Key (h2o-core 3.42.0 API)

java.lang.Object
- water.Iced<Key<T>>
- - water.Key<T>

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, java.lang.Cloneable, java.lang.Comparable, Freezable<Key<T>>
```
public final class Key<T extends Keyed>
extends Iced<Key<T>>
implements java.lang.Comparable
```
Keys! H2O supports a distributed Key/Value store, with exact Java Memory Model consistency. Keys are a means to find a Value somewhere in the Cloud, to cache it locally, to allow globally consistent updates to a Value. Keys have a *home*, a specific Node in the Cloud, which is computable from the Key itself. The Key's home node breaks ties on racing updates, and tracks caching copies (via a hardware-like MESI protocol), but otherwise is not involved in the DKV. All operations on the DKV, including Gets and Puts, are found in DKV.
Keys are defined as a simple byte-array, plus a hashCode and a small cache of Cloud-specific information. The first byte of the byte-array determines if this is a user-visible Key or an internal system Key; an initial byte of <32 is a system Key. User keys are generally externally visible, system keys are generally limited to things kept internal to the H2O Cloud. Keys might be a high-count item, hence we care about the size.
System keys for Job, Vec, Chunk and Vec.VectorGroup have special initial bytes; Keys for these classes can be determined without loading the underlying Value. Layout for Vec and Chunk is further restricted, so there is an efficient mapping between a numbered Chunk and it's associated Vec.
System keys (other than the restricted Vec and Chunk keys) can have their home node forced, by setting the desired home node in the first few Key bytes. Otherwise home nodes are selected by pseudo-random hash. Selecting a home node is sometimes useful for Keys with very high update rates coming from a specific Node.

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`byte[]`	`_kb`
`static byte`	`CHK`
`static byte`	`GRP`
`static byte`	`HIDDEN_USER_KEY`
`static byte`	`JOB`
`static byte`	`USER_KEY`
`static byte`	`VEC`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods
Modifier and Type	Method and Description
`int`	`compareTo(java.lang.Object o)` Lexically ordered Key comparison, so Keys can be sorted.
`boolean`	`equals(java.lang.Object o)`
`T`	`get()` Convenience function to fetch key contents from the DKV.
`Key`	`getVecKey()` Returns the `Vec` Key from a `Chunk` Key.
`int`	`hashCode()`
`H2ONode`	`home_node()` The home node for this Key.
`boolean`	`home()` True if the `home_node()` is the current node.
`boolean`	`isChunkKey()` True is this is a `Chunk` Key.
`boolean`	`isVec()` True is this is a `Vec` Key.
`static <P extends Keyed> Key<P>`	`make()`
`static <P extends Keyed> Key<P>`	`make(byte[] kb)`
`static <P extends Keyed> Key<P>`	`make(byte systemType, boolean required, H2ONode home)` Factory making a homed system Key.
`static <P extends Keyed> Key<P>`	`make(H2ONode node)` Make a random key, homed to a given node.
`static <P extends Keyed> Key<P>`	`make(java.lang.String s)` Factory making a Key from a String
`static <P extends Keyed> Key<P>`	`make(java.lang.String s, byte systemType)` Factory making a system Key.
`static <P extends Keyed> Key<P>`	`make(java.lang.String s, byte systemType, boolean required, H2ONode home)` Factory making a homed system Key.
`static <P extends Keyed> Key<P>`	`makeSystem(java.lang.String s)`
`static <P extends Keyed> Key<P>`	`makeUserHidden(java.lang.String s)`
`static java.lang.String`	`rand()` A random string, useful as a Key name or partial Key suffix.
`static Key`	`read_impl(Key k, AutoBuffer ab)`
`void`	`remove()` Deprecated. use `Keyed.remove(Key)` instead. Will be removed from version 3.30.
`Futures`	`remove(Futures fs)` Deprecated. use `Keyed.remove(Futures)` instead. Will be removed from version 3.30.
`java.lang.String`	`toString()` Converts the key to HTML displayable string.
`int`	`type()` System type/byte of a Key, or the constant `USER_KEY`
`boolean`	`user_allowed()` True if a `USER_KEY` and not a system key.
`java.lang.String`	`valueClass()` Return the classname for the Value that this Key points to, if any (e.g., "water.fvec.Frame").
`java.lang.String`	`valueClassSimple()` Return the base classname (not including the package) for the Value that this Key points to, if any (e.g., "Frame").
`static AutoBuffer`	`write_impl(Key k, AutoBuffer ab)`
`static AutoBuffer`	`writeJSON_impl(Key k, AutoBuffer ab)`

Methods inherited from class water.Iced
asBytes, clone, copyOver, frozenType, read, readExternal, readJSON, reloadFromBytes, toJsonBytes, toJsonString, write, writeExternal, writeJSON

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

- Field Detail
 - _kb
```
public final byte[] _kb
```
 - JOB
```
public static final byte JOB
```
 See Also:
 
 Constant Field Values
 - VEC
```
public static final byte VEC
```
 See Also:
 
 Constant Field Values
 - CHK
```
public static final byte CHK
```
 See Also:
 
 Constant Field Values
 - GRP
```
public static final byte GRP
```
 See Also:
 
 Constant Field Values
 - HIDDEN_USER_KEY
```
public static final byte HIDDEN_USER_KEY
```
 See Also:
 
 Constant Field Values
 - USER_KEY
```
public static final byte USER_KEY
```
 See Also:
 
 Constant Field Values
- Method Detail
 - isVec
```
public final boolean isVec()
```
 True is this is a Vec Key.
 
