Value (h2o-core 3.0.0 API)

java.lang.Object
- water.Iced
- - water.Value

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, java.lang.Cloneable, ForkJoinPool.ManagedBlocker, Freezable
```
public final class Value
extends Iced
implements ForkJoinPool.ManagedBlocker
```
The core Value stored in the distributed K/V store, used to cache Plain Old Java Objects, and maintain coherency around the cluster. It contains an underlying byte[] which may be spilled to disk and freed by the MemoryManager, which is the Iced serialized version of the POJO, and a cached copy of the POJO itself.
Requests to extract the POJO from the Value object first try to return the cached POJO. If that is missing, then they will re-inflate the POJO from the Iced byte[]. If that is missing it is only because the byte[] was swapped to disk by the Cleaner. It will be reloaded from disk and then inflated as normal.
The H2O DKV supports the full Java Memory Model coherency but only with Gets and Puts. Normal Java updates to the cached POJO are local-node visible (due to X86 & Java coherency rules) but NOT cluster-wide visible until a Put completes after the update.
By the same token, updates ot the POJO are not reflected in the serialized form nor the disk-spill copy unless a Put is triggered. As long as a local thread keeps a pointer to the POJO, they can update it at will. If they wish to recover the POJO from the DKV at a later time with all updates intact, they must do a final Put after all updates.
Value objects maintain the needed coherency state, as well as any cached copies, plus a bunch of utility & convenience functions.

See Also:
Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`Key`	`_key` The Key part of a Key/Value store.
`int`	`_max` Size of the serialized wad of bits.
`static byte`	`HDFS`
`static byte`	`ICE`
`static int`	`MAX`
`static byte`	`NFS`
`static byte`	`S3`
`static byte`	`TCP`

Constructor Summary

Constructors
Constructor and Description
`Value(Key k, Freezable pojo)` Standard constructor to build a Value from a POJO and a Key.
`Value(Key k, int max, byte[] mem, short type, byte be)` Construct a Value from all parts; not needed for most uses.

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`block()` Possibly blocks the current thread.
`java.lang.String`	`className()` Class name of the embedded POJO, without needing an actual POJO.
`void`	`freeMem()` Invalidate byte[] cache.
`void`	`freePOJO()` Invalidate POJO cache.
`<T extends Iced> T`	`get()` The FAST path get-POJO as an `Iced` subclass - final method for speed.
`<T extends Freezable> T`	`get(java.lang.Class<T> fc)` The FAST path get-POJO as a `Freezable` - final method for speed.
`<T extends Freezable> T`	`getFreezable()` The FAST path get-POJO as a `Freezable` - final method for speed.
`boolean`	`isFrame()` Check if the Value's POJO is a `Frame` subtype.
`boolean`	`isJob()` Check if the Value's POJO is a `Job` subtype.
`boolean`	`isKey()` Check if the Value's POJO is a `Key` subtype.
`boolean`	`isLockable()` Check if the Value's POJO is a `Lockable` subtype.
`boolean`	`isModel()` Check if the Value's POJO is a `Model` subtype.
`boolean`	`isPersisted()` Check if the backing byte[] has been saved-to-disk
`boolean`	`isReleasable()` Return true if blocking is unnecessary.
`static boolean`	`isSubclassOf(int type, java.lang.Class clz)` Check if the Value's POJO is a subtype of given type integer.
`boolean`	`isVec()` Check if the Value's POJO is a `Vec` subtype.
`boolean`	`isVecGroup()` Check if the Value's POJO is a `Vec.VectorGroup` subtype.
`byte[]`	`memOrLoad()` The FAST path get-byte-array - final method for speed.
`static java.lang.String`	`nameOfPersist(int x)` One of ICE, HDFS, S3, NFS or TCP, according to where this Value is persisted.
`Value`	`read_impl(AutoBuffer bb)` Implementation of the `Iced` serialization protocol, only called by auto-genned code.
`void`	`setdsk()` Used by the persistance subclass to mark this Value as saved-on-disk.
`java.lang.Class<? extends Freezable>`	`theFreezableClass()`
`int`	`type()`
`AutoBuffer`	`write_impl(AutoBuffer ab)` Implementation of the `Iced` serialization protocol, only called by auto-genned code.

Methods inherited from class water.Iced
clone, frozenType, read, readExternal, readJSON_impl, readJSON, toJsonString, write, writeExternal, writeHTML_impl, writeHTML, writeJSON_impl, writeJSON

Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - _key
```
public transient Key _key
```
    The Key part of a Key/Value store. Transient, because the Value is typically found via its Key, and so the Key is available before we get the Value and does not need to be passed around the wire. Not final, because Keys are interned slowly (for faster compares) and periodically a Value's Key will be updated to an interned but equivalent Key.
    Should not be set by any user code.
  - MAX
```
public static final int MAX
```
    See Also:
    Constant Field Values
  - _max
```
public int _max
```
    Size of the serialized wad of bits. Values are wads of bits; known small enough to 'chunk' politely on disk, or fit in a Java heap (larger Vecs are built via Chunks) but (much) larger than a UDP packet. Values can point to either the disk or ram version or both. There's no compression smarts (done by the big data Chunks) nor de-dup smarts (done by the nature of a K/V). This is just a local placeholder for some user bits being held at this local Node.
  - ICE
```
public static final byte ICE
```
    See Also:
    Constant Field Values
  - HDFS
```
public static final byte HDFS
```
    See Also:
    Constant Field Values
  - S3
```
public static final byte S3
```
    See Also:
    Constant Field Values
  - NFS
```
public static final byte NFS
```
    See Also:
    Constant Field Values
  - TCP
```
public static final byte TCP
```
    See Also:
    Constant Field Values
- Constructor Detail
  - Value
```
public Value(Key k,
     int max,
     byte[] mem,
     short type,
     byte be)
```
    Construct a Value from all parts; not needed for most uses. This special constructor is used by water.fvec to build Value objects over already-existing Files, so that the File contents will be lazily swapped-in as the Values are first used.
  - Value
```
public Value(Key k,
     Freezable pojo)
```
    Standard constructor to build a Value from a POJO and a Key.
- Method Detail
  - type
```
public int type()
```
  - className
```
public java.lang.String className()
```
    Class name of the embedded POJO, without needing an actual POJO.
  - freeMem
```
public final void freeMem()
```
    Invalidate byte[] cache. Only used to eagerly free memory, for data which is expected to be read-once.
  - freePOJO
```
public final void freePOJO()
```
    Invalidate POJO cache. Only used to eagerly free memory, for data which is expected to be read-once.
  - memOrLoad
```
public final byte[] memOrLoad()
```
    The FAST path get-byte-array - final method for speed. Will (re)build the mem array from either the POJO or disk. Never returns NULL.
    
