redis原始碼分析之十叢集之二GossIP
阿新 • • 發佈：2020-12-29
一、P2P通訊
傳統的網際網路設計，包括現在主流的網際網路系統，基本是中心化的，也就是說，一切的網上活動，都需要經過一個服務中心（這是一個邏輯表述，不要和一個點，一個機器，一個機房等混淆），使用者所有的動作，從理論上講，都可以被服務端記錄和控制。它和現實社會是對應的，比如去火車站買票，必須去火車站（雖然說現在不用親自去火車站，但中心化反而更嚴重了）。買東西，必須去超市和菜市場，就是要打個電話，也得去電信公司辦個卡。而這些，都是中心化的，只不過可能使用者在辦理的時候兒感覺不到這個中心的存在。
而P2P是什麼呢？Peer to Peer，點到點的意思。就是說，使用者和使用者直接通訊，不過服務中心。可有的人說了，不過中心，怎麼找到其它人呢？你比如打電話，不在電信局註冊買個卡，別人怎麼知道？是啊。確實是這樣，可是，這難不倒有心人。舉個例子，比如大家常聽說的小道訊息，為啥小道訊息流傳那麼快？可能源頭只是王大麻子和趙二老婆說了句，聽說老李家兒子中了一千萬的彩票，結果一個小時不到，全村子人都知道了。P2P也可以模擬這種方法，是不是照樣沒有一箇中心服務也可以達到訊息傳播的目的。
1、傳統的中心拓撲
中心拓撲，是指由N個指定的中心結點，做為網路節點發現的提供節點，每個Peer登陸後，先去中心化節點要相關通訊節點資料。它的缺點和傳統的中心化服務基本類似，容易形成單點，容易有法律風險等。Napster是一個比較典型的例子。
2、完全去中心化的拓撲
通過使用洪泛演算法或者隨機演算法來，利用TTL減值實現，它沒有中心檢索伺服器，各個結點完全是對等的。但是它的缺點也很明顯，就是網路無法支援過大，否則會造成網路流量劇增，無法準確發現和快速擴充套件。它的主要代表是Gnutella這個檔案共享系統。
3、全分佈布式的結構化拓撲
DHT，完全分散式結構化拓撲網路，通過一個巨大散列表，實現節點對映來實現網路的管理。實現快速發速和擴充套件。它典型的案例是apestry，Chord,CAN,和Pastry。
也叫做Hybrid Structure，混合型組織結構。其實在看到上面的分列各種情況式，就會自然想到可不可以把它們結合起來。既可以吸取中心化的優勢，又可以有分散式的優勢，那就可以選擇一些節點做為超級節點（SuperNodes），做為中心節點負責節點資訊的轉發和儲存。
而在實際的應用過程中，發現和傳播網路資訊的演算法非常重要，常用的演算法主要有：
1、洪泛演算法
2、Gossip流言演算法
3、KAD演算法
因為洪泛演算法有可能引起網路風暴，所以一般現在主流的P2P中都採用了後兩者。而在Redis中也是使用的GossIP協議。
二、GossIP
GossIP又叫epidemic 協議（epidemic protocol），也就是流言演算法，也被稱為反熵（Anti-Entropy）演算法，就如前面的例子中說到的八卦協議，小道訊息。它是基於流行病的傳播方式的節點或者程序間資訊交換的協議。GossIP的特點在於它並不把網路資料發給所有的鄰居節點，而隨機選取N個（一般是8個以內）傳播。這就大大減少了相關的網路資料傳送的壓力，即使網路擴充套件到非常大，通訊壓力的增加也幾乎可以忽略。
typedef struct {
char nodename[CLUSTER_NAMELEN];
uint32_t ping_sent;
uint32_t pong_received;
char ip[NET_IP_STR_LEN]; /* IP address last time it was seen */
uint16_t port; /* base port last time it was seen */
uint16_t cport; /* cluster port last time it was seen */
uint16_t flags; /* node->flags copy */
uint32_t notused1;
} clusterMsgDataGossip;
typedef struct {
char nodename[CLUSTER_NAMELEN];
} clusterMsgDataFail;
typedef struct {
uint32_t channel_len;
uint32_t message_len;
unsigned char bulk_data[8]; /* 8 bytes just as placeholder. */
} clusterMsgDataPublish;
typedef struct {
uint64_t configEpoch; /* Config epoch of the specified instance. */
char nodename[CLUSTER_NAMELEN]; /* Name of the slots owner. */
unsigned char slots[CLUSTER_SLOTS/8]; /* Slots bitmap. */
} clusterMsgDataUpdate;
typedef struct {
uint64_t module_id; /* ID of the sender module. */
uint32_t len; /* ID of the sender module. */
uint8_t type; /* Type from 0 to 255. */
unsigned char bulk_data[3]; /* 3 bytes just as placeholder. */
} clusterMsgModule;
union clusterMsgData {
/* PING, MEET and PONG */
struct {
/* Array of N clusterMsgDataGossip structures */
clusterMsgDataGossip gossip[1];
} ping;
/* FAIL */
struct {
clusterMsgDataFail about;
} fail;
/* PUBLISH */
struct {
clusterMsgDataPublish msg;
} publish;
/* UPDATE */
struct {
clusterMsgDataUpdate nodecfg;
} update;
/* MODULE */
struct {
clusterMsgModule msg;
} module;
}
typedef struct {
char sig[4]; /* Signature "RCmb" (Redis Cluster message bus).訊號標識 * /
uint32_t totlen; /* Total length of this message */
uint16_t ver; /* Protocol version, currently set to 1. * /
uint16_t port; /* TCP base port number. */
uint16_t type; /* Message type訊息型別，比如meet,ping,pong,fail * /
uint16_t count; /* Only used for some kind of messages. */
uint64_t currentEpoch; /* The epoch accordingly to the sending node. 傳送節點的配置紀元*/
uint64_t configEpoch; /* The config epoch if it's a master, or the last
epoch advertised by its master if it is a
slave. 主副中主節點的配置紀元*/
uint64_t offset; /* Master replication offset if node is a master or
processed replication offset if node is a slave. */
char sender[CLUSTER_NAMELEN]; /* Name of the sender node */
unsigned char myslots[CLUSTER_SLOTS/8];//佔用空間最大的部分，槽資訊
char slaveof[CLUSTER_NAMELEN];
char myip[NET_IP_STR_LEN]; /* Sender IP, if not all zeroed. */
char notused1[34]; /* 34 bytes reserved for future usage. */
uint16_t cport; /* Sender TCP cluster bus port */
uint16_t flags; /* Sender node flags */
unsigned char state; /* Cluster state from the POV of the sender * /
unsigned char mflags[3]; /* Message flags: CLUSTERMSG_FLAG[012]_ ... * /
union clusterMsgData data;
} clusterMsg;
這個訊息結構體，佔用空間最大的是說明的那個陣列，大約是16384÷8÷1024=2kb，另外還會攜帶至少3個節點的資訊（一般為叢集總節點的十分之一），10個節點的狀態資訊約為1KB。通過這些資料的計算，加上每秒掃描10次，約定是大於接受PONG時間cluster-node-timeout/2 進行心跳，消耗的頻寬約為：N(一次心跳單元資料量)* NUM（心跳數量）。
其中，N上面有簡單計算，它會隨著叢集數量增加同時增加。NUM為心跳數量，也會隨著叢集增大而增大，如果叢集有200節點，分別部署在20*10（20臺物理機，每機10節點）的環境上，使用心跳預設的15秒，消耗頻寬約為25M。
int clusterProcessPacket(clusterLink *link) {
clusterMsg *hdr = (clusterMsg*) link->rcvbuf;
uint32_t totlen = ntohl(hdr->totlen);
uint16_t type = ntohs(hdr->type);
if (type < CLUSTERMSG_TYPE_COUNT)
server.cluster->stats_bus_messages_received[type]++;
serverLog(LL_DEBUG,"--- Processing packet of type %d, %lu bytes",
type, (unsigned long) totlen);
/* Perform sanity checks */
if (totlen < 16) return 1; /* At least signature, version, totlen, count. */
if (totlen > sdslen(link->rcvbuf)) return 1;
if (ntohs(hdr->ver) != CLUSTER_PROTO_VER) {
/* Can't handle messages of different versions. */
return 1;
}
uint16_t flags = ntohs(hdr->flags);
uint64_t senderCurrentEpoch = 0, senderConfigEpoch = 0;
clusterNode *sender;
if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_PONG ||
type == CLUSTERMSG_TYPE_MEET)
{
uint16_t count = ntohs(hdr->count);
uint32_t explen; /* expected length of this packet */
explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
explen += (sizeof(clusterMsgDataGossip)*count);
if (totlen != explen) return 1;
} else if (type == CLUSTERMSG_TYPE_FAIL) {
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
explen += sizeof(clusterMsgDataFail);
if (totlen != explen) return 1;
} else if (type == CLUSTERMSG_TYPE_PUBLISH) {
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
explen += sizeof(clusterMsgDataPublish) -
8 +
ntohl(hdr->data.publish.msg.channel_len) +
ntohl(hdr->data.publish.msg.message_len);
if (totlen != explen) return 1;
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST ||
type == CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK ||
type == CLUSTERMSG_TYPE_MFSTART)
{
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
if (totlen != explen) return 1;
} else if (type == CLUSTERMSG_TYPE_UPDATE) {
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
explen += sizeof(clusterMsgDataUpdate);
if (totlen != explen) return 1;
} else if (type == CLUSTERMSG_TYPE_MODULE) {
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
explen += sizeof(clusterMsgDataPublish) -
3 + ntohl(hdr->data.module.msg.len);
if (totlen != explen) return 1;
}
/* Check if the sender is a known node. */
sender = clusterLookupNode(hdr->sender);
if (sender && !nodeInHandshake(sender)) {
/* Update our curretEpoch if we see a newer epoch in the cluster. */
senderCurrentEpoch = ntohu64(hdr->currentEpoch);
senderConfigEpoch = ntohu64(hdr->configEpoch);
if (senderCurrentEpoch > server.cluster->currentEpoch)
server.cluster->currentEpoch = senderCurrentEpoch;
/* Update the sender configEpoch if it is publishing a newer one. */
if (senderConfigEpoch > sender->configEpoch) {
sender->configEpoch = senderConfigEpoch;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_FSYNC_CONFIG);
}
/* Update the replication offset info for this node. */
sender->repl_offset = ntohu64(hdr->offset);
sender->repl_offset_time = mstime();
/* If we are a slave performing a manual failover and our master
* sent its offset while already paused, populate the MF state. */
if (server.cluster->mf_end &&
nodeIsSlave(myself) &&
myself->slaveof == sender &&
hdr->mflags[0] & CLUSTERMSG_FLAG0_PAUSED &&
server.cluster->mf_master_offset == 0)
{
server.cluster->mf_master_offset = sender->repl_offset;
serverLog(LL_WARNING,
"Received replication offset for paused "
"master manual failover: %lld",
server.cluster->mf_master_offset);
}
}
/* Initial processing of PING and MEET requests replying with a PONG. */
if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_MEET) {
serverLog(LL_DEBUG,"Ping packet received: %p", (void*)link->node);
/* We use incoming MEET messages in order to set the address
* for 'myself', since only other cluster nodes will send us
* MEET messages on handshakes, when the cluster joins, or
* later if we changed address, and those nodes will use our
* official address to connect to us. So by obtaining this address
* from the socket is a simple way to discover / update our own
* address in the cluster without it being hardcoded in the config.
