Package oracle.kv

Class Consistency

java.lang.Object
oracle.kv.Consistency
All Implemented Interfaces:
Serializable, oracle.kv.impl.util.FastExternalizable
Direct Known Subclasses:
Consistency.NoneRequired, Consistency.Time, Consistency.Version
public abstract class Consistency extends Object implements oracle.kv.impl.util.FastExternalizable, Serializable
Used to provide consistency guarantees for read operations.

In general, read operations may be serviced either at a Master or Replica node. When serviced at the Master node, consistency is always absolute. If absolute consistency is required, ABSOLUTE may be specified to force the operation to be serviced at the Master. For other types of consistency, when the operation is serviced at a Replica node, the transaction will not begin until the consistency policy is satisfied.

The Consistency is specified as an argument to all read operations, for example, get.

See Also:

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static class 
    Consistency.NoneRequired
     
    static class 
    Consistency.Time
    A consistency policy which describes the amount of time the Replica is allowed to lag the Master.
    static class 
    Consistency.Version
    A consistency policy which ensures that the environment on a Replica node is at least as current as denoted by the specified Key-Value pair Consistency.Version.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final Consistency
    ABSOLUTE
    A consistency policy that requires that a transaction be serviced on the Master so that consistency is absolute.
    static final Consistency
    NONE_REQUIRED
    A consistency policy that lets a transaction on a replica using this policy proceed regardless of the state of the Replica relative to the Master.
    static final Consistency
    NONE_REQUIRED_NO_MASTER
    Deprecated.
    as of 4.3, use NONE_REQUIRED or read zones instead

  • Method Summary

    Modifier and Type
    Method
    Description
    static Consistency
    fromByteArray(byte[] keyBytes)
    Deserializes the given bytes that were returned earlier by toByteArray() and returns the resulting Consistency.
    abstract String
    getName()
    Returns the name used to identify the policy.
    byte[]
    toByteArray()
    Returns this Consistency as a serialized byte array, such that fromByteArray(byte[]) may be used to reconstitute the Consistency.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    Methods inherited from interface oracle.kv.impl.util.FastExternalizable

    deserializedForm, writeFastExternal

  • Field Details

    • NONE_REQUIRED

      public static final Consistency NONE_REQUIRED
      A consistency policy that lets a transaction on a replica using this policy proceed regardless of the state of the Replica relative to the Master.

    • ABSOLUTE

      public static final Consistency ABSOLUTE
      A consistency policy that requires that a transaction be serviced on the Master so that consistency is absolute.

    • NONE_REQUIRED_NO_MASTER

      @Deprecated public static final Consistency NONE_REQUIRED_NO_MASTER
      Deprecated.
      as of 4.3, use NONE_REQUIRED or read zones instead
      A consistency policy that requires that a read operation be serviced on a replica; never the Master. When this consistency policy is used, the read operation will not be performed if the only node available is the Master.

      For read-heavy applications (ex. analytics), it may be desirable to reduce the load on the master by restricting the read requests to only the replicas in the store. It is important to note however, that the secondary zones feature is preferred over this consistency policy as the mechanism for achieving this sort of read isolation. But for cases where the use of secondary zones is either impractical or not desired, this consistency policy can be used to achieve a similar effect; without employing the additional resources that secondary zones may require.

  • Method Details

    • toByteArray

      public byte[] toByteArray()
      Returns this Consistency as a serialized byte array, such that fromByteArray(byte[]) may be used to reconstitute the Consistency. Values returned by calls to this method can be used with current and newer releases, but are not guaranteed to be compatible with earlier releases.

    • fromByteArray

      public static Consistency fromByteArray(byte[] keyBytes)
      Deserializes the given bytes that were returned earlier by toByteArray() and returns the resulting Consistency. Values created with either the current or earlier releases can be used with this method, but values created by later releases are not guaranteed to be compatible.

    • getName

      public abstract String getName()
      Returns the name used to identify the policy.