Replica (starrocks-bdb-je 18.3.17 API)

java.lang.Object
- com.sleepycat.je.rep.impl.node.Replica

```
public class Replica
extends Object
```
The Replica class is the locus of the replay operations and replica transaction consistency tracking and management operations at a replica node. A single instance of this class is created when the replication node is created and exists for the lifetime of the replication node, although it is only really used when the node is operating as a Replica. Note that the Replica (like the FeederManager) does not have its own independent thread of control; it runs in the RepNode's thread. To make the network I/O as aync as possible, and avoid stalls during network I/O the input and output are done in separate threads. The overall thread and queue organization is as sketched below: read from network -> RepNodeThread (does read) -> replayQueue replayQueue -> ReplayThread -> outputQueue outputQueue -> ReplicaOutputThread (does write) -> writes to network This three thread organization has the following benefits over a single thread replay model: 1) It makes the heartbeat mechanism used to determine whether the HA sockets are in use more reliable. This is because a heartbeat response cannot be blocked by lock contention in the replay thread, since a heartbeat can be sent spontaneously (without an explicit heartbeat request from the feeder) by the ReplicaOutputThread, if a heartbeat had not been sent during a heartbeat interval period. 2) The cpu load in the replay thread is reduced by offloading the network-specific aspects of the processing to different threads. It's important to keep the CPU load in this thread at a minimum so we can use a simple single thread replay scheme. 3) Prevents replay thread stalls by input and output buffering in the two threads on either side of it. With jdk 1.7 we could eliminate the use of these threads and switch over to the new aysnc I/O APIs, but that involves a lot more code restructuring.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`class`	`Replica.ConsistencyTracker` Tracks the consistency of this replica wrt the Master.
`static class`	`Replica.HardRecoveryElectionException` Indicates that an election is needed before the hard recovery can proceed.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`protected void`	`doRunReplicaLoopInternalWork()`
`Replica.ConsistencyTracker`	`getConsistencyTracker()`
`DbCache`	`getDbCache()`
`long`	`getMasterTxnEndVLSN()` Returns the last commit VLSN at the master, as known at the replica.
`StatGroup`	`getProtocolStats(StatsConfig config)`
`StatGroup`	`getReplayStats(StatsConfig config)` Returns the replay statistics associated with the Replica.
`ReplicaFeederSyncup.TestHook<Object>`	`getReplicaFeederSyncupHook()`
`ReplicaOutputThread`	`getReplicaOutputThread()` For test use only.
`int`	`getTestDelayMs()`
`StatGroup`	`getTrackerStats(StatsConfig config)`
`VLSN`	`getTxnEndVLSN()`
`Replay`	`replay()`
`void`	`resetStats()`
`void`	`setDontProcessStream()` For unit testing only!
`static void`	`setInitialReplayHook(TestHook<BinaryProtocol.Message> hook)` Sets a test hook for installation into Replica class instances to be created in the future.
`void`	`setReplicaFeederSyncupHook(ReplicaFeederSyncup.TestHook<Object> syncupHook)` Set a test hook which is executed when the ReplicaFeederSyncup finishes.
`void`	`setTestDelayMs(int testDelayMs)` For unit testing only!
`void`	`shutdown()` Shutdown the Replica, free any threads that may have been waiting for the replica to reach some degree of consistency.

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

- Method Detail
  - shutdown
```
public void shutdown()
```
    Shutdown the Replica, free any threads that may have been waiting for the replica to reach some degree of consistency. This method is only invoked as part of the repnode shutdown. If the shutdown is being executed from a different thread, it attempts to interrupt the thread by first shutting down the channel it may be waiting on for input from the feeder. The replica thread should notice the channel shutdown and/or the shutdown state of the rep node itself. The caller will use harsher methods, like an interrupt, if the rep node thread (Replica or Feeder) is still active.
  - setTestDelayMs
```
public void setTestDelayMs(int testDelayMs)
```
    For unit testing only!
  - getTestDelayMs
```
public int getTestDelayMs()
```
  - setDontProcessStream
```
public void setDontProcessStream()
```
    For unit testing only!
  - getTxnEndVLSN
```
public VLSN getTxnEndVLSN()
```
  - replay
```
public Replay replay()
```
  - getDbCache
```
public DbCache getDbCache()
```
  - getConsistencyTracker
```
public Replica.ConsistencyTracker getConsistencyTracker()
```
  - getMasterTxnEndVLSN
```
public long getMasterTxnEndVLSN()
```
    Returns the last commit VLSN at the master, as known at the replica.
    
    Returns:
    
    the commit VLSN
  - getReplicaOutputThread
```
public ReplicaOutputThread getReplicaOutputThread()
```
    For test use only.
  - doRunReplicaLoopInternalWork
```
protected void doRunReplicaLoopInternalWork()
                                     throws Exception
```
    Throws:
    
    Exception
  - getReplayStats
```
public StatGroup getReplayStats(StatsConfig config)
```
    Returns the replay statistics associated with the Replica.
    
    Returns:
    
    the statistics.
  - getProtocolStats
```
public StatGroup getProtocolStats(StatsConfig config)
```
  - getTrackerStats
```
public StatGroup getTrackerStats(StatsConfig config)
```
  - resetStats
```
public void resetStats()
```
  - setInitialReplayHook
```
public static void setInitialReplayHook(TestHook<BinaryProtocol.Message> hook)
```
    Sets a test hook for installation into Replica class instances to be created in the future. This is needed when the test hook must be installed before the ReplicatedEnvironment handle constructor returns, so that a test may influence the replay of the sync-up transaction backlog.
  - setReplicaFeederSyncupHook
```
public void setReplicaFeederSyncupHook(ReplicaFeederSyncup.TestHook<Object> syncupHook)
```
    Set a test hook which is executed when the ReplicaFeederSyncup finishes. This differs from the static method ReplicaFeederSyncup.setGlobalSyncupHook in that it sets the hook for a specific node, whereas the other method is static and sets it globally. This method is required when a test is trying to set the hook for only one node, and the node already exists. The other method is useful when a test is trying to set the hook before a node exists.
  - getReplicaFeederSyncupHook
```
public ReplicaFeederSyncup.TestHook<Object> getReplicaFeederSyncupHook()
```

Class Replica

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Method Detail

shutdown

setTestDelayMs

getTestDelayMs

setDontProcessStream

getTxnEndVLSN

replay

getDbCache

getConsistencyTracker

getMasterTxnEndVLSN

getReplicaOutputThread

doRunReplicaLoopInternalWork

getReplayStats

getProtocolStats

getTrackerStats

resetStats

setInitialReplayHook

setReplicaFeederSyncupHook

getReplicaFeederSyncupHook