We are interested in projecting a subset of fields from the post-image document in a changestream.

Testing showed (also see CLOUDP-91896) that performance only improves when the projection is smaller than some fraction of the total document size (as a function of network delay etc).

When most fields in the document are projected, there could be a 30% slowdown.

Is it possible to optimize changestream projection so that overheads for degenerate cases is minimized? Otherwise it is hard to determine whether or not Search can use this optimization for a certain collection.

Note that in this case, the projection only applies to fields nested under `fullDocument.*`, so it is possible to push the projection down to the query system (by a query optimization or by exposing new APIs)