Compiler hints for new java api

[fhueske]

We need a very good integration of optimizer hints with the API. In production settings, SQL queries are very often hand-tuned. We should give the possibility to allow that for Stratosphere Jobs as well.

Hints include:

• Data and UDF hints, e.g., cardinality, data size, output ratio
• Plan hints, e.g., local and shipping strategies

In addition we need a good plan visualization tool, but that's a separate issue.

[rmetzger]

How about a CompilerHint class?

CompilerHint hint = new CompilerHint();
hint.setOutputRatio(0.5);
hint.setPreservesOrder(true);
DataSet<String> a;
b = a.map(new SuperMapper(), hint);