Improve concurrency

[codahale]

Figure out a way to make Jackson contend less:

qtp2078619350-199 id=199 state=BLOCKED
    - waiting to lock <0x51cf2096> (a org.codehaus.jackson.map.ser.SerializerCache)
     owned by qtp2078619350-63 id=63
    at org.codehaus.jackson.map.ser.SerializerCache.getReadOnlyLookupMap(SerializerCache.java:49)
    at org.codehaus.jackson.map.ser.StdSerializerProvider.<init>(StdSerializerProvider.java:208)
    at org.codehaus.jackson.map.ser.StdSerializerProvider.createInstance(StdSerializerProvider.java:217)
    at org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:239)
    at org.codehaus.jackson.map.ObjectMapper.writeValue(ObjectMapper.java:1143)
    at org.codehaus.jackson.impl.JsonGeneratorBase.writeObject(JsonGeneratorBase.java:315)
    at com.codahale.jerkson.Generator$class.generate(Generator.scala:38)
    at com.codahale.jerkson.Generator$class.generate(Generator.scala:27)
    at com.codahale.jerkson.Json$.generate(Json.scala:6)