*
* However if we don't have an address at all, we update the address
* even with a normal PING packet. If it's wrong it will be fixed
* by MEET later. */
if ((type == CLUSTERMSG_TYPE_MEET || myself->ip[0] == '\0') &&
server.cluster_announce_ip == NULL)
{
char ip[NET_IP_STR_LEN];
if (connSockName(link->conn,ip,sizeof(ip),NULL) != -1 &&
strcmp(ip,myself->ip))
{
memcpy(myself->ip,ip,NET_IP_STR_LEN);
serverLog(LL_WARNING,"IP address for this node updated to %s",
myself->ip);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
}
}
/* Add this node if it is new for us and the msg type is MEET.
* In this stage we don't try to add the node with the right
* flags, slaveof pointer, and so forth, as this details will be
* resolved when we'll receive PONGs from the node. */
if (!sender && type == CLUSTERMSG_TYPE_MEET) {
clusterNode *node;
node = createClusterNode(NULL,CLUSTER_NODE_HANDSHAKE);
nodeIp2String(node->ip,link,hdr->myip);
node->port = ntohs(hdr->port);
node->cport = ntohs(hdr->cport);
clusterAddNode(node);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
}
/* If this is a MEET packet from an unknown node, we still process
* the gossip section here since we have to trust the sender because
* of the message type. */
if (!sender && type == CLUSTERMSG_TYPE_MEET)
clusterProcessGossipSection(hdr,link);
/* Anyway reply with a PONG */
clusterSendPing(link,CLUSTERMSG_TYPE_PONG);
}
/* PING, PONG, MEET: process config information. */
if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_PONG ||
type == CLUSTERMSG_TYPE_MEET)
{
serverLog(LL_DEBUG,"%s packet received: %p",
type == CLUSTERMSG_TYPE_PING ? "ping" : "pong",
(void*)link->node);
if (link->node) {
if (nodeInHandshake(link->node)) {
/* If we already have this node, try to change the
* IP/port of the node with the new one. */
if (sender) {
serverLog(LL_VERBOSE,
"Handshake: we already know node %.40s, "
"updating the address if needed.", sender->name);
if (nodeUpdateAddressIfNeeded(sender,link,hdr))
{
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
}
/* Free this node as we already have it. This will
* cause the link to be freed as well. */
clusterDelNode(link->node);
return 0;
}
/* First thing to do is replacing the random name with the
* right node name if this was a handshake stage. */
clusterRenameNode(link->node, hdr->sender);
serverLog(LL_DEBUG,"Handshake with node %.40s completed.",
link->node->name);
link->node->flags &= ~CLUSTER_NODE_HANDSHAKE;
link->node->flags |= flags&(CLUSTER_NODE_MASTER|CLUSTER_NODE_SLAVE);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
} else if (memcmp(link->node->name,hdr->sender,
CLUSTER_NAMELEN) != 0)
{
/* If the reply has a non matching node ID we
* disconnect this node and set it as not having an associated
* address. */
serverLog(LL_DEBUG,"PONG contains mismatching sender ID. About node %.40s added %d ms ago, having flags %d",
link->node->name,
(int)(mstime()-(link->node->ctime)),
link->node->flags);
link->node->flags |= CLUSTER_NODE_NOADDR;
link->node->ip[0] = '\0';
link->node->port = 0;
link->node->cport = 0;
freeClusterLink(link);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
return 0;
}
}
/* Copy the CLUSTER_NODE_NOFAILOVER flag from what the sender
* announced. This is a dynamic flag that we receive from the
* sender, and the latest status must be trusted. We need it to
* be propagated because the slave ranking used to understand the
* delay of each slave in the voting process, needs to know
* what are the instances really competing. */
if (sender) {
int nofailover = flags & CLUSTER_NODE_NOFAILOVER;
sender->flags &= ~CLUSTER_NODE_NOFAILOVER;
sender->flags |= nofailover;
}
/* Update the node address if it changed. */
if (sender && type == CLUSTERMSG_TYPE_PING &&
!nodeInHandshake(sender) &&
nodeUpdateAddressIfNeeded(sender,link,hdr))
{
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
}
/* Update our info about the node */
if (link->node && type == CLUSTERMSG_TYPE_PONG) {
link->node->pong_received = mstime();
link->node->ping_sent = 0;
/* The PFAIL condition can be reversed without external
* help if it is momentary (that is, if it does not
* turn into a FAIL state).
*
* The FAIL condition is also reversible under specific
* conditions detected by clearNodeFailureIfNeeded(). */
if (nodeTimedOut(link->node)) {
link->node->flags &= ~CLUSTER_NODE_PFAIL;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
} else if (nodeFailed(link->node)) {
clearNodeFailureIfNeeded(link->node);
}
}
/* Check for role switch: slave -> master or master -> slave. */
if (sender) {
if (!memcmp(hdr->slaveof,CLUSTER_NODE_NULL_NAME,
sizeof(hdr->slaveof)))
{
/* Node is a master. */
clusterSetNodeAsMaster(sender);
} else {
/* Node is a slave. */
clusterNode *master = clusterLookupNode(hdr->slaveof);
if (nodeIsMaster(sender)) {
/* Master turned into a slave! Reconfigure the node. */
clusterDelNodeSlots(sender);
sender->flags &= ~(CLUSTER_NODE_MASTER|
CLUSTER_NODE_MIGRATE_TO);
sender->flags |= CLUSTER_NODE_SLAVE;
/* Update config and state. */
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
}
/* Master node changed for this slave? */
if (master && sender->slaveof != master) {
if (sender->slaveof)
clusterNodeRemoveSlave(sender->slaveof,sender);
clusterNodeAddSlave(master,sender);
sender->slaveof = master;
/* Update config. */
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
}
}
}
/* Update our info about served slots.
*
* Note: this MUST happen after we update the master/slave state
* so that CLUSTER_NODE_MASTER flag will be set. */
/* Many checks are only needed if the set of served slots this
* instance claims is different compared to the set of slots we have
* for it. Check this ASAP to avoid other computational expansive
* checks later. */
clusterNode *sender_master = NULL; /* Sender or its master if slave. */
int dirty_slots = 0; /* Sender claimed slots don't match my view? */
if (sender) {
sender_master = nodeIsMaster(sender) ? sender : sender->slaveof;
if (sender_master) {
dirty_slots = memcmp(sender_master->slots,
hdr->myslots,sizeof(hdr->myslots)) != 0;
}
}
/* 1) If the sender of the message is a master, and we detected that
* the set of slots it claims changed, scan the slots to see if we
* need to update our configuration. */
if (sender && nodeIsMaster(sender) && dirty_slots)
clusterUpdateSlotsConfigWith(sender,senderConfigEpoch,hdr->myslots);
/* 2) We also check for the reverse condition, that is, the sender
* claims to serve slots we know are served by a master with a
* greater configEpoch. If this happens we inform the sender.
*
* This is useful because sometimes after a partition heals, a
* reappearing master may be the last one to claim a given set of
* hash slots, but with a configuration that other instances know to
* be deprecated. Example:
*
* A and B are master and slave for slots 1,2,3.
* A is partitioned away, B gets promoted.
* B is partitioned away, and A returns available.
*
* Usually B would PING A publishing its set of served slots and its
* configEpoch, but because of the partition B can't inform A of the
* new configuration, so other nodes that have an updated table must
* do it. In this way A will stop to act as a master (or can try to
* failover if there are the conditions to win the election). */
if (sender && dirty_slots) {
int j;
for (j = 0; j < CLUSTER_SLOTS; j++) {
if (bitmapTestBit(hdr->myslots,j)) {
if (server.cluster->slots[j] == sender ||
server.cluster->slots[j] == NULL) continue;
if (server.cluster->slots[j]->configEpoch >
senderConfigEpoch)
{
serverLog(LL_VERBOSE,
"Node %.40s has old slots configuration, sending "
"an UPDATE message about %.40s",
sender->name, server.cluster->slots[j]->name);
clusterSendUpdate(sender->link,
server.cluster->slots[j]);
/* TODO: instead of exiting the loop send every other
* UPDATE packet for other nodes that are the new owner
* of sender's slots. */
break;
}
}
}
}
/* If our config epoch collides with the sender's try to fix
* the problem. */
if (sender &&
nodeIsMaster(myself) && nodeIsMaster(sender) &&
senderConfigEpoch == myself->configEpoch)
{
clusterHandleConfigEpochCollision(sender);
}
/* Get info from the gossip section */
if (sender) clusterProcessGossipSection(hdr,link);
} else if (type == CLUSTERMSG_TYPE_FAIL) {
clusterNode *failing;
if (sender) {
failing = clusterLookupNode(hdr->data.fail.about.nodename);
if (failing &&
!(failing->flags & (CLUSTER_NODE_FAIL|CLUSTER_NODE_MYSELF)))
{
serverLog(LL_NOTICE,
"FAIL message received from %.40s about %.40s",
hdr->sender, hdr->data.fail.about.nodename);
failing->flags |= CLUSTER_NODE_FAIL;
failing->fail_time = mstime();
failing->flags &= ~CLUSTER_NODE_PFAIL;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
}
} else {
serverLog(LL_NOTICE,
"Ignoring FAIL message from unknown node %.40s about %.40s",
hdr->sender, hdr->data.fail.about.nodename);
}
} else if (type == CLUSTERMSG_TYPE_PUBLISH) {
robj *channel, *message;
uint32_t channel_len, message_len;
/* Don't bother creating useless objects if there are no
* Pub/Sub subscribers. */
if (dictSize(server.pubsub_channels) ||
listLength(server.pubsub_patterns))
{
channel_len = ntohl(hdr->data.publish.msg.channel_len);
message_len = ntohl(hdr->data.publish.msg.message_len);
channel = createStringObject(
(char*)hdr->data.publish.msg.bulk_data,channel_len);
message = createStringObject(
(char*)hdr->data.publish.msg.bulk_data+channel_len,
message_len);
pubsubPublishMessage(channel,message);
decrRefCount(channel);
decrRefCount(message);
}
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST) {
if (!sender) return 1; /* We don't know that node. */
clusterSendFailoverAuthIfNeeded(sender,hdr);
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK) {
if (!sender) return 1; /* We don't know that node. */
/* We consider this vote only if the sender is a master serving
* a non zero number of slots, and its currentEpoch is greater or
* equal to epoch where this node started the election. */
if (nodeIsMaster(sender) && sender->numslots > 0 &&
senderCurrentEpoch >= server.cluster->failover_auth_epoch)
{
server.cluster->failover_auth_count++;
/* Maybe we reached a quorum here, set a flag to make sure
* we check ASAP. */
clusterDoBeforeSleep(CLUSTER_TODO_HANDLE_FAILOVER);
}
} else if (type == CLUSTERMSG_TYPE_MFSTART) {
/* This message is acceptable only if I'm a master and the sender
* is one of my slaves. */
if (!sender || sender->slaveof != myself) return 1;
/* Manual failover requested from slaves. Initialize the state
* accordingly. */
resetManualFailover();
server.cluster->mf_end = mstime() + CLUSTER_MF_TIMEOUT;
server.cluster->mf_slave = sender;
pauseClients(mstime()+(CLUSTER_MF_TIMEOUT*2));
serverLog(LL_WARNING,"Manual failover requested by replica %.40s.",
sender->name);
} else if (type == CLUSTERMSG_TYPE_UPDATE) {
clusterNode *n; /* The node the update is about. */
uint64_t reportedConfigEpoch =
ntohu64(hdr->data.update.nodecfg.configEpoch);
if (!sender) return 1; /* We don't know the sender. */
n = clusterLookupNode(hdr->data.update.nodecfg.nodename);
if (!n) return 1; /* We don't know the reported node. */
if (n->configEpoch >= reportedConfigEpoch) return 1; /* Nothing new. */
/* If in our current config the node is a slave, set it as a master. */
if (nodeIsSlave(n)) clusterSetNodeAsMaster(n);
/* Update the node's configEpoch. */
n->configEpoch = reportedConfigEpoch;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_FSYNC_CONFIG);
/* Check the bitmap of served slots and update our
* config accordingly. */
clusterUpdateSlotsConfigWith(n,reportedConfigEpoch,
hdr->data.update.nodecfg.slots);
} else if (type == CLUSTERMSG_TYPE_MODULE) {
if (!sender) return 1; /* Protect the module from unknown nodes. */
/* We need to route this message back to the right module subscribed
* for the right message type. */
uint64_t module_id = hdr->data.module.msg.module_id; /* Endian-safe ID */
uint32_t len = ntohl(hdr->data.module.msg.len);
uint8_t type = hdr->data.module.msg.type;
unsigned char *payload = hdr->data.module.msg.bulk_data;
moduleCallClusterReceivers(sender->name,module_id,type,payload,len);
} else {
serverLog(LL_WARNING,"Received unknown packet type: %d", type);
}
return 1;
}
/* Process the gossip section of PING or PONG packets.
