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This article mainly explains "what is the reason why redis cluster uses 16384 slots". The explanation in the article is simple and clear and easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the reason why redis cluster uses 16384 slots"?

To sum up, there are two main reasons:

Considering the size of the message, the larger the number of slots, the larger the space occupied by the maintenance slot information, which wastes bandwidth and easily leads to network congestion.

To join a node to a cluster in redis cluster, you need to execute cluster meet ip:port to complete the node handshake, and then the nodes can exchange information through regular ping-pong. The header structure is as follows:

# define CLUSTER_SLOTS 16384

Typedef struct {

Char sig [4]; / * Signature "RCmb" (Redis Cluster message bus). , /

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 * /

Uint16_t count; / * Only used for some kind of messages. , /

Uint64_t currentEpoch; / * The epoch accordingly to the sending node. , /

Uint64_t configEpoch; / * The config epoch if it's a master, or the last

Epoch advertised by its master if it is a

Slave. , /

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]

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

Unsigned char myslots [cluster _ SLOTS/8]; maintains the bitmap of the slot information held by the current node. Each bit represents a slot, and a corresponding bit of 1 indicates that the slot belongs to the current node. Because of # define CLUSTER_SLOTS 16384, the space occupied by myslots is: 16384/8/1024=2kb, but if # define CLUSTER_SLOTS is 65536, it takes up 8kb.

And the message body will also carry the information of other nodes for exchange. This "other node information" is about 1 / 10 of the number of cluster nodes and carries at least 3 nodes' information. Therefore, the more nodes in the cluster, the more space the message content takes up.

It is generally impossible for a redis cluster to have more than 1000 master nodes.

The more nodes, the larger the exchange message; on the other hand, because the node slot information is maintained through bitmap, bitmap will be compressed in the process of transmission. If the slot is smaller and there are fewer nodes, the filling ratio slots/N (N represents the number of nodes) of bitmap is smaller, and the corresponding compression ratio is higher. On the contrary, if there are few slots, the compression ratio is very low.

Therefore, taking it into consideration, the author thinks that 16384 slots will actually be enough.

Thank you for your reading, the above is the content of "what is the reason for the use of 16384 slots in redis cluster". After the study of this article, I believe you have a deeper understanding of the reason why redis cluster happens to use 16384 slots, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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