projectionValidation(inputFields);
// replaces normal aggregation here with a global grouping because it needs to be consistent across batches
return new ChainedAggregatorDeclarer(this, new GlobalAggScheme())
.aggregate(inputFields, agg, functionFields)
.chainEnd()
.partitionPersist(spec, functionFields, new CombinerAggStateUpdater(agg), functionFields);
}