As described in cockroachdb/cockroach#85364, cockroach will need to ingest snapshot SSTs containing a RANGEKEYDEL to clear any existing range keys. A lazy-combined iterator that encounters one of these sstables with RANGEKEYDELs will trigger a switch to combined iteration.

If table stats collected enough information to know that a table only contains RANGEKEYDELs or RANGEKEYUNSETs, the levelIter could avoid triggering combined iteration until a table containing a RANGEKEYSET is observed.