That depends on what someone is willing to compromise. Extra space to point back at exactly that key (but that also needs to be updated each compaction?); pers

That depends on what someone is willing to compromise. Extra space to point back at exactly that key (but that also needs to be updated each compaction?); personally I'd normally rather pay the lookup or key sort on iterator snapshot fee. An 'insert, or re-sorted order' side index which allows for nodes to be marked as 'deleted' (maybe nil / null, maybe a sentinel value meaning skip?); I might propose that to see if it fit the requirements well enough.