Stellar Benchmarks

The utility can be executed via maven using the `exec` plugin, like so, from the `metron-common` directory:

mvn -DskipTests clean package && \
mvn exec:java -Dexec.mainClass="org.apache.metron.common.stellar.benchmark.StellarMicrobenchmark" -Dexec.args="..."

where exec.args can be one of the following:

    -e,--expressions <FILE>   Stellar expressions
    -h,--help                 Generate Help screen
    -n,--num_times <NUM>      Number of times to run per expression (after
                              warmup). Default: 1000
    -o,--output <FILE>        File to write output.
    -p,--percentiles <NUM>    Percentiles to calculate per run. Default:
                              50.0,75.0,95.0,99.0
    -v,--variables <FILE>     File containing a JSON Map of variables to use
    -w,--warmup <NUM>         Number of times for warmup per expression.
                              Default: 100

For instance, to run with a set of Stellar expression in file /tmp/expressions.txt:

```
 # simple functions
 TO_UPPER('john')
 TO_LOWER(name)
 # math functions
 1 + 2*(3 + int_num) / 10.0
 1.5 + 2*(3 + double_num) / 10.0
 # conditionals
 if ('foo' in ['foo']) OR one == very_nearly_one then 'one' else 'two'
 1 + 2*(3 + int_num) / 10.0
 #Network funcs
 DOMAIN_TO_TLD(domain)
 DOMAIN_REMOVE_SUBDOMAINS(domain)

And variables in file /tmp/variables.json:

{
  "name" : "john",
  "int_num" : 1,
  "double_num" : 17.5,
  "one" : 1,
  "very_nearly_one" : 1.000001,
  "domain" : "www.google.com"
}

Written to file /tmp/output.txt would be the following command:

mvn -DskipTests clean package && \
mvn exec:java -Dexec.mainClass="org.apache.metron.common.stellar.benchmark.StellarMicrobenchmark" \
-Dexec.args="-e /tmp/expressions.txt -v /tmp/variables.json -o ./output.json"