Query service provides users with a query execution plan which includes details like time spent in each phase of query execution. It includes total time spent in index scan. It will be useful if more timing details for index scan are provided as a part of the report.
Possible list of metrics reported can be a follows
1. Total scan duration on indexer side
2. Total scan wait duration on indexer side - including/excluding fetchseqnos.
3. Total scan duration on query client side
4. Total scan wait duration on query client side - including backfill file reading
5. Total disk read duration on indexer side
6. Total duration of scatter/gather per partitioned index on indexer as well as on client side.
7. Total scan duration for group by and aggregate phase.
This will require protocol change with query service, between indexer and query client, and with index storage.