* Note that this function assumes that the packet is already sanity-checked
* by the caller, not in the content of the gossip section, but in the
* length. */
void clusterProcessGossipSection(clusterMsg *hdr, clusterLink *link) {
uint16_t count = ntohs(hdr->count);
clusterMsgDataGossip *g = (clusterMsgDataGossip*) hdr->data.ping.gossip;
clusterNode *sender = link->node ? link->node : clusterLookupNode(hdr->sender);
while(count--) {
uint16_t flags = ntohs(g->flags);
clusterNode *node;
sds ci;
if (server.verbosity == LL_DEBUG) {
ci = representClusterNodeFlags(sdsempty(), flags);
serverLog(LL_DEBUG,"GOSSIP %.40s %s:%[email protected]%d %s",
g->nodename,
g->ip,
ntohs(g->port),
ntohs(g->cport),
ci);
sdsfree(ci);
}
/* Update our state accordingly to the gossip sections */
node = clusterLookupNode(g->nodename);
if (node) {
/* We already know this node.
Handle failure reports, only when the sender is a master. */
if (sender && nodeIsMaster(sender) && node != myself) {
if (flags & (CLUSTER_NODE_FAIL|CLUSTER_NODE_PFAIL)) {
if (clusterNodeAddFailureReport(node,sender)) {
serverLog(LL_VERBOSE,
"Node %.40s reported node %.40s as not reachable.",
sender->name, node->name);
}
markNodeAsFailingIfNeeded(node);
} else {
if (clusterNodeDelFailureReport(node,sender)) {
serverLog(LL_VERBOSE,
"Node %.40s reported node %.40s is back online.",
sender->name, node->name);
}
}
}
/* If from our POV the node is up (no failure flags are set),
* we have no pending ping for the node, nor we have failure
* reports for this node, update the last pong time with the
* one we see from the other nodes. */
if (!(flags & (CLUSTER_NODE_FAIL|CLUSTER_NODE_PFAIL)) &&
node->ping_sent == 0 &&
clusterNodeFailureReportsCount(node) == 0)
{
mstime_t pongtime = ntohl(g->pong_received);
pongtime *= 1000; /* Convert back to milliseconds. */
/* Replace the pong time with the received one only if
* it's greater than our view but is not in the future
* (with 500 milliseconds tolerance) from the POV of our
* clock. */
if (pongtime <= (server.mstime+500) &&
pongtime > node->pong_received)
{
node->pong_received = pongtime;
}
}
/* If we already know this node, but it is not reachable, and
* we see a different address in the gossip section of a node that
* can talk with this other node, update the address, disconnect
* the old link if any, so that we'll attempt to connect with the
* new address. */
if (node->flags & (CLUSTER_NODE_FAIL|CLUSTER_NODE_PFAIL) &&
!(flags & CLUSTER_NODE_NOADDR) &&
!(flags & (CLUSTER_NODE_FAIL|CLUSTER_NODE_PFAIL)) &&
(strcasecmp(node->ip,g->ip) ||
node->port != ntohs(g->port) ||
node->cport != ntohs(g->cport)))
{
if (node->link) freeClusterLink(node->link);
memcpy(node->ip,g->ip,NET_IP_STR_LEN);
node->port = ntohs(g->port);
node->cport = ntohs(g->cport);
node->flags &= ~CLUSTER_NODE_NOADDR;
}
} else {
/* If it's not in NOADDR state and we don't have it, we
* start a handshake process against this IP/PORT pairs.
*
* Note that we require that the sender of this gossip message
* is a well known node in our cluster, otherwise we risk
* joining another cluster. */
if (sender &&
!(flags & CLUSTER_NODE_NOADDR) &&
!clusterBlacklistExists(g->nodename))
{
clusterStartHandshake(g->ip,ntohs(g->port),ntohs(g->cport));
}
}
/* Next node * /
g++;
}
}
在Redis中有四類基本的訊息，Meet、Ping、Pong和Fail，它們的功能為：
Meet： 利用“cluster meet ip port”命令，叢集節點邀請新節點加入。
Ping ：節點心跳，傳送規則是上面提到的Pong超時時間的一半，就傳送，訊息含已知的兩個節點資訊（1自己+2已知=3）。
Pong ：節點收到 ping 訊息的迴應訊息，訊息含已知的兩個節點資訊。
Fail： ping沒有迴應，會向叢集所有節點廣播該節點疑似下線的訊息。其他節點收到訊息後標記已疑似下線，當標記數量超過半數，節點正式下線。
上面這兩個函式是叢集通訊中的資料處理的兩個主要函式，一個是對包的資訊管理，一個是對個具體的資訊的解析。
二、網路管理
1、基本訊息的通訊：
主要是上面提到的四類訊息：
MEET：
void clusterCommand(client *c) {
if (server.cluster_enabled == 0) {
addReplyError(c,"This instance has cluster support disabled");
return;
}
if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"help")) {
......
} else if (!strcasecmp(c->argv[1]->ptr,"meet") && (c->argc == 4 || c->argc == 5)) {
/* CLUSTER MEET <ip> <port> [cport] */
long long port, cport;
if (getLongLongFromObject(c->argv[3], &port) != C_OK) {
addReplyErrorFormat(c,"Invalid TCP base port specified: %s",
(char*)c->argv[3]->ptr);
return;
}
if (c->argc == 5) {
if (getLongLongFromObject(c->argv[4], &cport) != C_OK) {
addReplyErrorFormat(c,"Invalid TCP bus port specified: %s",
(char*)c->argv[4]->ptr);
return;
}
} else {
cport = port + CLUSTER_PORT_INCR;
}
//在此函式中處理MEET
if (clusterStartHandshake(c->argv[2]->ptr,port,cport) == 0 &&
errno == EINVAL)
{
addReplyErrorFormat(c,"Invalid node address specified: %s:%s",
(char*)c->argv[2]->ptr, (char*)c->argv[3]->ptr);
} else {
addReply(c,shared.ok);
}
}
......
}
int clusterStartHandshake(char *ip, int port, int cport) {
clusterNode *n;
char norm_ip[NET_IP_STR_LEN];
struct sockaddr_storage sa;
/* IP sanity check */
if (inet_pton(AF_INET,ip,
&(((struct sockaddr_in *)&sa)->sin_addr)))
{
sa.ss_family = AF_INET;
} else if (inet_pton(AF_INET6,ip,
&(((struct sockaddr_in6 *)&sa)->sin6_addr)))
{
sa.ss_family = AF_INET6;
} else {
errno = EINVAL;
return 0;
}
/* Port sanity check */
if (port <= 0 || port > 65535 || cport <= 0 || cport > 65535) {
errno = EINVAL;
return 0;
}
/* Set norm_ip as the normalized string representation of the node
* IP address. */
memset(norm_ip,0,NET_IP_STR_LEN);
if (sa.ss_family == AF_INET)
inet_ntop(AF_INET,
(void*)&(((struct sockaddr_in *)&sa)->sin_addr),
norm_ip,NET_IP_STR_LEN);
else
inet_ntop(AF_INET6,
(void*)&(((struct sockaddr_in6 *)&sa)->sin6_addr),
norm_ip,NET_IP_STR_LEN);
//判斷，為了防止重複向同一節點通訊
if (clusterHandshakeInProgress(norm_ip,port,cport)) {
errno = EAGAIN;
return 0;
}
//建立隨機節點，準備通訊
/* Add the node with a random address (NULL as first argument to
* createClusterNode()). Everything will be fixed during the
* handshake. * /
n = createClusterNode(NULL,CLUSTER_NODE_HANDSHAKE|CLUSTER_NODE_MEET);
memcpy(n->ip,norm_ip,sizeof(n->ip));
n->port = port;
n->cport = cport;
clusterAddNode(n);
return 1;
}
//真正的傳送在定時器中
void clusterCron(){
......
handshake_timeout = server.cluster_node_timeout;
if (handshake_timeout < 1000) handshake_timeout = 1000;
/* Update myself flags. */
clusterUpdateMyselfFlags();
/* Check if we have disconnected nodes and re-establish the connection.
* Also update a few stats while we are here, that can be used to make
* better decisions in other part of the code. */
di = dictGetSafeIterator(server.cluster->nodes);
server.cluster->stats_pfail_nodes = 0;
while((de = dictNext(di)) != NULL) {
clusterNode *node = dictGetVal(de);
/* Not interested in reconnecting the link with myself or nodes
* for which we have no address. */
if (node->flags & (CLUSTER_NODE_MYSELF|CLUSTER_NODE_NOADDR)) continue;
if (node->flags & CLUSTER_NODE_PFAIL)
server.cluster->stats_pfail_nodes++;
/* A Node in HANDSHAKE state has a limited lifespan equal to the
* configured node timeout. */
if (nodeInHandshake(node) && now - node->ctime > handshake_timeout) {
clusterDelNode(node);
continue;
}
if (node->link == NULL) {
clusterLink *link = createClusterLink(node);
link->conn = server.tls_cluster ? connCreateTLS() : connCreateSocket();
connSetPrivateData(link->conn, link);
if (connConnect(link->conn, node->ip, node->cport, NET_FIRST_BIND_ADDR,
clusterLinkConnectHandler) == -1) {
/* We got a synchronous error from connect before
* clusterSendPing() had a chance to be called.
