Minor Description
Today stored fields disable bulk merges entirely when index sorting is enabled. However when sorting by low-cardinality fields or when the index sort is correlated with the order in which documents get indexed, we could likely still have efficient bulk merges.
For instance, if you are merging two segments that are sorted on a field that can only take 2 values, one could bulk merge the first half of the first segment, then the first half of the second segment, then the second half of the first segment, and finally the second half of the second segment.
