This summarize all frequent asked questions in using DDF.
* DDF on Yarn
* Java isses
* R issues
1. What DDF is not ?
* DDF is not a database that run SQL.
* DDF is not JUST a RDD.
* DDF is not JUST a layer run on top of Spark.
2. What is good about DDF ?
* DDF doesn't require users to write map(), reduce(), collect(). DDF value is a higher level of abstraction and any time you go one level higher, two things occur: (a) you can do more by saying less,
and (b) you do give up arbitrary flexibility at the lower level. This is high productivity gains for developers.
* DDF is more than just applying analytic functions to big data. It also enables data sharing (collaboration) via URIs.
* DDF is also about providing a uniform API across different engines, of which Spark is only one.
### DDF on Yarn
1. First you need to compile Spark with your Yarn version
You can read instruction [here](http://spark.apache.org/docs/latest/building-with-maven.html)
2. Then build DDF on Spark that you just built.
3. To test the build you can follow ddf-shell in tutorial
### Java issues
1.Q: How do I fix OutOfMemory while building DDF ?
A: DDF uses maven to build project, you can set MAVEN memory to higher values, for example:
2.Q: I don't have Java on my machine, how to install Java 7 on Mac ?
A: Apple and Oracle do not support Java 1.7 out of the box, you need to install manually
3.Q: I have this error JAVA_HOME is not set properly, how to fix that ?
A: You need to set JAVA_HOME properly, for example: ```sh export JAVA_HOME=`/usr/libexec/java_home` ```
4.Q: I saw this error message "You must build DDF's Java core and spark package firstly"
A:You need to build ddf first.
### R issues
1.Q: How to fix ClassNotFound exception while using R-DDF ?
A: R-DDF use rJava to invoke DDF Java class, make sure you're using Java 1.7, R 3.x and you have installed rJava. This error happens mostly on MacOS X.
- First you need to set JAVA PATH properly, in Mac it looks something like this
sh R CMD javareconf -e
- Then export
2.Q: I have this error while running ```R CMD javareconf -e```
> make: llvm-gcc-4.2: No such file or directory
A: This error occurs mostly on MacOSX. It happens because you can't install rJava. Please follow this instruction