public bool TryMergeWith(MapReduceJob next, out MapReduceJob combined)
{
// we can merge any two jobs with the first having phases i .. j and the second having phases j .. k
if (this.Phases.Max() <= next.Phases.Min())
{
combined = this.Merge(
next,
mapExpression: Merge(this.MapExpression, next.MapExpression),
combineExpression: Merge(this.CombineExpression, next.CombineExpression),
reduceExpression: Merge(this.ReduceExpression, next.ReduceExpression)
);
return true;
}
// we can also push map-only jobs back onto the output of reduce jobs
if (this.Phases.Contains(Phase.Reduce) && next.Phases.SequenceEqual(new[] { Phase.Map }))
{
combined = this.Merge(
next,
mapExpression: this.MapExpression,
combineExpression: this.CombineExpression,
reduceExpression: Merge(this.ReduceExpression, next.MapExpression)
);
return true;
}
combined = null;
return false;
}
private MapReduceJob Merge(MapReduceJob next,
LambdaExpression mapExpression,
LambdaExpression combineExpression,
LambdaExpression reduceExpression)
{
var mergedJob = new MapReduceJob(
this.OutputParameterExpression.Name + "=>" + next.OutputParameterExpression.Name,
mapExpression: mapExpression,
combineExpression: combineExpression,
reduceExpression: reduceExpression
);
return mergedJob;
}