0.00%\"}}"
} ]
{noformat}
The {{NodeUsage}} attribute should instead be:
{noformat}
"NodeUsage" :
{"nodeUsage":{"min":"0.00%","median":"0.01%","max":"0.01%","stdDev":"0.00%"}}
{noformat}
The Web UI seems to be aware of this and has applied a workaround:
{code:title=dfshealth.js}
// Workarounds for the fact that JMXJsonServlet returns non-standard JSON
strings
{code}
Putting JMX aside, one fix would be to let {{JMXJsonServlet}} do all the
encoding and simply have the {{MXBean}} return a {{Map}}. That would, however,
likely not encode properly for native JMX access. I'm not familiar enough with
how JMX is used elsewhere in Hadoop to suggest an alternative.
--
This message was sent by Atlassian JIRA
(v6.1.4#6159)