* If node->ping_sent is zero, failure detection can't work,
* so we claim we actually sent a ping now (that will
* be really sent as soon as the link is obtained). * /
if (node->ping_sent == 0) node->ping_sent = mstime();
serverLog(LL_DEBUG, "Unable to connect to "
"Cluster Node [%s]:%d -> %s", node->ip,
node->cport, server.neterr);
freeClusterLink(link);
continue;
}
node->link = link;
}
}
dictReleaseIterator(di);
......
}
void clusterLinkConnectHandler(connection *conn) {
clusterLink *link = connGetPrivateData(conn);
clusterNode *node = link->node;
/* Check if connection succeeded */
if (connGetState(conn) != CONN_STATE_CONNECTED) {
serverLog(LL_VERBOSE, "Connection with Node %.40s at %s:%d failed: %s",
node->name, node->ip, node->cport,
connGetLastError(conn));
freeClusterLink(link);
return;
}
/* Register a read handler from now on */
connSetReadHandler(conn, clusterReadHandler);
/* Queue a PING in the new connection ASAP: this is crucial
* to avoid false positives in failure detection.
*
* If the node is flagged as MEET, we send a MEET message instead
* of a PING one, to force the receiver to add us in its node
* table. */
mstime_t old_ping_sent = node->ping_sent;
clusterSendPing(link, node->flags & CLUSTER_NODE_MEET ?
CLUSTERMSG_TYPE_MEET : CLUSTERMSG_TYPE_PING);
if (old_ping_sent) {
/* If there was an active ping before the link was
* disconnected, we want to restore the ping time, otherwise
* replaced by the clusterSendPing() call. */
node->ping_sent = old_ping_sent;
}
/* We can clear the flag after the first packet is sent.
* If we'll never receive a PONG, we'll never send new packets
* to this node. Instead after the PONG is received and we
* are no longer in meet/handshake status, we want to send
* normal PING packets. */
node->flags &= ~CLUSTER_NODE_MEET;
serverLog(LL_DEBUG,"Connecting with Node %.40s at %s:%d",
node->name, node->ip, node->cport);
}
//PONG
int clusterProcessPacket(clusterLink *link) {
......
if (sender && !nodeInHandshake(sender)) {
/* Update our curretEpoch if we see a newer epoch in the cluster. */
senderCurrentEpoch = ntohu64(hdr->currentEpoch);
senderConfigEpoch = ntohu64(hdr->configEpoch);
if (senderCurrentEpoch > server.cluster->currentEpoch)
server.cluster->currentEpoch = senderCurrentEpoch;
/* Update the sender configEpoch if it is publishing a newer one. */
if (senderConfigEpoch > sender->configEpoch) {
sender->configEpoch = senderConfigEpoch;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_FSYNC_CONFIG);
}
/* Update the replication offset info for this node. */
sender->repl_offset = ntohu64(hdr->offset);
sender->repl_offset_time = mstime();
/* If we are a slave performing a manual failover and our master
* sent its offset while already paused, populate the MF state. */
if (server.cluster->mf_end &&
nodeIsSlave(myself) &&
myself->slaveof == sender &&
hdr->mflags[0] & CLUSTERMSG_FLAG0_PAUSED &&
server.cluster->mf_master_offset == 0)
{
server.cluster->mf_master_offset = sender->repl_offset;
serverLog(LL_WARNING,
"Received replication offset for paused "
"master manual failover: %lld",
server.cluster->mf_master_offset);
}
}
/* Initial processing of PING and MEET requests replying with a PONG. */
if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_MEET) {
serverLog(LL_DEBUG,"Ping packet received: %p", (void*)link->node);
/* We use incoming MEET messages in order to set the address
* for 'myself', since only other cluster nodes will send us
* MEET messages on handshakes, when the cluster joins, or
* later if we changed address, and those nodes will use our
* official address to connect to us. So by obtaining this address
* from the socket is a simple way to discover / update our own
* address in the cluster without it being hardcoded in the config.
*
* However if we don't have an address at all, we update the address
* even with a normal PING packet. If it's wrong it will be fixed
* by MEET later. */
if ((type == CLUSTERMSG_TYPE_MEET || myself->ip[0] == '\0') &&
server.cluster_announce_ip == NULL)
{
char ip[NET_IP_STR_LEN];
if (connSockName(link->conn,ip,sizeof(ip),NULL) != -1 &&
strcmp(ip,myself->ip))
{
memcpy(myself->ip,ip,NET_IP_STR_LEN);
serverLog(LL_WARNING,"IP address for this node updated to %s",
myself->ip);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
}
}
/* Add this node if it is new for us and the msg type is MEET.
* In this stage we don't try to add the node with the right
* flags, slaveof pointer, and so forth, as this details will be
* resolved when we'll receive PONGs from the node. */
if (!sender && type == CLUSTERMSG_TYPE_MEET) {
clusterNode *node;
node = createClusterNode(NULL,CLUSTER_NODE_HANDSHAKE);
nodeIp2String(node->ip,link,hdr->myip);
node->port = ntohs(hdr->port);
node->cport = ntohs(hdr->cport);
clusterAddNode(node);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
}
/* If this is a MEET packet from an unknown node, we still process
* the gossip section here since we have to trust the sender because
* of the message type. */
if (!sender && type == CLUSTERMSG_TYPE_MEET)
clusterProcessGossipSection(hdr,link);
/* Anyway reply with a PONG */
clusterSendPing(link,CLUSTERMSG_TYPE_PONG);
}
......
}
void clusterSendPing(clusterLink *link, int type) {
unsigned char *buf;
clusterMsg *hdr;
int gossipcount = 0; /* Number of gossip sections added so far. */
int wanted; /* Number of gossip sections we want to append if possible. */
int totlen; /* Total packet length. */
/* freshnodes is the max number of nodes we can hope to append at all:
* nodes available minus two (ourself and the node we are sending the
* message to). However practically there may be less valid nodes since
* nodes in handshake state, disconnected, are not considered. */
int freshnodes = dictSize(server.cluster->nodes)-2;
/* How many gossip sections we want to add? 1/10 of the number of nodes
* and anyway at least 3. Why 1/10?
*
* If we have N masters, with N/10 entries, and we consider that in
* node_timeout we exchange with each other node at least 4 packets
* (we ping in the worst case in node_timeout/2 time, and we also
* receive two pings from the host), we have a total of 8 packets
* in the node_timeout*2 falure reports validity time. So we have
* that, for a single PFAIL node, we can expect to receive the following
* number of failure reports (in the specified window of time):
*
* PROB * GOSSIP_ENTRIES_PER_PACKET * TOTAL_PACKETS:
*
* PROB = probability of being featured in a single gossip entry,
* which is 1 / NUM_OF_NODES.
* ENTRIES = 10.
* TOTAL_PACKETS = 2 * 4 * NUM_OF_MASTERS.
*
* If we assume we have just masters (so num of nodes and num of masters
* is the same), with 1/10 we always get over the majority, and specifically
* 80% of the number of nodes, to account for many masters failing at the
* same time.
*
* Since we have non-voting slaves that lower the probability of an entry
* to feature our node, we set the number of entries per packet as
* 10% of the total nodes we have. */
wanted = floor(dictSize(server.cluster->nodes)/10);
if (wanted < 3) wanted = 3;
if (wanted > freshnodes) wanted = freshnodes;
/* Include all the nodes in PFAIL state, so that failure reports are
* faster to propagate to go from PFAIL to FAIL state. */
int pfail_wanted = server.cluster->stats_pfail_nodes;
/* Compute the maxium totlen to allocate our buffer. We'll fix the totlen
* later according to the number of gossip sections we really were able
* to put inside the packet. */
totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
totlen += (sizeof(clusterMsgDataGossip)*(wanted+pfail_wanted));
/* Note: clusterBuildMessageHdr() expects the buffer to be always at least
* sizeof(clusterMsg) or more. */
if (totlen < (int)sizeof(clusterMsg)) totlen = sizeof(clusterMsg);
buf = zcalloc(totlen);
hdr = (clusterMsg*) buf;
/* Populate the header. */
if (link->node && type == CLUSTERMSG_TYPE_PING)
link->node->ping_sent = mstime();
clusterBuildMessageHdr(hdr,type);
/* Populate the gossip fields */
int maxiterations = wanted*3;
while(freshnodes > 0 && gossipcount < wanted && maxiterations--) {
dictEntry *de = dictGetRandomKey(server.cluster->nodes);
clusterNode *this = dictGetVal(de);
/* Don't include this node: the whole packet header is about us
* already, so we just gossip about other nodes. */
if (this == myself) continue;
/* PFAIL nodes will be added later. */
if (this->flags & CLUSTER_NODE_PFAIL) continue;
/* In the gossip section don't include:
* 1) Nodes in HANDSHAKE state.
* 3) Nodes with the NOADDR flag set.
* 4) Disconnected nodes if they don't have configured slots.
*/
if (this->flags & (CLUSTER_NODE_HANDSHAKE|CLUSTER_NODE_NOADDR) ||
(this->link == NULL && this->numslots == 0))
{
freshnodes--; /* Tecnically not correct, but saves CPU. */
continue;
}
/* Do not add a node we already have. */
if (clusterNodeIsInGossipSection(hdr,gossipcount,this)) continue;
/* Add it */
clusterSetGossipEntry(hdr,gossipcount,this);
freshnodes--;
gossipcount++;
}
/* If there are PFAIL nodes, add them at the end. */
if (pfail_wanted) {
dictIterator *di;
dictEntry *de;
di = dictGetSafeIterator(server.cluster->nodes);
while((de = dictNext(di)) != NULL && pfail_wanted > 0) {
clusterNode *node = dictGetVal(de);
if (node->flags & CLUSTER_NODE_HANDSHAKE) continue;
if (node->flags & CLUSTER_NODE_NOADDR) continue;
if (!(node->flags & CLUSTER_NODE_PFAIL)) continue;
clusterSetGossipEntry(hdr,gossipcount,node);
freshnodes--;
gossipcount++;
/* We take the count of the slots we allocated, since the
* PFAIL stats may not match perfectly with the current number
* of PFAIL nodes. */
pfail_wanted--;
}
dictReleaseIterator(di);
}
/* Ready to send... fix the totlen fiend and queue the message in the
* output buffer. */
totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
totlen += (sizeof(clusterMsgDataGossip)*gossipcount);
hdr->count = htons(gossipcount);
hdr->totlen = htonl(totlen);
clusterSendMessage(link,buf,totlen);
zfree(buf);
}
//PING
while((de = dictNext(di)) != NULL) {
clusterNode *node = dictGetVal(de);
now = mstime(); /* Use an updated time at every iteration. */
mstime_t delay;
if (node->flags &
(CLUSTER_NODE_MYSELF|CLUSTER_NODE_NOADDR|CLUSTER_NODE_HANDSHAKE))
continue;
/* Orphaned master check, useful only if the current instance
* is a slave that may migrate to another master. */
if (nodeIsSlave(myself) && nodeIsMaster(node) && !nodeFailed(node)) {
int okslaves = clusterCountNonFailingSlaves(node);
/* A master is orphaned if it is serving a non-zero number of
* slots, have no working slaves, but used to have at least one
* slave, or failed over a master that used to have slaves. */
if (okslaves == 0 && node->numslots > 0 &&
node->flags & CLUSTER_NODE_MIGRATE_TO)
{
orphaned_masters++;
}
if (okslaves > max_slaves) max_slaves = okslaves;
if (nodeIsSlave(myself) && myself->slaveof == node)
this_slaves = okslaves;
}
/* If we are waiting for the PONG more than half the cluster
* timeout, reconnect the link: maybe there is a connection
* issue even if the node is alive. */
if (node->link && /* is connected */
now - node->link->ctime >
server.cluster_node_timeout && /* was not already reconnected */
node->ping_sent && /* we already sent a ping */
node->pong_received < node->ping_sent && /* still waiting pong */
/* and we are waiting for the pong more than timeout/2 */
now - node->ping_sent > server.cluster_node_timeout/2)
{
/* Disconnect the link, it will be reconnected automatically. */
freeClusterLink(node->link);
}
/* If we have currently no active ping in this instance, and the
* received PONG is older than half the cluster timeout, send
* a new ping now, to ensure all the nodes are pinged without
* a too big delay. */
if (node->link &&
node->ping_sent == 0 &&
(now - node->pong_received) > server.cluster_node_timeout/2)
{
//傳送PING
clusterSendPing(node->link, CLUSTERMSG_TYPE_PING);
continue;
}
......
