Druid Indexing & Xerces Hell – Loader Constraint Violation

Recently my team mate Vihag came across an java.lang.Linkage error while doing druid indexing with CDH 5.10.2

It was good fun we must say finding out the reason.  hehe taking md5 of class files and comparing and finding out which jar the class is loaded from.


2018-05-11 11:03:04,848 FATAL [main] org.apache.hadoop.mapreduce.v2.app.MRAppMaster: Error starting MRAppMaster
java.lang.LinkageError: loader constraint violation: when resolving overridden method “org.apache.xerces.jaxp.DocumentBuilderImpl.newDocument()Lorg/w3c/dom/Document;” the class loader (instance of org/apache/hadoop/util/ApplicationClassLoader) of the current class, org/apache/xerces/jaxp/DocumentBuilderImpl, and its superclass loader (instance of <bootloader>), have different Class objects for the type org/w3c/dom/Document used in the signature
at org.apache.xerces.jaxp.DocumentBuilderFactoryImpl.newDocumentBuilder(Unknown Source)
at org.apache.hadoop.conf.Configuration.loadResource(Configuration.java:2541)
at org.apache.hadoop.conf.Configuration.loadResources(Configuration.java:2503)
at org.apache.hadoop.conf.Configuration.getProps(Configuration.java:2409)
at org.apache.hadoop.conf.Configuration.get(Configuration.java:1233)
at org.apache.hadoop.yarn.factory.providers.RecordFactoryProvider.getRecordFactory(RecordFactoryProvider.java:49)
at org.apache.hadoop.mapreduce.TypeConverter.<clinit>(TypeConverter.java:62)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster$1.call(MRAppMaster.java:481)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster$1.call(MRAppMaster.java:469)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.callWithJobClassLoader(MRAppMaster.java:1579)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.createOutputCommitter(MRAppMaster.java:469)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.serviceInit(MRAppMaster.java:391)
at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster$4.run(MRAppMaster.java:1537)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1920)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.initAndStartAppMaster(MRAppMaster.java:1534)
at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.main(MRAppMaster.java:1467)
2018-05-11 11:03:04,851 INFO [main] org.apache.hadoop.util.ExitUtil: Exiting with status 


Vihag has documented the resolution nicely here @ github


The crux of the matter was that The class ‘DocumentBuilderImpl‘ was present in Druid in the xercesImpl-2.9.1.jar and Yarn was loading it from xercesImpl-2.10.0.jar.

So we removed 2.9.1 jar from druid and replaced it with 2.10.0 jar

Also we noticed that 2.10 jar plays well with xml-apis-1.4.01.jar & not xml-apis-1.3.04.jar

Hope this helps you.






Druid Segment Diskspace Calculator

Recently i have been working with Druid & was trying to come up with the disk space sizing on the historical nodes, as we have to deploy onto remote customer locations, for which we need to come up with machine requests way in advance.


This took me into the world of bitmaps : concise and roaring.

Druid uses concise bitmaps by default and has the option for roaring too.


So after reading a bit i decided to come up with a calculator for Druid Segment Sizing needed on the druid HISTORICAL nodes assuming Concise is used.

You can find the calculator  @ github.com/jaihind213/druid-calculator

PS: Initially i wanted to write a blog post explaining the logic behind my calculator, but was too lazy, so wrote code and included the rationale in the code comments. 🙂

Thank you and hope you find it useful. Feedback is welcome.