It's unclear what should be in BucketSpec and what should be in BucketUnpacker. Recently there was a bug that occurred as a result of this confusion. We should come up with a clear rationale for what should live where (or if they should be combined), and in what situations one should use one or the other.

My general sense was that BucketSpec contains parameters that are specific to the bucket, and that BucketUnpacker would then contain query-specific attributes determined through analysis. But BucketSpec contains computedMetaProjFields which is query-specific, so that doesn't hold.