}
主結點在收到PONG迴應後的處理：
int clusterProcessPacket(clusterLink *link) {
......
/* PING, PONG, MEET: process config information. */
if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_PONG ||
type == CLUSTERMSG_TYPE_MEET)
{
serverLog(LL_DEBUG,"%s packet received: %p",
type == CLUSTERMSG_TYPE_PING ? "ping" : "pong",
(void*)link->node);
if (link->node) {
if (nodeInHandshake(link->node)) {
/* If we already have this node, try to change the
* IP/port of the node with the new one. */
if (sender) {
serverLog(LL_VERBOSE,
"Handshake: we already know node %.40s, "
"updating the address if needed.", sender->name);
if (nodeUpdateAddressIfNeeded(sender,link,hdr))
{
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
}
/* Free this node as we already have it. This will
* cause the link to be freed as well. */
clusterDelNode(link->node);
return 0;
}
/* First thing to do is replacing the random name with the
* right node name if this was a handshake stage. */
clusterRenameNode(link->node, hdr->sender);
serverLog(LL_DEBUG,"Handshake with node %.40s completed.",
link->node->name);
link->node->flags &= ~CLUSTER_NODE_HANDSHAKE;
link->node->flags |= flags&(CLUSTER_NODE_MASTER|CLUSTER_NODE_SLAVE);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
} else if (memcmp(link->node->name,hdr->sender,
CLUSTER_NAMELEN) != 0)
{
/* If the reply has a non matching node ID we
* disconnect this node and set it as not having an associated
* address. */
serverLog(LL_DEBUG,"PONG contains mismatching sender ID. About node %.40s added %d ms ago, having flags %d",
link->node->name,
(int)(mstime()-(link->node->ctime)),
link->node->flags);
link->node->flags |= CLUSTER_NODE_NOADDR;
link->node->ip[0] = '\0';
link->node->port = 0;
link->node->cport = 0;
freeClusterLink(link);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
return 0;
}
}
if (sender) {
int nofailover = flags & CLUSTER_NODE_NOFAILOVER;
sender->flags &= ~CLUSTER_NODE_NOFAILOVER;
sender->flags |= nofailover;
}
/* Update the node address if it changed. */
if (sender && type == CLUSTERMSG_TYPE_PING &&
!nodeInHandshake(sender) &&
nodeUpdateAddressIfNeeded(sender,link,hdr))
{
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
}
/* Update our info about the node */
if (link->node && type == CLUSTERMSG_TYPE_PONG) {
link->node->pong_received = mstime();
link->node->ping_sent = 0;
/* The PFAIL condition can be reversed without external
* help if it is momentary (that is, if it does not
* turn into a FAIL state).
*
* The FAIL condition is also reversible under specific
* conditions detected by clearNodeFailureIfNeeded(). */
if (nodeTimedOut(link->node)) {
link->node->flags &= ~CLUSTER_NODE_PFAIL;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE);
} else if (nodeFailed(link->node)) {
clearNodeFailureIfNeeded(link->node);
}
}
......
}
英文註釋已經很清楚，這裡就不再翻譯一次了。
2、主從切換
當出現故障需要master/slaver切換時，需要有一套機制來保證安全性：
當slave發現自己的master變為FAIL狀態時，便嘗試進行Failover，以期成為新的master。由於掛掉的master可能會有多個slave，從而存在多個slave競爭成為master節點的過程， 其過程如下：
a、slave發現自己的master狀態成為FAIL
b、把本身記錄的叢集currentEpoch加1，並廣播FAILOVER_AUTH_REQUEST資訊
c、只有master節點會響應這個資訊並判斷請求者合法性，驗證通過迴應FAILOVER_AUTH_ACK，每一個epoch只發送一次ack
d、發起failover的slave查詢收到FAILOVER_AUTH_ACK的數量
e、超過半數後將自己變成新Master
f、然後廣播Pong通知其他叢集節點
和RAFT等分散式選主一樣，為保證選舉的成功概率，從節點並不是在主節點一進入 FAIL 狀態就立刻進行選舉操作，而是有一定的時間延遲，一定的延遲除確保我們等待FAIL狀態在叢集中傳播同時可以保證不會有多個Slave同時發起選舉操作。slave如果立即嘗試選舉，其它masters可能有較大概率未接收到FAIL狀態，導致會產生拒絕投票行為，引發選舉失敗。
延遲計算公式：
DELAY = 500ms + random(0 ~ 500ms) + SLAVE_RANK * 1000ms
SLAVE_RANK：slave已經從master複製資料的總量的rank。Rank越小代表已複製的資料越新，擁有最新資料的slave有可能率先發起選舉。看一下原始碼：
從節點發起選舉：（slaver節點配置為允許進行故障轉移）
void clusterCron(void) {
dictIterator *di;
dictEntry *de;
int update_state = 0;
int orphaned_masters; /* How many masters there are without ok slaves. */
int max_slaves; /* Max number of ok slaves for a single master. */
int this_slaves; /* Number of ok slaves for our master (if we are slave). */
mstime_t min_pong = 0, now = mstime();
clusterNode *min_pong_node = NULL;
static unsigned long long iteration = 0;
mstime_t handshake_timeout;
......
/* If we are a slave node but the replication is still turned off,
* enable it if we know the address of our master and it appears to
* be up. */
if (nodeIsSlave(myself) &&
server.masterhost == NULL &&
myself->slaveof &&
nodeHasAddr(myself->slaveof))
{
replicationSetMaster(myself->slaveof->ip, myself->slaveof->port);
}
/* Abourt a manual failover if the timeout is reached. */
manualFailoverCheckTimeout();
if (nodeIsSlave(myself)) {
clusterHandleManualFailover();
if (!(server.cluster_module_flags & CLUSTER_MODULE_FLAG_NO_FAILOVER))
clusterHandleSlaveFailover();
/* If there are orphaned slaves, and we are a slave among the masters
* with the max number of non-failing slaves, consider migrating to
* the orphaned masters. Note that it does not make sense to try
* a migration if there is no master with at least *two* working
* slaves. * /
if (orphaned_masters && max_slaves >= 2 && this_slaves == max_slaves)
clusterHandleSlaveMigration(max_slaves);
}
if (update_state || server.cluster->state == CLUSTER_FAIL)
clusterUpdateState();
}
void clusterHandleSlaveFailover(void) {
mstime_t data_age;
mstime_t auth_age = mstime() - server.cluster->failover_auth_time;
int needed_quorum = (server.cluster->size / 2) + 1;
int manual_failover = server.cluster->mf_end != 0 &&
server.cluster->mf_can_start;
mstime_t auth_timeout, auth_retry_time;
server.cluster->todo_before_sleep &= ~CLUSTER_TODO_HANDLE_FAILOVER;
/* Compute the failover timeout (the max time we have to send votes
* and wait for replies), and the failover retry time (the time to wait
* before trying to get voted again).
*
* Timeout is MAX(NODE_TIMEOUT*2,2000) milliseconds.
* Retry is two times the Timeout.
*/
auth_timeout = server.cluster_node_timeout*2;
if (auth_timeout < 2000) auth_timeout = 2000;
auth_retry_time = auth_timeout*2;
/* Pre conditions to run the function, that must be met both in case
* of an automatic or manual failover:
* 1) We are a slave.
* 2) Our master is flagged as FAIL, or this is a manual failover.
* 3) We don't have the no failover configuration set, and this is
* not a manual failover.
* 4) It is serving slots. */
if (nodeIsMaster(myself) ||
myself->slaveof == NULL ||
(!nodeFailed(myself->slaveof) && !manual_failover) ||
(server.cluster_slave_no_failover && !manual_failover) ||
myself->slaveof->numslots == 0)
{
/* There are no reasons to failover, so we set the reason why we
* are returning without failing over to NONE. */
server.cluster->cant_failover_reason = CLUSTER_CANT_FAILOVER_NONE;
return;
}
/* Set data_age to the number of seconds we are disconnected from
* the master. */
if (server.repl_state == REPL_STATE_CONNECTED) {
data_age = (mstime_t)(server.unixtime - server.master->lastinteraction)
* 1000;
} else {
data_age = (mstime_t)(server.unixtime - server.repl_down_since) * 1000;
}
/* Remove the node timeout from the data age as it is fine that we are
* disconnected from our master at least for the time it was down to be
* flagged as FAIL, that's the baseline. */
if (data_age > server.cluster_node_timeout)
data_age -= server.cluster_node_timeout;
/* Check if our data is recent enough according to the slave validity
* factor configured by the user.
*
* Check bypassed for manual failovers. */
if (server.cluster_slave_validity_factor &&
data_age >
(((mstime_t)server.repl_ping_slave_period * 1000) +
(server.cluster_node_timeout * server.cluster_slave_validity_factor)))
{
if (!manual_failover) {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_DATA_AGE);
return;
}
}
/* If the previous failover attempt timedout and the retry time has
* elapsed, we can setup a new one. */
if (auth_age > auth_retry_time) {
server.cluster->failover_auth_time = mstime() +
500 + /* Fixed delay of 500 milliseconds, let FAIL msg propagate. */
random() % 500; /* Random delay between 0 and 500 milliseconds. */
server.cluster->failover_auth_count = 0;
server.cluster->failover_auth_sent = 0;
server.cluster->failover_auth_rank = clusterGetSlaveRank();
/* We add another delay that is proportional to the slave rank.