 Returns:
 
 True is this is a Vec Key
 - isChunkKey
```
public final boolean isChunkKey()
```
 True is this is a Chunk Key.
 
 Returns:
 
 True is this is a Chunk Key
 - getVecKey
```
public final Key getVecKey()
```
 Returns the Vec Key from a Chunk Key.
 
 Returns:
 
 Returns the Vec Key from a Chunk Key.
 - get
```
public final T get()
```
 Convenience function to fetch key contents from the DKV.
 
 Returns:
 
 null if the Key is not mapped, or an instance of Keyed
 - home
```
public boolean home()
```
 True if the home_node() is the current node.
 
 Returns:
 
 True if the home_node() is the current node
 - home_node
```
public H2ONode home_node()
```
 The home node for this Key.
 
 Returns:
 
 The home node for this Key.
 - make
```
public static  Key make(byte[] kb)
```
 - rand
```
public static java.lang.String rand()
```
 A random string, useful as a Key name or partial Key suffix.
 
 Returns:
 
 A random short string
 - make
```
public static  Key make(java.lang.String s)
```
 Factory making a Key from a String
 
 Returns:
 
 Desired Key
 - makeSystem
```
public static  Key makeSystem(java.lang.String s)
```
 - makeUserHidden
```
public static  Key makeUserHidden(java.lang.String s)
```
 - make
```
public static  Key make(H2ONode node)
```
 Make a random key, homed to a given node.
 
 Parameters:
 
 node - a node at which the new key is homed.
 
 Returns:
 
 the new key
 - make
```
public static  Key make()
```
 - make
```
public static  Key make(java.lang.String s,
 byte systemType,
 boolean required,
 H2ONode home)
```
 Factory making a homed system Key. Requires the initial system byte but then allows a String for the remaining bytes. Requires specifying the home node of the key. The required specifies if it is an error to name an H2ONode that is NOT in the Cloud, or if some other H2ONode can be substituted.
 
 Returns:
 
 the desired Key
 - make
```
public static  Key make(java.lang.String s,
 byte systemType)
```
 Factory making a system Key. Requires the initial system byte but then allows a String for the remaining bytes.
 
 Returns:
 
 the desired Key
 - make
```
public static  Key make(byte systemType,
 boolean required,
 H2ONode home)
```
 Factory making a homed system Key. Requires the initial system byte and uses rand() for the remaining bytes. Requires specifying the home node of the key. The required specifies if it is an error to name an H2ONode that is NOT in the Cloud, or if some other H2ONode can be substituted.
 
 Returns:
 
 the desired Key
 - remove
```
public void remove()
```
 Deprecated. use Keyed.remove(Key) instead. Will be removed from version 3.30.
 
 Remove a Key from the DKV, including any embedded Keys.
 - remove
```
public Futures remove(Futures fs)
```
 Deprecated. use Keyed.remove(Futures) instead. Will be removed from version 3.30.
 - user_allowed
```
public boolean user_allowed()
```
 True if a USER_KEY and not a system key.
 
 Returns:
 
 True if a USER_KEY and not a system key
 - type
```
public int type()
```
 System type/byte of a Key, or the constant USER_KEY
 
 Returns:
 
 Key type
 - valueClass
```
public java.lang.String valueClass()
```
 Return the classname for the Value that this Key points to, if any (e.g., "water.fvec.Frame").
 - valueClassSimple
```
public java.lang.String valueClassSimple()
```
 Return the base classname (not including the package) for the Value that this Key points to, if any (e.g., "Frame").
 - toString
```
public java.lang.String toString()
```
 Converts the key to HTML displayable string. For user keys returns the key itself, for system keys returns their hexadecimal values.
 
 Overrides:
 
 toString in class java.lang.Object
 
 Returns:
 
 key as a printable string
 - hashCode
```
public int hashCode()
```
 Overrides:
 
 hashCode in class java.lang.Object
 - equals
```
public boolean equals(java.lang.Object o)
```
 Overrides:
 
 equals in class java.lang.Object
 - compareTo
```
public int compareTo(java.lang.Object o)
```
 Lexically ordered Key comparison, so Keys can be sorted. Modestly expensive.
 
 Specified by:
 
 compareTo in interface java.lang.Comparable
 - write_impl
```
public static final AutoBuffer write_impl(Key k,
 AutoBuffer ab)
```
 - read_impl
```
public static final Key read_impl(Key k,
 AutoBuffer ab)
```
 - writeJSON_impl
```
public static final AutoBuffer writeJSON_impl(Key k,
 AutoBuffer ab)
```

Class Key<T extends Keyed>

Field Summary

Method Summary

Methods inherited from class water.Iced

Methods inherited from class java.lang.Object

Field Detail

_kb

JOB

VEC

CHK

GRP

HIDDEN_USER_KEY

USER_KEY

Method Detail

isVec

isChunkKey

getVecKey

get

home

home_node

make

rand

make

makeSystem

makeUserHidden

make

make

make

make

make

remove

remove

user_allowed

type

valueClass

valueClassSimple

toString

hashCode

equals

compareTo

write_impl

read_impl

writeJSON_impl