org.apache.cassandra.thrift
Enum ConsistencyLevel

java.lang.Object
  java.lang.Enum<ConsistencyLevel>
      org.apache.cassandra.thrift.ConsistencyLevel

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable<ConsistencyLevel>, org.apache.thrift.TEnum

public enum ConsistencyLevel
extends java.lang.Enum<ConsistencyLevel>
implements org.apache.thrift.TEnum

The ConsistencyLevel is an enum that controls both read and write behavior based on in your storage-conf.xml. 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 . Of course if latency is more important than consistency then you can use lower values for either or both. Write consistency levels make the following guarantees before reporting success to the client: ANY Ensure that the write has been written once somewhere, including possibly being hinted in a non-target node. ONE Ensure that the write has been written to at least 1 node's commit log and memory table QUORUM Ensure that the write has been written to / 2 + 1 nodes LOCAL_QUORUM Ensure that the write has been written to / 2 + 1 nodes, within the local datacenter (requires NetworkTopologyStrategy) EACH_QUORUM Ensure that the write has been written to / 2 + 1 nodes in each datacenter (requires NetworkTopologyStrategy) ALL Ensure that the write is written to <ReplicationFactor> nodes before responding to the client. Read: ANY Not supported. You probably want ONE instead. ONE Will return the record returned by the first node to respond. A consistency check is always done in a background thread to fix any consistency issues when ConsistencyLevel.ONE is used. This means subsequent calls will have correct data even if the initial read gets an older value. (This is called 'read repair'.) QUORUM Will query all storage nodes and return the record with the most recent timestamp once it has at least a majority of replicas reported. Again, the remaining replicas will be checked in the background. LOCAL_QUORUM Returns the record with the most recent timestamp once a majority of replicas within the local datacenter have replied. EACH_QUORUM Returns the record with the most recent timestamp once a majority of replicas within each datacenter have replied. ALL Queries all storage nodes and returns the record with the most recent timestamp.

Enum Constant Summary

ALL

ANY

EACH_QUORUM

LOCAL_QUORUM

ONE

QUORUM

Method Summary

static ConsistencyLevel	findByValue(int value) Find a the enum type by its integer value, as defined in the Thrift IDL.
int	getValue() Get the integer value of this enum value, as defined in the Thrift IDL.
static ConsistencyLevel	valueOf(java.lang.String name) Returns the enum constant of this type with the specified name.
static ConsistencyLevel[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

ONE

public static final ConsistencyLevel ONE

QUORUM

public static final ConsistencyLevel QUORUM

LOCAL_QUORUM

public static final ConsistencyLevel LOCAL_QUORUM

EACH_QUORUM

public static final ConsistencyLevel EACH_QUORUM

ALL

public static final ConsistencyLevel ALL

ANY

public static final ConsistencyLevel ANY

Method Detail

values

public static ConsistencyLevel[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (ConsistencyLevel c : ConsistencyLevel.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static ConsistencyLevel valueOf(java.lang.String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

java.lang.IllegalArgumentException - if this enum type has no constant with the specified name

java.lang.NullPointerException - if the argument is null

getValue

public int getValue()

Get the integer value of this enum value, as defined in the Thrift IDL.

Specified by:

getValue in interface org.apache.thrift.TEnum

findByValue

public static ConsistencyLevel findByValue(int value)

Find a the enum type by its integer value, as defined in the Thrift IDL.

Returns:

null if the value is not found.