build 1 set b b set c c ---- iter files=(1) first next next ---- b:b c:c . build 2 set d d set f f ---- iter files=(1, 2) first next next next ---- b:b c:c d:d f:f # Test seeks within files. iter files=(1, 2) seek-ge bb next next next ---- c:c d:d f:f . iter files=(1, 2) seek-ge a next next next ---- b:b c:c d:d f:f iter files=(1, 2) seek-ge d next next ---- d:d f:f . iter files=(1, 2) seek-ge f next ---- f:f . iter files=(1, 2) seek-ge ff next ---- . .