Redis Cluster 的重新分片（resharding）是指在集群中将哈希槽从一个节点迁移到另一个节点，以实现负载均衡或其他维护操作。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、更新集群状态等步骤。
重新分片的关键步骤
- 选择要迁移的槽：决定哪些槽需要从源节点迁移到目标节点。
- 迁移槽的数据：将槽的数据从源节点迁移到目标节点。
- 更新集群状态：更新集群元数据，使其他节点知道槽的位置变化。
详细实现步骤和代码示例
1. 选择要迁移的槽
首先，我们需要确定哪些槽需要迁移。这可以根据负载情况、节点容量等条件来决定。
c
#include <stdio.h>
#define HASH_SLOTS 16384
typedef struct clusterNode {
char name[40]; /* Node ID */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
} clusterNode;
/* Function to determine which slots to migrate */
void selectSlotsToMigrate(clusterNode *src, int *slots_to_migrate, int num_slots) {
int index = 0;
for (int i = src->start_slot; i <= src->end_slot && index < num_slots; i++) {
slots_to_migrate[index++] = i;
}
}
/* Example usage */
int main() {
clusterNode src = {"source_node", 0, 5460};
int slots_to_migrate[10];
selectSlotsToMigrate(&src, slots_to_migrate, 10);
printf("Slots to migrate: ");
for (int i = 0; i < 10; i++) {
printf("%d ", slots_to_migrate[i]);
}
printf("\n");
return 0;
}2. 迁移槽的数据
迁移槽的数据涉及将槽中的键值对从源节点发送到目标节点。这需要通过网络通信来实现。
c
#include <stdio.h>
typedef struct clusterNode {
char name[40]; /* Node ID */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
} clusterNode;
/* Function to migrate a single slot's 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, here you would send the data over the network from src to dst.
}
/* Example usage */
int main() {
clusterNode src = {"source_node", 0, 5460};
clusterNode dst = {"destination_node", 5461, 10921};
int slots_to_migrate[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
for (int i = 0; i < 10; i++) {
migrateSlotData(&src, &dst, slots_to_migrate[i]);
}
return 0;
}3. 更新集群状态
一旦数据迁移完成，需要更新集群的元数据，使集群内的所有节点都知道槽的新位置。
c
#include <stdio.h>
typedef struct clusterNode {
char name[40]; /* Node ID */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
} clusterNode;
/* Function to update cluster state */
void updateClusterState(clusterNode *src, clusterNode *dst, int *slots_to_migrate, int num_slots) {
for (int i = 0; i < num_slots; i++) {
int slot = slots_to_migrate[i];
if (slot >= src->start_slot && slot <= src->end_slot) {
printf("Updating cluster state for slot %d: from node %s to node %s\n", slot, src->name, dst->name);
// Update the slot range in the source and destination nodes
if (slot == src->start_slot) {
src->start_slot++;
} else if (slot == src->end_slot) {
src->end_slot--;
}
// Update destination node's slot range
if (dst->start_slot == -1 && dst->end_slot == -1) {
dst->start_slot = slot;
dst->end_slot = slot;
} else {
if (slot < dst->start_slot) {
dst->start_slot = slot;
}
if (slot > dst->end_slot) {
dst->end_slot = slot;
}
}
}
}
}
/* Example usage */
int main() {
clusterNode src = {"source_node", 0, 5460};
clusterNode dst = {"destination_node", 5461, 10921};
int slots_to_migrate[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
updateClusterState(&src, &dst, slots_to_migrate, 10);
printf("Source node %s: slots %d - %d\n", src.name, src.start_slot, src.end_slot);
printf("Destination node %s: slots %d - %d\n", dst.name, dst.start_slot, dst.end_slot);
return 0;
}综合示例
以下是一个完整的示例，展示了如何选择要迁移的槽、迁移槽的数据以及更新集群状态。
c
#include <stdio.h>
#define HASH_SLOTS 16384
typedef struct clusterNode {
char name[40]; /* Node ID */
int start_slot; /* Start hash slot */
int end_slot; /* End hash slot */
} clusterNode;
/* Function to determine which slots to migrate */
void selectSlotsToMigrate(clusterNode *src, int *slots_to_migrate, int num_slots) {
int index = 0;
for (int i = src->start_slot; i <= src->end_slot && index < num_slots; i++) {
slots_to_migrate[index++] = i;
}
}
/* Function to migrate a single slot's 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, here you would send the data over the network from src to dst.
}
/* Function to update cluster state */
void updateClusterState(clusterNode *src, clusterNode *dst, int *slots_to_migrate, int num_slots) {
for (int i = 0; i < num_slots; i++) {
int slot = slots_to_migrate[i];
if (slot >= src->start_slot && slot <= src->end_slot) {
printf("Updating cluster state for slot %d: from node %s to node %s\n", slot, src->name, dst->name);
// Update the slot range in the source and destination nodes
if (slot == src->start_slot) {
src->start_slot++;
} else if (slot == src->end_slot) {
src->end_slot--;
}
// Update destination node's slot range
if (dst->start_slot == -1 && dst->end_slot == -1) {
dst->start_slot = slot;
dst->end_slot = slot;
} else {
if (slot < dst->start_slot) {
dst->start_slot = slot;
}
if (slot > dst->end_slot) {
dst->end_slot = slot;
}
}
}
}
}
/* Example usage */
int main() {
clusterNode src = {"source_node", 0, 5460};
clusterNode dst = {"destination_node", 5461, 10921};
int slots_to_migrate[10];
selectSlotsToMigrate(&src, slots_to_migrate, 10);
for (int i = 0; i < 10; i++) {
migrateSlotData(&src, &dst, slots_to_migrate[i]);
}
updateClusterState(&src, &dst, slots_to_migrate, 10);
printf("Source node %s: slots %d - %d\n", src.name, src.start_slot, src.end_slot);
printf("Destination node %s: slots %d - %d\n", dst.name, dst.start_slot, dst.end_slot);
return 0;
}这个完整的示例展示了 Redis Cluster 重新分片的基本流程，包括选择迁移的槽、迁移槽的数据以及更新集群状态。在实际的 Redis 实现中，这些操作会涉及网络通信和更多的错误处理逻辑，以确保数据的一致性和可靠性。