Redis Cluster 的扩展性设计旨在支持水平扩展，使得在数据量增大和负载增加时，可以通过增加节点来分担压力。Redis Cluster 通过哈希槽（hash slots）机制将数据分布在多个节点上，扩展性主要体现在以下几个方面：
- 节点增加：支持动态增加节点，以扩展集群的存储容量和处理能力。
- 重新分片：在新增节点或移除节点时，能够平衡数据分布，重新分配哈希槽。
- 高可用性：通过主从复制及自动故障转移机制，确保集群的高可用性。
以下内容详细描述 Redis Cluster 的扩展性，并结合示例代码进行说明。
1. 节点增加
增加节点是 Redis Cluster 扩展性的基础，通过增加节点，可以将更多的哈希槽分配到新的节点上，从而扩展存储容量和处理能力。
代码示例
c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_NODES 10
#define HASH_SLOTS 16384
typedef struct clusterNode {
char name[40]; /* Node ID */
char ip[16]; /* Node IP */
int port; /* Node Port */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
} clusterNode;
typedef struct cluster {
clusterNode nodes[MAX_NODES];
int node_count;
} cluster;
/* Function to add a new node to the cluster */
void addNode(cluster *cl, const char *name, const char *ip, int port) {
if (cl->node_count < MAX_NODES) {
strcpy(cl->nodes[cl->node_count].name, name);
strcpy(cl->nodes[cl->node_count].ip, ip);
cl->nodes[cl->node_count].port = port;
cl->nodes[cl->node_count].start_slot = -1; // Initial value, to be assigned later
cl->nodes[cl->node_count].end_slot = -1; // Initial value, to be assigned later
cl->node_count++;
} else {
printf("Cluster node limit reached\n");
}
}
/* Example usage */
int main() {
cluster cl = {0};
addNode(&cl, "node1", "192.168.1.1", 6379);
addNode(&cl, "node2", "192.168.1.2", 6379);
for (int i = 0; i < cl.node_count; i++) {
printf("Node %s: %s:%d, Slots: %d-%d\n", cl.nodes[i].name, cl.nodes[i].ip, cl.nodes[i].port, cl.nodes[i].start_slot, cl.nodes[i].end_slot);
}
return 0;
}2. 重新分片
当新增节点时，需要将一些哈希槽重新分配到新的节点上，以实现负载均衡。重新分片的过程包括选择要迁移的槽、将槽的数据从源节点迁移到目标节点，以及更新集群状态。
代码示例
c
#include <stdio.h>
#include <string.h>
typedef struct clusterNode {
char name[40]; /* Node ID */
char ip[16]; /* Node IP */
int port; /* Node Port */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
} clusterNode;
/* Function to determine which slots to migrate */
void selectSlotsToMigrate(clusterNode *src, clusterNode *dst, int num_slots) {
int mid = src->start_slot + (src->end_slot - src->start_slot) / 2;
dst->start_slot = mid + 1;
dst->end_slot = src->end_slot;
src->end_slot = mid;
printf("Migrating slots %d-%d from node %s to node %s\n", dst->start_slot, dst->end_slot, src->name, dst->name);
}
/* Function to migrate slot data */
void migrateSlotData(clusterNode *src, clusterNode *dst, int slot) {
printf("Migrating data for slot %d from node %s to node %s\n", slot, src->name, dst->name);
// In a real implementation, data migration would occur here
}
/* Function to perform resharding */
void reshard(clusterNode *nodes, int node_count) {
for (int i = 0; i < node_count; i++) {
if (nodes[i].start_slot == -1) {
// This is the new node, so we need to reshard
for (int j = 0; j < node_count; j++) {
if (i != j && nodes[j].end_slot > nodes[j].start_slot) {
selectSlotsToMigrate(&nodes[j], &nodes[i], (nodes[j].end_slot - nodes[j].start_slot) / 2);
for (int slot = nodes[i].start_slot; slot <= nodes[i].end_slot; slot++) {
migrateSlotData(&nodes[j], &nodes[i], slot);
}
break;
}
}
break;
}
}
}
/* Example usage */
int main() {
clusterNode nodes[3] = {
{"node1", "192.168.1.1", 6379, 0, 5460},
{"node2", "192.168.1.2", 6379, 5461, 10921},
{"node3", "192.168.1.3", 6379, -1, -1} // New node
};
reshard(nodes, 3);
for (int i = 0; i < 3; i++) {
printf("Node %s: %s:%d, Slots: %d-%d\n", nodes[i].name, nodes[i].ip, nodes[i].port, nodes[i].start_slot, nodes[i].end_slot);
}
return 0;
}3. 高可用性
Redis Cluster 通过主从复制和自动故障转移机制，确保节点故障时的高可用性。在扩展集群时，也需要确保这些机制的正常工作。
代码示例
c
#include <stdio.h>
#include <string.h>
#include <time.h>
#define MAX_NODES 10
#define HEARTBEAT_INTERVAL 1000 // 1 second
#define CLUSTER_NODE_FAIL 0x01
typedef struct clusterNode {
char name[40]; /* Node ID */
char ip[16]; /* Node IP */
int port; /* Node Port */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
int flags; /* Node flags: fail, etc. */
time_t last_heartbeat; /* Last time a heartbeat was received */
struct clusterNode *slaveof; /* Master of this node if it's a slave */
} clusterNode;
typedef struct cluster {
clusterNode nodes[MAX_NODES];
int node_count;
} cluster;
/* Function to add a new node to the cluster */
void addNode(cluster *cl, const char *name, const char *ip, int port) {
if (cl->node_count < MAX_NODES) {
strcpy(cl->nodes[cl->node_count].name, name);
strcpy(cl->nodes[cl->node_count].ip, ip);
cl->nodes[cl->node_count].port = port;
cl->nodes[cl->node_count].start_slot = -1; // Initial value, to be assigned later
cl->nodes[cl->node_count].end_slot = -1; // Initial value, to be assigned later
cl->nodes[cl->node_count].flags = 0;
cl->nodes[cl->node_count].last_heartbeat = time(NULL);
cl->nodes[cl->node_count].slaveof = NULL;
cl->node_count++;
} else {
printf("Cluster node limit reached\n");
}
}
/* Function to send heartbeat message */
void sendHeartbeat(clusterNode *node) {
printf("Sending heartbeat to node %s\n", node->name);
node->last_heartbeat = time(NULL);
}
/* Function to check for node failures based on heartbeat */
void checkHeartbeat(clusterNode *node) {
time_t now = time(NULL);
if (now - node->last_heartbeat > HEARTBEAT_INTERVAL) {
printf("Node %s is not responding\n", node->name);
node->flags |= CLUSTER_NODE_FAIL;
}
}
/* Function to handle failover */
void handleFailover(cluster *cl, clusterNode *failed_node) {
for (int i = 0; i < cl->node_count; i++) {
if (cl->nodes[i].slaveof == failed_node) {
printf("Failover: promoting slave node %s to master\n", cl->nodes[i].name);
cl->nodes[i].flags &= ~CLUSTER_NODE_FAIL;
cl->nodes[i].slaveof = NULL;
}
}
}
/* Example usage */
int main() {
cluster cl = {0};
addNode(&cl, "node1", "192.168.1.1", 6379);