Bigtable使用Paxos算法来处理网络分区问题。当网络分区发生时,系统会自动进行一系列的失败转移操作,使得在网络分区后仍可以对数据进行写入和读取。在通过Paxos算法选举出新的主节点后,原主节点的数据将通过数据复制机制进行同步,以保证数据的一致性。下面给出使用Paxos算法实现的代码示例:
public class Paxos {
private final static int DEFAULT_PORT = 8888;
private final static int DEFAULT_RETRIES = 3;
private final static int DEFAULT_TIMEOUT = 2000;
enum ProposalType {
NORMAL, PREPARE, PROMISE, ACCEPT, ACCEPTED
}
class Proposal {
ProposalType type;
String value;
int ballotNumber;
int nodeID;
public Proposal(ProposalType type, String value, int ballotNumber, int nodeID) {
this.type = type;
this.value = value;
this.ballotNumber = ballotNumber;
this.nodeID = nodeID;
}
}
interface Network {
void send(int nodeID, String message);
String receive(int nodeID);
}
Network network;
int nodeID;
int quorumSize;
int retries = DEFAULT_RETRIES;
int timeout = DEFAULT_TIMEOUT;
int ballotNumber = 0;
String acceptedValue = null;
int acceptedBallotNumber = -1;
public Paxos(int nodeID, int quorumSize, Network network) {
this.nodeID = nodeID;
this.quorumSize = quorumSize;
this.network = network;
}
public void run() {
while (true) {
int latency = 0;
Proposal proposal = new Proposal(ProposalType.PREPARE, acceptedValue, ballotNumber + 1, nodeID);
int promiseCount = 0;
int maxBallot = -1;
List promises = new ArrayList();
for (int i = 0; i < quorumSize; i++) {
if (i == nodeID) {
continue;