Redis cluster re fragmentation and ask command

1. redis Cluster re fragmentation and ASK command
   1. Slicing principle
   2. ASK command
   3. ASK Command and MOVED Distinction of command
   4. summary
   5. ️ Thank you for your

redis Cluster re fragmentation and ASK command

redis Re slicing is to allocate time slot bits from one node to another , It also transmits the key value pair where the time slot is located .

Slicing principle

redis The fragmentation of the cluster is determined by redis-trib management .

First , Send... To the target node import command , When the target node is ready to import the key belonging to this slot - Value to time , send out migrating command , The source node is ready to store the key of this slot - The value pair obtains the key to be transferred from the source node , send out migrate Command to transfer the key , And after knowing that all keys have been transferred ,redis-trib Send... To any node in the cluster node Command to throw the information of the target node

import The command sets the target node's clusterState Structural importing_slots_from The value of the element of the corresponding slot in the array is changed to the value of the source destination clusterNode structure , and migrating command

ASK command

During re slicing , When the client sends a command related to the database key , The key is being migrated . here , The source node first checks to see if there is..., in its database , If you return to a non-existent source node , Then return to ASK Command error message , Guide the client to the target node , Then send the last command again . ASK Commands are also hidden in cluster environments . If the client receives ASK Error and move it to the node in the slot being imported , Then the client must send ASKING Command to resend the command for a specific key operation . If you don't send , The node will be rejected , And back to MOVED error . ASKING Command opens the of the client sending the command REDIS_ASKING. this id It's a one-off id, Running the command once will delete the id.

ASK Command and MOVED Distinction of command

ASK Command and MOVED The difference between orders is ,MOVED The error is transferred from the node responsible for the slot to another node , When the command of the slot is encountered in the future, send the command request directly to the node in charge of the slot . ASK The error is the temporary scheme used during the migration of two nodes , In the event of a ASK After error , The command request of the slot is still sent to the node currently responsible for the slot .

summary

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