FallbackTarget (Permazen 4.1.8 API)

java.lang.Object
- io.permazen.kv.raft.fallback.FallbackTarget

All Implemented Interfaces:

Cloneable
```
public class FallbackTarget
extends Object
implements Cloneable
```
Represents one of the underlying RaftKVDatabases managed by a FallbackKVDatabase.
Instances must at least be configured with the associated RaftKVDatabase; all other properties have defaults. Two MergeStrategys are configured to handle switching into (see setUnavailableMergeStrategy()) and out of (see setRejoinMergeStrategy()) standalone mode.
Other parameters configure how cluster availability is determined and enforce hysteresis; see setTransactionTimeout(), setCheckInterval(), setMinAvailableTime(), and setMinUnavailableTime().

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`DEFAULT_CHECK_INTERVAL` Default check interval (2000ms).
`static int`	`DEFAULT_MIN_AVAILABLE_TIME` Default minimum available type (10000ms).
`static int`	`DEFAULT_MIN_UNAVAILABLE_TIME` Default minimum unavailable type (30000ms).
`static int`	`DEFAULT_TRANSACTION_TIMEOUT` Default transaction timeout for assessing availability (1000ms).
`protected Logger`	`log`

Constructor Summary

Constructors
Constructor and Description

FallbackTarget()

Constructors
Constructor and Description
`FallbackTarget()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`protected boolean`	`checkAvailability(FallbackKVDatabase fallbackDB)` Perform an availability assessment of the underlying `RaftKVDatabase` associated with this instance.
`FallbackTarget`	`clone()`
`int`	`getCheckInterval()` Get the interval between availability checks.
`Date`	`getLastActiveTime()` Get the last time this target was the active database.
`Date`	`getLastChangeTime()` Get the time of the last change in availability of this target, if known.
`int`	`getMinAvailableTime()` Get the minimum amount of time after becoming available before allowing this instance to become unavailable again.
`int`	`getMinUnavailableTime()` Get the minimum amount of time after becoming unavailable before allowing this instance to become available again.
`RaftKVDatabase`	`getRaftKVDatabase()` Get the `RaftKVDatabase`.
`MergeStrategy`	`getRejoinMergeStrategy()` Get the merge strategy to apply when transitioning from a lower priority database to this database because our `RaftKVDatabase` cluster has become available.
`int`	`getTransactionTimeout()` Get the transaction timeout used when determining database availability.
`MergeStrategy`	`getUnavailableMergeStrategy()` Get the merge strategy to apply when transitioning from this database to a lower priority database because our `RaftKVDatabase` cluster has become unavailable.
`boolean`	`isAvailable()` Get the current availability of this target.
`void`	`setCheckInterval(int checkInterval)` Configure the interval between availability checks.
`void`	`setMinAvailableTime(int minAvailableTime)` Configure the minimum amount of time after becoming available before allowing this instance to become unavailable again.
`void`	`setMinUnavailableTime(int minUnavailableTime)` Configure the minimum amount of time after becoming unavailable before allowing this instance to become available again.
`void`	`setRaftKVDatabase(RaftKVDatabase raft)` Set the `RaftKVDatabase`.
`void`	`setRejoinMergeStrategy(MergeStrategy strategy)` Configure the merge strategy to apply when transitioning from a lower priority database to this database because our `RaftKVDatabase` cluster has become available again.
`void`	`setTransactionTimeout(int timeout)` Configure the transaction timeout used when determining database availability.
`void`	`setUnavailableMergeStrategy(MergeStrategy strategy)` Configure the merge strategy to apply when transitioning from this database to a lower priority database because our `RaftKVDatabase` cluster has become unavailable.
`String`	`toString()`

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

- Field Detail
  - DEFAULT_TRANSACTION_TIMEOUT
```
public static final int DEFAULT_TRANSACTION_TIMEOUT
```
    Default transaction timeout for assessing availability (1000ms).
    
    See Also:
    
    setTransactionTimeout(), Constant Field Values
  - DEFAULT_CHECK_INTERVAL
```
public static final int DEFAULT_CHECK_INTERVAL
```
    Default check interval (2000ms).
    
    See Also:
    
    setCheckInterval(), Constant Field Values
  - DEFAULT_MIN_AVAILABLE_TIME
```
public static final int DEFAULT_MIN_AVAILABLE_TIME
```
    Default minimum available type (10000ms).
    
    See Also:
    
    setMinAvailableTime(), Constant Field Values
  - DEFAULT_MIN_UNAVAILABLE_TIME
```
public static final int DEFAULT_MIN_UNAVAILABLE_TIME
```
    Default minimum unavailable type (30000ms).
    
    See Also:
    
    setMinUnavailableTime(), Constant Field Values
  - log
```
protected final Logger log
```
- Constructor Detail
  - FallbackTarget
```
public FallbackTarget()
```
- Method Detail
  - getRaftKVDatabase
```
public RaftKVDatabase getRaftKVDatabase()
```
    Get the RaftKVDatabase.
    
    Returns:
    
    underlying database
  - setRaftKVDatabase
```
public void setRaftKVDatabase(RaftKVDatabase raft)
```
    Set the RaftKVDatabase.
    
    Parameters:
    
    raft - underlying database
  - getTransactionTimeout
```
public int getTransactionTimeout()
```
    Get the transaction timeout used when determining database availability.
    
    Returns:
    
    transaction timeout in milliseconds
  - setTransactionTimeout
```
public void setTransactionTimeout(int timeout)
```
    Configure the transaction timeout used when determining database availability.
    Default is DEFAULT_TRANSACTION_TIMEOUT.
    
