We have removed support for the touch command for wiredTiger because the result of the touch command (data:

) is very mmapv1 specific. 'numRanges' corresponds to the number of extents touched into memory for a particular collection.

Since the concept of extents also doesn't exist in RocksDB, the result of the touch command doesn't really make sense. Furthermore, the current implementation of touch within RocksDB just forces all data to go through the block cache once by literally using a RocksDB iterator to read in all the data for a column family (the corresponding one for a collection). This is equivalent to doing a collection scan.

I've discussed this with Matt, Igor, and Siying.