* Specifically 1 second * rank. This way slaves that have a probably
* less updated replication offset, are penalized. */
server.cluster->failover_auth_time +=
server.cluster->failover_auth_rank * 1000;
/* However if this is a manual failover, no delay is needed. */
if (server.cluster->mf_end) {
server.cluster->failover_auth_time = mstime();
server.cluster->failover_auth_rank = 0;
clusterDoBeforeSleep(CLUSTER_TODO_HANDLE_FAILOVER);
}
serverLog(LL_WARNING,
"Start of election delayed for %lld milliseconds "
"(rank #%d, offset %lld).",
server.cluster->failover_auth_time - mstime(),
server.cluster->failover_auth_rank,
replicationGetSlaveOffset());
/* Now that we have a scheduled election, broadcast our offset
* to all the other slaves so that they'll updated their offsets
* if our offset is better. */
clusterBroadcastPong(CLUSTER_BROADCAST_LOCAL_SLAVES);
return;
}
/* It is possible that we received more updated offsets from other
* slaves for the same master since we computed our election delay.
* Update the delay if our rank changed.
*
* Not performed if this is a manual failover. */
if (server.cluster->failover_auth_sent == 0 &&
server.cluster->mf_end == 0)
{
int newrank = clusterGetSlaveRank();
if (newrank > server.cluster->failover_auth_rank) {
long long added_delay =
(newrank - server.cluster->failover_auth_rank) * 1000;
server.cluster->failover_auth_time += added_delay;
server.cluster->failover_auth_rank = newrank;
serverLog(LL_WARNING,
"Replica rank updated to #%d, added %lld milliseconds of delay.",
newrank, added_delay);
}
}
/* Return ASAP if we can't still start the election. */
if (mstime() < server.cluster->failover_auth_time) {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_WAITING_DELAY);
return;
}
/* Return ASAP if the election is too old to be valid. */
if (auth_age > auth_timeout) {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_EXPIRED);
return;
}
/* Ask for votes if needed. */
if (server.cluster->failover_auth_sent == 0) {
server.cluster->currentEpoch++;
server.cluster->failover_auth_epoch = server.cluster->currentEpoch;
serverLog(LL_WARNING,"Starting a failover election for epoch %llu.",
(unsigned long long) server.cluster->currentEpoch);
clusterRequestFailoverAuth();
server.cluster->failover_auth_sent = 1;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE|
CLUSTER_TODO_FSYNC_CONFIG);
return; /* Wait for replies. */
}
/* Check if we reached the quorum. */
if (server.cluster->failover_auth_count >= needed_quorum) {
/* We have the quorum, we can finally failover the master. */
serverLog(LL_WARNING,
"Failover election won: I'm the new master.");
/* Update my configEpoch to the epoch of the election. */
if (myself->configEpoch < server.cluster->failover_auth_epoch) {
myself->configEpoch = server.cluster->failover_auth_epoch;
serverLog(LL_WARNING,
"configEpoch set to %llu after successful failover",
(unsigned long long) myself->configEpoch);
}
/* Take responsibility for the cluster slots. * /
clusterFailoverReplaceYourMaster();
} else {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_WAITING_VOTES);
}
}
此函式的註釋說明中指出有三個功能，一個是判斷是否為可操作的Slave節點，二是選舉Master，三是故障轉移。主要進行行一系列的工作準備：
a、needed_quorum選舉成功所需的票數， auth_timeout選舉超時時間，auth_retry_time選舉重試時間，auth_age失效時間等。
b、對前置條件的驗證，如是否為Slave節點，主節點Fail狀態位，允許轉移配置。
c、計算優先順序clusterGetSlaveRank()和選舉時間
d、選舉clusterRequestFailoverAuth
int clusterGetSlaveRank(void) {
long long myoffset;
int j, rank = 0;
clusterNode *master;
serverAssert(nodeIsSlave(myself));
master = myself->slaveof;
if (master == NULL) return 0; /* Never called by slaves without master. */
//計算偏移量
myoffset = replicationGetSlaveOffset();
for (j = 0; j < master->numslaves; j++)
if (master->slaves[j] != myself &&
!nodeCantFailover(master->slaves[j]) &&
master->slaves[j]->repl_offset > myoffset) rank++;
//將計算後的rank返回
return rank;
}
void clusterRequestFailoverAuth(void) {
clusterMsg buf[1];
clusterMsg *hdr = (clusterMsg*) buf;
uint32_t totlen;
//組建訊息
clusterBuildMessageHdr(hdr,CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST);
/* If this is a manual failover, set the CLUSTERMSG_FLAG0_FORCEACK bit
* in the header to communicate the nodes receiving the message that
* they should authorized the failover even if the master is working. * /
if (server.cluster->mf_end) hdr->mflags[0] |= CLUSTERMSG_FLAG0_FORCEACK;
totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
hdr->totlen = htonl(totlen);
//廣播訊息
clusterBroadcastMessage(buf,totlen);
}
主節點回應：
在上面的訊息包管理和解析兩個具體的函式裡有相關的程式碼
int clusterProcessPacket(clusterLink *link) {
clusterMsg *hdr = (clusterMsg*) link->rcvbuf;
......
else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST ||
type == CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK ||
type == CLUSTERMSG_TYPE_MFSTART)
{
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
if (totlen != explen) return 1;
......
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST) {
if (!sender) return 1; /* We don't know that node. */
clusterSendFailoverAuthIfNeeded(sender,hdr);
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK) {
if (!sender) return 1; /* We don't know that node. */
/* We consider this vote only if the sender is a master serving
* a non zero number of slots, and its currentEpoch is greater or
* equal to epoch where this node started the election. */
if (nodeIsMaster(sender) && sender->numslots > 0 &&
senderCurrentEpoch >= server.cluster->failover_auth_epoch)
{
server.cluster->failover_auth_count++;
/* Maybe we reached a quorum here, set a flag to make sure
* we check ASAP. */
clusterDoBeforeSleep(CLUSTER_TODO_HANDLE_FAILOVER);
}
}
......
}
這裡需要呼叫clusterSendFailoverAuthIfNeeded：
//對是否投票進行判斷
void clusterSendFailoverAuthIfNeeded(clusterNode *node, clusterMsg *request) {
clusterNode *master = node->slaveof;
uint64_t requestCurrentEpoch = ntohu64(request->currentEpoch);
uint64_t requestConfigEpoch = ntohu64(request->configEpoch);
unsigned char *claimed_slots = request->myslots;
int force_ack = request->mflags[0] & CLUSTERMSG_FLAG0_FORCEACK;
int j;
/* IF we are not a master serving at least 1 slot, we don't have the
* right to vote, as the cluster size in Redis Cluster is the number
* of masters serving at least one slot, and quorum is the cluster
* size + 1 */
if (nodeIsSlave(myself) || myself->numslots == 0) return;
/* Request epoch must be >= our currentEpoch.
* Note that it is impossible for it to actually be greater since
* our currentEpoch was updated as a side effect of receiving this
* request, if the request epoch was greater. */
if (requestCurrentEpoch < server.cluster->currentEpoch) {
serverLog(LL_WARNING,
"Failover auth denied to %.40s: reqEpoch (%llu) < curEpoch(%llu)",
node->name,
(unsigned long long) requestCurrentEpoch,
(unsigned long long) server.cluster->currentEpoch);
return;
}
/* I already voted for this epoch? Return ASAP. */
if (server.cluster->lastVoteEpoch == server.cluster->currentEpoch) {
serverLog(LL_WARNING,
"Failover auth denied to %.40s: already voted for epoch %llu",
node->name,
(unsigned long long) server.cluster->currentEpoch);
return;
}
/* Node must be a slave and its master down.
* The master can be non failing if the request is flagged
* with CLUSTERMSG_FLAG0_FORCEACK (manual failover). */
if (nodeIsMaster(node) || master == NULL ||
(!nodeFailed(master) && !force_ack))
{
if (nodeIsMaster(node)) {
serverLog(LL_WARNING,
"Failover auth denied to %.40s: it is a master node",
node->name);
} else if (master == NULL) {
serverLog(LL_WARNING,
"Failover auth denied to %.40s: I don't know its master",
node->name);
} else if (!nodeFailed(master)) {
serverLog(LL_WARNING,
"Failover auth denied to %.40s: its master is up",
node->name);
}
return;
}
/* We did not voted for a slave about this master for two
* times the node timeout. This is not strictly needed for correctness
* of the algorithm but makes the base case more linear. */
if (mstime() - node->slaveof->voted_time < server.cluster_node_timeout * 2)
{
serverLog(LL_WARNING,
"Failover auth denied to %.40s: "
"can't vote about this master before %lld milliseconds",
node->name,
(long long) ((server.cluster_node_timeout*2)-
(mstime() - node->slaveof->voted_time)));
return;
}
/* The slave requesting the vote must have a configEpoch for the claimed
* slots that is >= the one of the masters currently serving the same
* slots in the current configuration. */
for (j = 0; j < CLUSTER_SLOTS; j++) {
if (bitmapTestBit(claimed_slots, j) == 0) continue;
if (server.cluster->slots[j] == NULL ||
server.cluster->slots[j]->configEpoch <= requestConfigEpoch)
{
continue;
}
/* If we reached this point we found a slot that in our current slots
* is served by a master with a greater configEpoch than the one claimed
* by the slave requesting our vote. Refuse to vote for this slave. */
serverLog(LL_WARNING,
"Failover auth denied to %.40s: "
"slot %d epoch (%llu) > reqEpoch (%llu)",
node->name, j,
(unsigned long long) server.cluster->slots[j]->configEpoch,
(unsigned long long) requestConfigEpoch);
return;
}
/* We can vote for this slave. */
server.cluster->lastVoteEpoch = server.cluster->currentEpoch;
node->slaveof->voted_time = mstime();
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|CLUSTER_TODO_FSYNC_CONFIG);
clusterSendFailoverAuth(node);
serverLog(LL_WARNING, "Failover auth granted to %.40s for epoch %llu",
node->name, (unsigned long long) server.cluster->currentEpoch);
}
//最後傳送訊息
void clusterSendFailoverAuth(clusterNode *node) {
clusterMsg buf[1];
clusterMsg *hdr = (clusterMsg*) buf;
uint32_t totlen;
if (!node->link) return;
clusterBuildMessageHdr(hdr,CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK);
totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
hdr->totlen = htonl(totlen);
clusterSendMessage(node->link,(unsigned char*)buf,totlen);
}
從節點計算迴應數量：
int clusterProcessPacket(clusterLink *link) {
clusterMsg *hdr = (clusterMsg*) link->rcvbuf;
......
else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST ||
type == CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK ||
type == CLUSTERMSG_TYPE_MFSTART)
{
uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
if (totlen != explen) return 1;
......
