Reduce permgen use from Groovy scripts

[dakrone]

Groovy scripts seem to be using more permgen than MVEL scripts do, especially when sent dynamically.

It would be nice if we reduce the amount of permgen used by these scripts, or make the permgen space recoverable in the event the script is not used.

[fizx]

This is because the GroovyClassLoader hangs on to every class ever created in its class cache. In benchmarks, I can only load ~500 scripts into a Java7 vm with default permgen settings before OOM/permgen. I can get a few thousand in with Java8.

#!/bin/bash
i=0
while \
curl -m 3 -X POST localhost:9200/_search\?size=0 -d @- <<EOT
{
  "query": {
    "function_score": {
      "query": { "match_all": {} },
      "script_score": {
        "script": "$(echo `date +%s`.$RANDOM)",
        "lang": "groovy"
      }
    }
  }
}
EOT
do 
  i=$((i+1))
  echo
done

echo failed after $i iterations

The following patch works for me for dynamic scripts, and I believe it shouldn't have a downside, because (1) ES has it's own Guava class cache (that actually releases classes), and (2) I can't find a codepath in ES that even indirectly uses the GroovyClassLoader's class cache.

# GroovyScriptEngineService.java#113
+ loader.clearCache();
return loader.parseClass(script, generateScriptName());