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The "API" page has been changed by jeremyhanna. http://wiki.apache.org/cassandra/API?action=diff&rev1=16&rev2=17 -------------------------------------------------- == Structures == === ConsistencyLevel === - The `ConsistencyLevel` is an `enum` that controls both read and write behavior based on `<ReplicationFactor>` schema definition. The different consistency levels have different meanings, depending on if you're doing a write or read operation. Note that if `W` + `R` > `ReplicationFactor`, where W is the number of nodes to block for on write, and R the number to block for on reads, you will have strongly consistent behavior; that is, readers will always see the most recent write. Of these, the most interesting is to do `QUORUM` reads and writes, which gives you consistency while still allowing availability in the face of node failures up to half of `ReplicationFactor`. Of course if latency is more important than consistency then you can use lower values for either or both. + The `ConsistencyLevel` is an `enum` that controls both read and write behavior based on `<ReplicationFactor>` in your schema definition. The different consistency levels have different meanings, depending on if you're doing a write or read operation. Note that if `W` + `R` > `ReplicationFactor`, where W is the number of nodes to block for on write, and R the number to block for on reads, you will have strongly consistent behavior; that is, readers will always see the most recent write. Of these, the most interesting is to do `QUORUM` reads and writes, which gives you consistency while still allowing availability in the face of node failures up to half of `ReplicationFactor`. Of course if latency is more important than consistency then you can use lower values for either or both. All discussion of "nodes" here refers to nodes responsible for holding data for the given key; "surrogate" nodes involved in HintedHandoff do not count towards achieving the requested !ConsistencyLevel.