    Parameters:
    
    timeout - timeout in milliseconds
    
    Throws:
    
    IllegalArgumentException - if timeout is not greater than zero
  - getCheckInterval
```
public int getCheckInterval()
```
    Get the interval between availability checks.
    
    Returns:
    
    check interval in milliseconds
  - setCheckInterval
```
public void setCheckInterval(int checkInterval)
```
    Configure the interval between availability checks.
    Default is DEFAULT_CHECK_INTERVAL.
    
    Parameters:
    
    checkInterval - check interval in milliseconds
    
    Throws:
    
    IllegalArgumentException - if checkInterval is not greater than zero
  - getMinAvailableTime
```
public int getMinAvailableTime()
```
    Get the minimum amount of time after becoming available before allowing this instance to become unavailable again.
    
    Returns:
    
    minimum available time in milliseconds
  - setMinAvailableTime
```
public void setMinAvailableTime(int minAvailableTime)
```
    Configure the minimum amount of time after becoming available before allowing this instance to become unavailable again.
    Default is DEFAULT_MIN_AVAILABLE_TIME.
    
    Parameters:
    
    minAvailableTime - minimum available time in milliseconds
    
    Throws:
    
    IllegalArgumentException - if minAvailableTime is not greater than zero
  - getMinUnavailableTime
```
public int getMinUnavailableTime()
```
    Get the minimum amount of time after becoming unavailable before allowing this instance to become available again.
    
    Returns:
    
    minimum unavailable time in milliseconds
  - setMinUnavailableTime
```
public void setMinUnavailableTime(int minUnavailableTime)
```
    Configure the minimum amount of time after becoming unavailable before allowing this instance to become available again.
    Default is DEFAULT_MIN_UNAVAILABLE_TIME.
    
    Parameters:
    
    minUnavailableTime - minimum unavailable time in milliseconds
    
    Throws:
    
    IllegalArgumentException - if minUnavailableTime is not greater than zero
  - getUnavailableMergeStrategy
```
public MergeStrategy getUnavailableMergeStrategy()
```
    Get the merge strategy to apply when transitioning from this database to a lower priority database because our RaftKVDatabase cluster has become unavailable.
    
    Returns:
    
    unavailable merge strategy
  - setUnavailableMergeStrategy
```
public void setUnavailableMergeStrategy(MergeStrategy strategy)
```
    Configure the merge strategy to apply when transitioning from this database to a lower priority database because our RaftKVDatabase cluster has become unavailable.
    Default is OverwriteMergeStrategy.
    
    Parameters:
    
    strategy - unavailable merge strategy
    
    Throws:
    
    IllegalArgumentException - if strategy is null
  - getRejoinMergeStrategy
```
public MergeStrategy getRejoinMergeStrategy()
```
    Get the merge strategy to apply when transitioning from a lower priority database to this database because our RaftKVDatabase cluster has become available.
    
    Returns:
    
    rejoin merge strategy
  - setRejoinMergeStrategy
```
public void setRejoinMergeStrategy(MergeStrategy strategy)
```
    Configure the merge strategy to apply when transitioning from a lower priority database to this database because our RaftKVDatabase cluster has become available again.
    Default is NullMergeStrategy.
    
    Parameters:
    
    strategy - rejoin merge strategy
    
    Throws:
    
    IllegalArgumentException - if strategy is null
  - isAvailable
```
public boolean isAvailable()
```
    Get the current availability of this target.
    
    Returns:
    
    true if this target is currently available, otherwise false
  - getLastChangeTime
```
public Date getLastChangeTime()
```
    Get the time of the last change in availability of this target, if known.
    
    Returns:
    
    time this target's availability last changed, or null if unknown or no change has occurred
  - getLastActiveTime
```
public Date getLastActiveTime()
```
    Get the last time this target was the active database.
    
    Returns:
    
    last active time of this target, or null if never active
  - checkAvailability
```
protected boolean checkAvailability(FallbackKVDatabase fallbackDB)
```
    Perform an availability assessment of the underlying RaftKVDatabase associated with this instance.
    This method may block for as long as necessary to determine availability, but it should not block indefinitely. If a KVTransaction is opened, setTimeout() should be used to set a time limit.
    This method will not be invoked concurrently by two different threads.
    If this method throws an unchecked exception, the database will be assumed to be unavailable.
    The implementation in FallbackTarget determines availability by attempting to commit a read-only, Consistency.LINEARIZABLE transaction within the configured maximum timeout.
    
    Parameters:
    
    fallbackDB - parent fallback database
    
    Returns:
    
    true if database is available, false otherwise
  - clone
```
public FallbackTarget clone()
```
    Overrides:
    
    clone in class Object
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object

Class FallbackTarget

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

DEFAULT_TRANSACTION_TIMEOUT

DEFAULT_CHECK_INTERVAL

DEFAULT_MIN_AVAILABLE_TIME

DEFAULT_MIN_UNAVAILABLE_TIME

log

Constructor Detail

FallbackTarget

Method Detail

getRaftKVDatabase

setRaftKVDatabase

getTransactionTimeout

setTransactionTimeout

getCheckInterval

setCheckInterval

getMinAvailableTime

setMinAvailableTime

getMinUnavailableTime

setMinUnavailableTime

getUnavailableMergeStrategy

setUnavailableMergeStrategy

getRejoinMergeStrategy

setRejoinMergeStrategy

isAvailable

getLastChangeTime

getLastActiveTime

checkAvailability

clone

toString