    Returns:
    byte[] holding the serialized POJO
  - get
```
public final <T extends Iced> T get()
```
    The FAST path get-POJO as an Iced subclass - final method for speed. Will (re)build the POJO from the _mem array. Never returns NULL.
    
    Returns:
    The POJO, probably the cached instance.
  - get
```
public final <T extends Freezable> T get(java.lang.Class<T> fc)
```
    The FAST path get-POJO as a Freezable - final method for speed. Will (re)build the POJO from the _mem array. Never returns NULL. This version has more type-checking.
    
    Returns:
    The POJO, probably the cached instance.
  - getFreezable
```
public final <T extends Freezable> T getFreezable()
```
    The FAST path get-POJO as a Freezable - final method for speed. Will (re)build the POJO from the _mem array. Never returns NULL.
    
    Returns:
    The POJO, probably the cached instance.
  - setdsk
```
public final void setdsk()
```
    Used by the persistance subclass to mark this Value as saved-on-disk.
  - isPersisted
```
public final boolean isPersisted()
```
    Check if the backing byte[] has been saved-to-disk
  - nameOfPersist
```
public static java.lang.String nameOfPersist(int x)
```
    One of ICE, HDFS, S3, NFS or TCP, according to where this Value is persisted.
    
    Returns:
    Short String of the persitance name
  - isSubclassOf
```
public static boolean isSubclassOf(int type,
                   java.lang.Class clz)
```
    Check if the Value's POJO is a subtype of given type integer. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a subtype.
  - isKey
```
public boolean isKey()
```
    Check if the Value's POJO is a Key subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Key subtype.
  - isFrame
```
public boolean isFrame()
```
    Check if the Value's POJO is a Frame subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Frame subtype.
  - isVecGroup
```
public boolean isVecGroup()
```
    Check if the Value's POJO is a Vec.VectorGroup subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Vec.VectorGroup subtype.
  - isLockable
```
public boolean isLockable()
```
    Check if the Value's POJO is a Lockable subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Lockable subtype.
  - isVec
```
public boolean isVec()
```
    Check if the Value's POJO is a Vec subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Vec subtype.
  - isModel
```
public boolean isModel()
```
    Check if the Value's POJO is a Model subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Model subtype.
  - isJob
```
public boolean isJob()
```
    Check if the Value's POJO is a Job subtype. Does not require the POJO.
    
    Returns:
    True if the Value's POJO is a Job subtype.
  - theFreezableClass
```
public java.lang.Class<? extends Freezable> theFreezableClass()
```
  - write_impl
```
public AutoBuffer write_impl(AutoBuffer ab)
```
    Description copied from class: Iced
    
    Implementation of the Iced serialization protocol, only called by auto-genned code. Not intended to be called by user code. Override only for custom Iced serializers.
    
    Specified by:
    
    write_impl in interface Freezable
    
    Overrides:
    
    write_impl in class Iced
    
    Parameters:
    ab - AutoBuffer to write this object to.
    
    Returns:
    Returns the original AutoBuffer for flow-coding.
  - read_impl
```
public Value read_impl(AutoBuffer bb)
```
    Description copied from class: Iced
    
    Implementation of the Iced serialization protocol, only called by auto-genned code. Not intended to be called by user code. Override only for custom Iced serializers.
    
    Specified by:
    
    read_impl in interface Freezable
    
    Overrides:
    
    read_impl in class Iced
    
    Parameters:
    bb - AutoBuffer to read this object from.
    
    Returns:
    Returns a new instance of object reconstructed from AutoBuffer.
  - isReleasable
```
public boolean isReleasable()
```
    Return true if blocking is unnecessary. Alas, used in TWO places and the blocking API forces them to share here.
    
    Specified by:
    
    isReleasable in interface ForkJoinPool.ManagedBlocker
  - block
```
public boolean block()
```
    Possibly blocks the current thread. Returns true if isReleasable would return true. Used by the FJ Pool management to spawn threads to prevent deadlock is otherwise all threads would block on waits.
    
    Specified by:
    
    block in interface ForkJoinPool.ManagedBlocker
    
    Returns:
    true if no additional blocking is necessary (i.e., if isReleasable would return true)

Class Value

Field Summary

Constructor Summary

Method Summary

Methods inherited from class water.Iced

Methods inherited from class java.lang.Object

Field Detail

_key

MAX

_max

ICE

HDFS

S3

NFS

TCP

Constructor Detail

Value

Value

Method Detail

type

className

freeMem

freePOJO

memOrLoad

get

get

getFreezable

setdsk

isPersisted

nameOfPersist

isSubclassOf

isKey

isFrame

isVecGroup

isLockable

isVec

isModel

isJob

theFreezableClass

write_impl

read_impl

isReleasable

block