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST) {
if (!sender) return 1; /* We don't know that node. */
clusterSendFailoverAuthIfNeeded(sender,hdr);
} else if (type == CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK) {
if (!sender) return 1; /* We don't know that node. */
/* We consider this vote only if the sender is a master serving
* a non zero number of slots, and its currentEpoch is greater or
* equal to epoch where this node started the election. */
if (nodeIsMaster(sender) && sender->numslots > 0 &&
senderCurrentEpoch >= server.cluster->failover_auth_epoch)
{
server.cluster->failover_auth_count++;
/* Maybe we reached a quorum here, set a flag to make sure
* we check ASAP. */
clusterDoBeforeSleep(CLUSTER_TODO_HANDLE_FAILOVER);
}
}
......
}
void clusterBeforeSleep(void) {
/* Handle failover, this is needed when it is likely that there is already
* the quorum from masters in order to react fast. */
if (server.cluster->todo_before_sleep & CLUSTER_TODO_HANDLE_FAILOVER)
clusterHandleSlaveFailover();
/* Update the cluster state. */
if (server.cluster->todo_before_sleep & CLUSTER_TODO_UPDATE_STATE)
clusterUpdateState();
/* Save the config, possibly using fsync. */
if (server.cluster->todo_before_sleep & CLUSTER_TODO_SAVE_CONFIG) {
int fsync = server.cluster->todo_before_sleep &
CLUSTER_TODO_FSYNC_CONFIG;
clusterSaveConfigOrDie(fsync);
}
/* Reset our flags (not strictly needed since every single function
* called for flags set should be able to clear its flag). */
server.cluster->todo_before_sleep = 0;
}
void clusterDoBeforeSleep(int flags) {
server.cluster->todo_before_sleep |= flags;
}
然後會呼叫：
void clusterHandleSlaveFailover(void) {
mstime_t data_age;
mstime_t auth_age = mstime() - server.cluster->failover_auth_time;
int needed_quorum = (server.cluster->size / 2) + 1;
int manual_failover = server.cluster->mf_end != 0 &&
server.cluster->mf_can_start;
mstime_t auth_timeout, auth_retry_time;
server.cluster->todo_before_sleep &= ~CLUSTER_TODO_HANDLE_FAILOVER;
/* Compute the failover timeout (the max time we have to send votes
* and wait for replies), and the failover retry time (the time to wait
* before trying to get voted again).
*
* Timeout is MAX(NODE_TIMEOUT*2,2000) milliseconds.
* Retry is two times the Timeout.
*/
auth_timeout = server.cluster_node_timeout*2;
if (auth_timeout < 2000) auth_timeout = 2000;
auth_retry_time = auth_timeout*2;
/* Pre conditions to run the function, that must be met both in case
* of an automatic or manual failover:
* 1) We are a slave.
* 2) Our master is flagged as FAIL, or this is a manual failover.
* 3) We don't have the no failover configuration set, and this is
* not a manual failover.
* 4) It is serving slots. */
if (nodeIsMaster(myself) ||
myself->slaveof == NULL ||
(!nodeFailed(myself->slaveof) && !manual_failover) ||
(server.cluster_slave_no_failover && !manual_failover) ||
myself->slaveof->numslots == 0)
{
/* There are no reasons to failover, so we set the reason why we
* are returning without failing over to NONE. */
server.cluster->cant_failover_reason = CLUSTER_CANT_FAILOVER_NONE;
return;
}
/* Set data_age to the number of seconds we are disconnected from
* the master. */
if (server.repl_state == REPL_STATE_CONNECTED) {
data_age = (mstime_t)(server.unixtime - server.master->lastinteraction)
* 1000;
} else {
data_age = (mstime_t)(server.unixtime - server.repl_down_since) * 1000;
}
/* Remove the node timeout from the data age as it is fine that we are
* disconnected from our master at least for the time it was down to be
* flagged as FAIL, that's the baseline. */
if (data_age > server.cluster_node_timeout)
data_age -= server.cluster_node_timeout;
/* Check if our data is recent enough according to the slave validity
* factor configured by the user.
*
* Check bypassed for manual failovers. */
if (server.cluster_slave_validity_factor &&
data_age >
(((mstime_t)server.repl_ping_slave_period * 1000) +
(server.cluster_node_timeout * server.cluster_slave_validity_factor)))
{
if (!manual_failover) {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_DATA_AGE);
return;
}
}
/* If the previous failover attempt timedout and the retry time has
* elapsed, we can setup a new one. */
if (auth_age > auth_retry_time) {
server.cluster->failover_auth_time = mstime() +
500 + /* Fixed delay of 500 milliseconds, let FAIL msg propagate. */
random() % 500; /* Random delay between 0 and 500 milliseconds. */
server.cluster->failover_auth_count = 0;
server.cluster->failover_auth_sent = 0;
server.cluster->failover_auth_rank = clusterGetSlaveRank();
/* We add another delay that is proportional to the slave rank.
* Specifically 1 second * rank. This way slaves that have a probably
* less updated replication offset, are penalized. */
server.cluster->failover_auth_time +=
server.cluster->failover_auth_rank * 1000;
/* However if this is a manual failover, no delay is needed. */
if (server.cluster->mf_end) {
server.cluster->failover_auth_time = mstime();
server.cluster->failover_auth_rank = 0;
clusterDoBeforeSleep(CLUSTER_TODO_HANDLE_FAILOVER);
}
serverLog(LL_WARNING,
"Start of election delayed for %lld milliseconds "
"(rank #%d, offset %lld).",
server.cluster->failover_auth_time - mstime(),
server.cluster->failover_auth_rank,
replicationGetSlaveOffset());
/* Now that we have a scheduled election, broadcast our offset
* to all the other slaves so that they'll updated their offsets
* if our offset is better. */
clusterBroadcastPong(CLUSTER_BROADCAST_LOCAL_SLAVES);
return;
}
/* It is possible that we received more updated offsets from other
* slaves for the same master since we computed our election delay.
* Update the delay if our rank changed.
*
* Not performed if this is a manual failover. */
if (server.cluster->failover_auth_sent == 0 &&
server.cluster->mf_end == 0)
{
int newrank = clusterGetSlaveRank();
if (newrank > server.cluster->failover_auth_rank) {
long long added_delay =
(newrank - server.cluster->failover_auth_rank) * 1000;
server.cluster->failover_auth_time += added_delay;
server.cluster->failover_auth_rank = newrank;
serverLog(LL_WARNING,
"Replica rank updated to #%d, added %lld milliseconds of delay.",
newrank, added_delay);
}
}
/* Return ASAP if we can't still start the election. */
if (mstime() < server.cluster->failover_auth_time) {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_WAITING_DELAY);
return;
}
/* Return ASAP if the election is too old to be valid. */
if (auth_age > auth_timeout) {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_EXPIRED);
return;
}
/* Ask for votes if needed. */
if (server.cluster->failover_auth_sent == 0) {
server.cluster->currentEpoch++;
server.cluster->failover_auth_epoch = server.cluster->currentEpoch;
serverLog(LL_WARNING,"Starting a failover election for epoch %llu.",
(unsigned long long) server.cluster->currentEpoch);
clusterRequestFailoverAuth();
server.cluster->failover_auth_sent = 1;
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE|
CLUSTER_TODO_FSYNC_CONFIG);
return; /* Wait for replies. */
}
/* Check if we reached the quorum. *///判斷選舉迴應的數量
if (server.cluster->failover_auth_count >= needed_quorum) {
/* We have the quorum, we can finally failover the master. */
serverLog(LL_WARNING,
"Failover election won: I'm the new master.");
/* Update my configEpoch to the epoch of the election. */
if (myself->configEpoch < server.cluster->failover_auth_epoch) {
myself->configEpoch = server.cluster->failover_auth_epoch;
serverLog(LL_WARNING,
"configEpoch set to %llu after successful failover",
(unsigned long long) myself->configEpoch);
}
/* Take responsibility for the cluster slots. * /
//達到約定數量即進行主從切換
clusterFailoverReplaceYourMaster();
} else {
clusterLogCantFailover(CLUSTER_CANT_FAILOVER_WAITING_VOTES);
}
}
3、節點故障轉移
判斷下線：
主觀判斷下線：節點間會進行定期的ping/pong訊息，如果二者不能成對，則傳送ping方就認為對方主動下線，將斷開網路連線。然後，節點會在再次執行ping訊息,如果超時，則將接收方置為疑似下線PFail，即主觀下線。
客觀判斷下線：節點會把疑似下線的節點通過標記傳送給網路，網路由此不斷轉發，當有一半以上持有一個以上的槽的主節點都記某節點下線後，即客觀下線，即正式標記為Fail。
二者的程式碼在：
void clusterCron(void) {
dictIterator *di;
dictEntry *de;
......
max_slaves = 0;
this_slaves = 0;
di = dictGetSafeIterator(server.cluster->nodes);
while((de = dictNext(di)) != NULL) {
clusterNode *node = dictGetVal(de);
now = mstime(); /* Use an updated time at every iteration. */
mstime_t delay;
if (node->flags &
(CLUSTER_NODE_MYSELF|CLUSTER_NODE_NOADDR|CLUSTER_NODE_HANDSHAKE))
continue;
......
/* If we are waiting for the PONG more than half the cluster
* timeout, reconnect the link: maybe there is a connection
* issue even if the node is alive. */
if (node->link && /* is connected */
now - node->link->ctime >
server.cluster_node_timeout && /* was not already reconnected */
node->ping_sent && /* we already sent a ping */
node->pong_received < node->ping_sent && /* still waiting pong */
/* and we are waiting for the pong more than timeout/2 */
now - node->ping_sent > server.cluster_node_timeout/2)
{
/* Disconnect the link, it will be reconnected automatically. */
//釋放連線
freeClusterLink(node->link);
}
/* If we have currently no active ping in this instance, and the
* received PONG is older than half the cluster timeout, send
* a new ping now, to ensure all the nodes are pinged without
* a too big delay. */
if (node->link &&
node->ping_sent == 0 &&
(now - node->pong_received) > server.cluster_node_timeout/2)
{
clusterSendPing(node->link, CLUSTERMSG_TYPE_PING);
continue;
}
/* If we are a master and one of the slaves requested a manual
* failover, ping it continuously. */
if (server.cluster->mf_end &&
nodeIsMaster(myself) &&
server.cluster->mf_slave == node &&
node->link)
{
clusterSendPing(node->link, CLUSTERMSG_TYPE_PING);
continue;
}
/* Check only if we have an active ping for this instance. */
if (node->ping_sent == 0) continue;
/* Compute the delay of the PONG. Note that if we already received
* the PONG, then node->ping_sent is zero, so can't reach this
* code at all. */
delay = now - node->ping_sent;
if (delay > server.cluster_node_timeout) {
/* Timeout reached. Set the node as possibly failing if it is
* not already in this state. */
if (!(node->flags & (CLUSTER_NODE_PFAIL|CLUSTER_NODE_FAIL))) {
serverLog(LL_DEBUG,"*** NODE %.40s possibly failing",
node->name);
node->flags |= CLUSTER_NODE_PFAIL;
update_state = 1;
}
}
}
dictReleaseIterator(di);
......
}
而判斷下線列表則在void clusterProcessGossipSection(clusterMsg * hdr, clusterLink * link) 這個函式中，前面已經提到 過：
void clusterProcessGossipSection(clusterMsg * hdr, clusterLink * link){
node = clusterLookupNode(g->nodename);
if (node) {
/* We already know this node.
