快凌晨了，也到了工作10年的尾巴，技术专家这条路不好走。 回来研究一下CAP ZAB TCC XA等知识点，也是现在大公司面试主要问题点，解答思路其实很简单，是通过TCP协议保护（上层做协议封装）在高并发环境下的局域网内部，保证系统设计平衡性，即从事务方面下手，兼顾效率的同时也要保证高可用性。其中并未有高深的算法，更多的是逻辑上的若干层保护。
CommitProcessor类
queuedRequests和committedRequests 都是linkedList，保证顺序性；
public void processRequest(Request request) {
if (LOG.isDebugEnabled()) {
LOG.debug("Processing request:: " + request);
}
// request.addRQRec(">final");
long traceMask = ZooTrace.CLIENT_REQUEST_TRACE_MASK;
if (request.type == OpCode.ping) {
traceMask = ZooTrace.SERVER_PING_TRACE_MASK;
}
if (LOG.isTraceEnabled()) {
ZooTrace.logRequest(LOG, traceMask, 'E', request, "");
}
ProcessTxnResult rc = null;
synchronized (zks.outstandingChanges) {
//先处理服务器剩余
while (!zks.outstandingChanges.isEmpty()
&& zks.outstandingChanges.get(0).zxid <= request.zxid) {
ChangeRecord cr = zks.outstandingChanges.remove(0);
if (cr.zxid < request.zxid) {
LOG.warn("Zxid outstanding "
+ cr.zxid
+ " is less than current " + request.zxid);
}
if (zks.outstandingChangesForPath.get(cr.path) == cr) {
zks.outstandingChangesForPath.remove(cr.path);
}
}
if (request.hdr != null) {
TxnHeader hdr = request.hdr;
Record txn = request.txn;
//将请求头和记录处理并方到session
rc = zks.processTxn(hdr, txn);
}
// do not add non quorum packets to the queue.
//将操作动作类型的请求存放提交队列
if (Request.isQuorum(request.type)) {
zks.getZKDatabase().addCommittedProposal(request);
}
}
if (request.hdr != null && request.hdr.getType() == OpCode.closeSession) {
Factory scxn = zks.getServerCnxnFactory();
// this might be possible since
// we might just be playing diffs from the leader
if (scxn != null && request.cnxn == null) {
// calling this if we have the cnxn results in the client's
// close session response being lost - we've already closed
// the session/socket here before we can send the closeSession
// in the switch block below
scxn.closeSession(request.sessionId);
return;
}
}
if (request.cnxn == null) {
return;
}
ServerCnxn cnxn = request.cnxn;
String lastOp = "NA";
zks.decInProcess();
Code err = Code.OK;
Record rsp = null;
boolean closeSession = false;
try {
if (request.hdr != null && request.hdr.getType() == OpCode.error) {
throw KeeperException.create(KeeperException.Code.get((
(ErrorTxn) request.txn).getErr()));
}
KeeperException ke = request.getException();
if (ke != null) {
throw ke;
}
if (LOG.isDebugEnabled()) {
LOG.debug(request);
}
switch (request.type) {
case OpCode.ping: {
zks.serverStats().updateLatency(request.createTime);
lastOp = "PING";
((CnxnStats)cnxn.getStats())
.updateForResponse(request.cxid, request.zxid, lastOp,
request.createTime, System.currentTimeMillis());
cnxn.sendResponse(new ReplyHeader(-2,
zks.getZKDatabase().getDataTreeLastProcessedZxid(), 0), null, "response");
return;
}
case OpCode.createSession: {
zks.serverStats().updateLatency(request.createTime);
lastOp = "SESS";
((CnxnStats)cnxn.getStats())
.updateForResponse(request.cxid, request.zxid, lastOp,
request.createTime, System.currentTimeMillis());
cnxn.finishSessionInit(true);
return;
}
case OpCode.create: {
lastOp = "CREA";
rsp = new CreateResponse(rc.path);
err = Code.get(rc.err);
break;
}
case OpCode.delete: {
lastOp = "DELE";
err = Code.get(rc.err);
break;
}
case OpCode.setData: {
lastOp = "SETD";
rsp = new SetDataResponse(rc.stat);
err = Code.get(rc.err);
break;
}
case OpCode.setACL: {
lastOp = "SETA";
rsp = new SetACLResponse(rc.stat);
err = Code.get(rc.err);
break;
}
case OpCode.closeSession: {
lastOp = "CLOS";
closeSession = true;
err = Code.get(rc.err);
break;
}
case OpCode.sync: {
lastOp = "SYNC";
SyncRequest syncRequest = new SyncRequest();
ZooKeeperServer.byteBuffer2Record(request.request,
syncRequest);
rsp = new SyncResponse(syncRequest.getPath());
break;
}
case OpCode.exists: {
lastOp = "EXIS";
// TODO we need to figure out the security requirement for this!
