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The "FileFormatDesignDoc" page has been changed by StuHood. http://wiki.apache.org/cassandra/FileFormatDesignDoc?action=diff&rev1=25&rev2=26 -------------------------------------------------- Cassandra also needs to encode metadata about tuples and ranges of tuples in order to represent creation and deletion timestamps. For both value tuples and range tuples, a varying number (depending on value and range type) of timestamps will need to be encoded. + === Types === + + * ''deleted'' - If a range/value has been deleted at any point in time, we need to record that action with timestamps: marking a range/value ''deleted'' indicates that these timestamps exist + * ''standard'' - A standard value has a timestamp to indicate when it was created; a range will be marked standard if it has children (a standard range without children has no reason to exist) + * ''expiring'' - An expiring value has additional timestamps to indicate when it should be garbage collected. Currently, only values may be marked expiring. + * ''null'' - A range or value entry in a chunk that is only a placeholder. For example, if a parent has ranges but no values, a ''null'' value will be inserted in a chunk to indicate to viewers that the parent exists. + === Range Metadata === Range tuples can be encoded in a very similar fashion to the value tuples represented above, except that they always come in pairs. It will likely make sense to store them in a separate blob from the value tuples, since they will bear very little similarity to one another (TODO: need to confirm with an anecdote or two). @@ -203, +210 @@ This example shows a range tombstone for values at level "name1" between 'havarti' and 'muenster': the chunk for the "name1" level stores a pair of range tuples for the 'cheese' parent and nulls are stored for parents without any range metadata. The end result is that the span stores a tombstone from ('cheese', 'havarti', <empty>) to ('cheese', 'muenster', null), where <empty> is the smallest value, and null is the largest value. Note that it is not possible for ranges for a parent to overlap: in this case, the ranges would be resolved such that the intersection was given the winning timestamp, and the two remainders would use their original timestamps. + + ==== Other uses ==== + + In cases where parents are too wide to fit in a single span, range metadata should also be used to indicate how much of a particular parent is present in a given span. ==== Effect of ordering ====