Handle failure reports, only when the sender is a master. */
if (sender && nodeIsMaster(sender) && node != myself) {
if (flags & (CLUSTER_NODE_FAIL|CLUSTER_NODE_PFAIL)) {
if (clusterNodeAddFailureReport(node,sender)) {
serverLog(LL_VERBOSE,
"Node %.40s reported node %.40s as not reachable.",
sender->name, node->name);
}
markNodeAsFailingIfNeeded(node);//標記
} else {
if (clusterNodeDelFailureReport(node,sender)) {
serverLog(LL_VERBOSE,
"Node %.40s reported node %.40s is back online.",
sender->name, node->name);
}
}
}
}
正式下線後的故障恢復：
void clusterFailoverReplaceYourMaster(void) {
int j;
clusterNode *oldmaster = myself->slaveof;
if (nodeIsMaster(myself) || oldmaster == NULL) return;
/* 1) Turn this node into a master. */
clusterSetNodeAsMaster(myself);
replicationUnsetMaster();
/* 2) Claim all the slots assigned to our master. */
for (j = 0; j < CLUSTER_SLOTS; j++) {
if (clusterNodeGetSlotBit(oldmaster,j)) {
clusterDelSlot(j);
clusterAddSlot(myself,j);
}
}
/* 3) Update state and save config. */
clusterUpdateState();
clusterSaveConfigOrDie(1);
/* 4) Pong all the other nodes so that they can update the state
* accordingly and detect that we switched to master role. */
clusterBroadcastPong(CLUSTER_BROADCAST_ALL);
/* 5) If there was a manual failover in progress, clear the state. */
resetManualFailover();
}
4、槽的管理
在叢集建立成功後，就要進行槽位的分割槽和管理：
分配槽位：
void clusterCommand(client *c)
{
......
else if ((!strcasecmp(c->argv[1]->ptr,"addslots") ||
!strcasecmp(c->argv[1]->ptr,"delslots")) && c->argc >= 3)
{
/* CLUSTER ADDSLOTS <slot> [slot] ... */
/* CLUSTER DELSLOTS <slot> [slot] ... */
int j, slot;
unsigned char *slots = zmalloc(CLUSTER_SLOTS);
int del = !strcasecmp(c->argv[1]->ptr,"delslots");
memset(slots,0,CLUSTER_SLOTS);
/* Check that all the arguments are parseable and that all the
* slots are not already busy. */
for (j = 2; j < c->argc; j++) {
//獲得位置
if ((slot = getSlotOrReply(c,c->argv[j])) == -1) {
zfree(slots);
return;
}
if (del && server.cluster->slots[slot] == NULL) {
addReplyErrorFormat(c,"Slot %d is already unassigned", slot);
zfree(slots);
return;
} else if (!del && server.cluster->slots[slot]) {
addReplyErrorFormat(c,"Slot %d is already busy", slot);
zfree(slots);
return;
}
if (slots[slot]++ == 1) {
addReplyErrorFormat(c,"Slot %d specified multiple times",
(int)slot);
zfree(slots);
return;
}
}
for (j = 0; j < CLUSTER_SLOTS; j++) {
if (slots[j]) {
int retval;
//取消匯入狀態
/* If this slot was set as importing we can clear this
* state as now we are the real owner of the slot. */
if (server.cluster->importing_slots_from[j])
server.cluster->importing_slots_from[j] = NULL;
retval = del ? clusterDelSlot(j) :
clusterAddSlot(myself,j);
serverAssertWithInfo(c,NULL,retval == C_OK);
}
}
zfree(slots);
clusterDoBeforeSleep(CLUSTER_TODO_UPDATE_STATE|CLUSTER_TODO_SAVE_CONFIG);
addReply(c,shared.ok);
}
...
}
int clusterDelSlot(int slot) {
clusterNode *n = server.cluster->slots[slot];
if (!n) return C_ERR;
serverAssert(clusterNodeClearSlotBit(n,slot) == 1);
server.cluster->slots[slot] = NULL;
return C_OK;
}
int clusterAddSlot(clusterNode *n, int slot) {
if (server.cluster->slots[slot]) return C_ERR;
clusterNodeSetSlotBit(n,slot);
server.cluster->slots[slot] = n;
return C_OK;
}
int clusterNodeClearSlotBit(clusterNode *n, int slot) {
int old = bitmapTestBit(n->slots,slot);
bitmapClearBit(n->slots,slot);
if (old) n->numslots--;
return old;
}
上面的槽位新增，首先要判斷是新增還是刪除，如果刪除沒有指定的節點，返回錯誤，新增位置已經使用的節點，返回錯誤，指定多次同樣返回錯誤。
然後開始廣播此訊息到網路：
int clusterProcessPacket(clusterLink *link) {
...
/* Update our info about served slots.
*
* Note: this MUST happen after we update the master/slave state
* so that CLUSTER_NODE_MASTER flag will be set. */
/* Many checks are only needed if the set of served slots this
* instance claims is different compared to the set of slots we have
* for it. Check this ASAP to avoid other computational expansive
* checks later. */
clusterNode *sender_master = NULL; /* Sender or its master if slave. */
int dirty_slots = 0; /* Sender claimed slots don't match my view? */
if (sender) {
sender_master = nodeIsMaster(sender) ? sender : sender->slaveof;
if (sender_master) {
dirty_slots = memcmp(sender_master->slots,
hdr->myslots,sizeof(hdr->myslots)) != 0;
}
}
/* 1) If the sender of the message is a master, and we detected that
* the set of slots it claims changed, scan the slots to see if we
* need to update our configuration. */
if (sender && nodeIsMaster(sender) && dirty_slots)
clusterUpdateSlotsConfigWith(sender,senderConfigEpoch,hdr->myslots);
...
}
//通過PING,PONG包或者更新包更新紀元當前的最新配置
void clusterUpdateSlotsConfigWith(clusterNode *sender, uint64_t senderConfigEpoch, unsigned char *slots) {
int j;
clusterNode *curmaster, *newmaster = NULL;
/* The dirty slots list is a list of slots for which we lose the ownership
* while having still keys inside. This usually happens after a failover
* or after a manual cluster reconfiguration operated by the admin.
*
* If the update message is not able to demote a master to slave (in this
* case we'll resync with the master updating the whole key space), we
* need to delete all the keys in the slots we lost ownership. */
uint16_t dirty_slots[CLUSTER_SLOTS];
int dirty_slots_count = 0;
/* Here we set curmaster to this node or the node this node
* replicates to if it's a slave. In the for loop we are
* interested to check if slots are taken away from curmaster. */
//如果當前為主，那麼獲取從節點；反之，亦是。
curmaster = nodeIsMaster(myself) ? myself : myself->slaveof;
//如果為自己發出，不處理直接返回
if (sender == myself) {
serverLog(LL_WARNING,"Discarding UPDATE message about myself.");
return;
}
for (j = 0; j < CLUSTER_SLOTS; j++) {
if (bitmapTestBit(slots,j)) {
/* The slot is already bound to the sender of this message. */
//跳過Sender負責的槽
if (server.cluster->slots[j] == sender) continue;
/* The slot is in importing state, it should be modified only
* manually via redis-trib (example: a resharding is in progress
* and the migrating side slot was already closed and is advertising
* a new config. We still want the slot to be closed manually). */
if (server.cluster->importing_slots_from[j]) continue;
/* We rebind the slot to the new node claiming it if:
* 1) The slot was unassigned or the new node claims it with a
* greater configEpoch.
* 2) We are not currently importing the slot. */
if (server.cluster->slots[j] == NULL ||
server.cluster->slots[j]->configEpoch < senderConfigEpoch)
{
/* Was this slot mine, and still contains keys? Mark it as
* a dirty slot. */
if (server.cluster->slots[j] == myself &&
countKeysInSlot(j) &&
sender != myself)
{
dirty_slots[dirty_slots_count] = j;
dirty_slots_count++;
}
if (server.cluster->slots[j] == curmaster)
newmaster = sender;
clusterDelSlot(j);
clusterAddSlot(sender,j);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE|
CLUSTER_TODO_FSYNC_CONFIG);
}
}
}
/* After updating the slots configuration, don't do any actual change
* in the state of the server if a module disabled Redis Cluster
* keys redirections. */
if (server.cluster_module_flags & CLUSTER_MODULE_FLAG_NO_REDIRECTION)
return;
/* If at least one slot was reassigned from a node to another node
* with a greater configEpoch, it is possible that:
* 1) We are a master left without slots. This means that we were
* failed over and we should turn into a replica of the new
* master.
* 2) We are a slave and our master is left without slots. We need
* to replicate to the new slots owner. */
if (newmaster && curmaster->numslots == 0) {
serverLog(LL_WARNING,
"Configuration change detected. Reconfiguring myself "
"as a replica of %.40s", sender->name);
clusterSetMaster(sender);
clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG|
CLUSTER_TODO_UPDATE_STATE|
CLUSTER_TODO_FSYNC_CONFIG);
} else if (dirty_slots_count) {
/* If we are here, we received an update message which removed
* ownership for certain slots we still have keys about, but still
* we are serving some slots, so this master node was not demoted to
* a slave.
*
* In order to maintain a consistent state between keys and slots
* we need to remove all the keys from the slots we lost. */
for (j = 0; j < dirty_slots_count; j++)
delKeysInSlot(dirty_slots[j]);
}
}
這個註釋已經非常明白了。其實就是兩部分，一部分是myself已經實際控制的，這個就不用再處理了，第二個就是myself匯入狀態的槽位，這個需要專門工具來處理。其它就是照單辦事兒即可。在流程中需要進行一下判斷和處理：
最簡單的就是該槽無指定負責節點，直接呼叫函式指派即可；
如果傳送節點的EPOCH更大，則表示傳送節點版本新，需要繼續判斷是否指派衝突或者檢測到了故障。
如果myself在控制這個槽，但訊息中又指定了傳送節點負責，這就是衝突，需要儲存到髒陣列，然後遍歷這個陣列，將其與myself解除關係；
如果myself為從節點，並且槽由其主節點負責，但訊息中顯示該槽為Sender節點，即為故障。這種情況，直接呼叫函式將從設定為主。
在足夠的時間內，每個主節點都會把自己負責的槽位資訊廣播給每個叢集中的節點，那麼，每個節點都知道槽位是如何分配和由誰管理。
三、總結
叢集其實就是一個分散式的計算機小網路，從巨集觀上要處理數量的上限，上限如何確定，是靠基礎的心跳包和通訊數量來設定一個安全的上限值來決定的；換句話說，不能讓服務資料的使用費用超過合理的上限，保證費效比。而從具體上來說，就是要控制不同的計算機協同工作，出現異常時，可以在保證資料安全的前提下，儘量提高呼應速度並轉移相關資料。
實現上面的兩個部分，就需要設計一系列的通訊機制，心跳機制和資料通訊規約，完整的判斷網路線上和異常的情況並根據一系列的操作來協調網路中不同的節點，達到安全穩定的資料服務。