ExistsRequest existsRequest = new ExistsRequest();
ZooKeeperServer.byteBuffer2Record(request.request,
existsRequest);
String path = existsRequest.getPath();
if (path.indexOf('\0') != -1) {
throw new KeeperException.BadArgumentsException();
}
Stat stat = zks.getZKDatabase().statNode(path, existsRequest
.getWatch() ? cnxn : null);
rsp = new ExistsResponse(stat);
break;
}
case OpCode.getData: {
lastOp = "GETD";
GetDataRequest getDataRequest = new GetDataRequest();
ZooKeeperServer.byteBuffer2Record(request.request,
getDataRequest);
DataNode n = zks.getZKDatabase().getNode(getDataRequest.getPath());
if (n == null) {
throw new KeeperException.NoNodeException();
}
Long aclL;
synchronized(n) {
aclL = n.acl;
}
PrepRequestProcessor.checkACL(zks, zks.getZKDatabase().convertLong(aclL),
ZooDefs.Perms.READ,
request.authInfo);
Stat stat = new Stat();
byte b[] = zks.getZKDatabase().getData(getDataRequest.getPath(), stat,
getDataRequest.getWatch() ? cnxn : null);
rsp = new GetDataResponse(b, stat);
break;
}
case OpCode.setWatches: {
lastOp = "SETW";
SetWatches setWatches = new SetWatches();
// XXX We really should NOT need this!!!!
request.request.rewind();
ZooKeeperServer.byteBuffer2Record(request.request, setWatches);
long relativeZxid = setWatches.getRelativeZxid();
zks.getZKDatabase().setWatches(relativeZxid,
setWatches.getDataWatches(),
setWatches.getExistWatches(),
setWatches.getChildWatches(), cnxn);
break;
}
case OpCode.getACL: {
lastOp = "GETA";
GetACLRequest getACLRequest = new GetACLRequest();
ZooKeeperServer.byteBuffer2Record(request.request,
getACLRequest);
Stat stat = new Stat();
List<ACL> acl =
zks.getZKDatabase().getACL(getACLRequest.getPath(), stat);
rsp = new GetACLResponse(acl, stat);
break;
}
case OpCode.getChildren: {
lastOp = "GETC";
GetChildrenRequest getChildrenRequest = new GetChildrenRequest();
ZooKeeperServer.byteBuffer2Record(request.request,
getChildrenRequest);
DataNode n = zks.getZKDatabase().getNode(getChildrenRequest.getPath());
if (n == null) {
throw new KeeperException.NoNodeException();
}
Long aclG;
synchronized(n) {
aclG = n.acl;
}
PrepRequestProcessor.checkACL(zks, zks.getZKDatabase().convertLong(aclG),
ZooDefs.Perms.READ,
request.authInfo);
List<String> children = zks.getZKDatabase().getChildren(
getChildrenRequest.getPath(), null, getChildrenRequest
.getWatch() ? cnxn : null);
rsp = new GetChildrenResponse(children);
break;
}
case OpCode.getChildren2: {
lastOp = "GETC";
GetChildren2Request getChildren2Request = new GetChildren2Request();
ZooKeeperServer.byteBuffer2Record(request.request,
getChildren2Request);
Stat stat = new Stat();
DataNode n = zks.getZKDatabase().getNode(getChildren2Request.getPath());
if (n == null) {
throw new KeeperException.NoNodeException();
}
Long aclG;
synchronized(n) {
aclG = n.acl;
}
PrepRequestProcessor.checkACL(zks, zks.getZKDatabase().convertLong(aclG),
ZooDefs.Perms.READ,
request.authInfo);
List<String> children = zks.getZKDatabase().getChildren(
getChildren2Request.getPath(), stat, getChildren2Request
.getWatch() ? cnxn : null);
rsp = new GetChildren2Response(children, stat);
break;
}
}
} catch (SessionMovedException e) {
// session moved is a connection level error, we need to tear
// down the connection otw ZOOKEEPER-710 might happen
// ie client on slow follower starts to renew session, fails
// before this completes, then tries the fast follower (leader)
// and is successful, however the initial renew is then
// successfully fwd/processed by the leader and as a result
// the client and leader disagree on where the client is most
// recently attached (and therefore invalid SESSION MOVED generated)
cnxn.sendCloseSession();
return;
} catch (KeeperException e) {
err = e.code();
} catch (Exception e) {
// log at error level as we are returning a marshalling
// error to the user
LOG.error("Failed to process " + request, e);
StringBuilder sb = new StringBuilder();
ByteBuffer bb = request.request;
bb.rewind();
while (bb.hasRemaining()) {
sb.append(Integer.toHexString(bb.get() & 0xff));
}
LOG.error("Dumping request buffer: 0x" + sb.toString());
err = Code.MARSHALLINGERROR;
}
long lastZxid = zks.getZKDatabase().getDataTreeLastProcessedZxid();
ReplyHeader hdr =
new ReplyHeader(request.cxid, lastZxid, err.intValue());
zks.serverStats().updateLatency(request.createTime);
((CnxnStats)cnxn.getStats())
.updateForResponse(request.cxid, lastZxid, lastOp,
request.createTime, System.currentTimeMillis());
//根据类型处理返回信息
try {
cnxn.sendResponse(hdr, rsp, "response");
if (closeSession) {
cnxn.sendCloseSession();
}
} catch (IOException e) {
LOG.error("FIXMSG",e);
}
}
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