In CQL a row is considered as present if its row marker is live or it
has any cells live. The 'insert' statement creates a row
marker. Internally Origin handles that by inserting a special cell
whose name shares the prefix with other cells in that row.
One consequence of this way of things is that when we query a column
slice from sstables we will have to read the whole CQL row, even if
not all columns are queried. We won't have to include the data, but we
will need liveness information in order to commute it with other
mutations, so that we can finally determine if the row is live or not.
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