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MySQL InnoDB Cluster - Node lagging behind - election process
Posted by: Carlos Abrantes
Date: August 09, 2023 11:04AM

Hi All,

After deploying InnoDB Cluster with MySQL version 8.0.33 via MySQL Operator i was trying to understand if a node that is lagging could be elected as Primary.

{
"clusterName": "mysql",
"defaultReplicaSet": {
"name": "default",
"primary": "mysql-2.mysql-instances.mysql.svc.cluster.local:3306",
"ssl": "REQUIRED",
"status": "OK",
"statusText": "Cluster is ONLINE and can tolerate up to ONE failure.",
"topology": {
"mysql-0.mysql-instances.mysql.svc.cluster.local:3306": {
"address": "mysql-0.mysql-instances.mysql.svc.cluster.local:3306",
"memberRole": "SECONDARY",
"mode": "R/O",
"readReplicas": {},
"replicationLag": "00:05:34.192010",
"role": "HA",
"status": "ONLINE",
"version": "8.0.33"
},
"mysql-1.mysql-instances.mysql.svc.cluster.local:3306": {
"address": "mysql-1.mysql-instances.mysql.svc.cluster.local:3306",
"memberRole": "SECONDARY",
"mode": "R/O",
"readReplicas": {},
"replicationLag": "applier_queue_applied",
"role": "HA",
"status": "ONLINE",
"version": "8.0.33"
},
"mysql-2.mysql-instances.mysql.svc.cluster.local:3306": {
"address": "mysql-2.mysql-instances.mysql.svc.cluster.local:3306",
"memberRole": "PRIMARY",
"mode": "R/W",
"readReplicas": {},
"replicationLag": "applier_queue_applied",
"role": "HA",
"status": "ONLINE",
"version": "8.0.33"
}
},
"topologyMode": "Single-Primary"
},
"groupInformationSourceMember": "mysql-2.mysql-instances.mysql.svc.cluster.local:3306"
}

The documentation i found don't state that lagging behind will prevent a node to be used as primary, something that can be critical in many use cases, can you please confirm if my understanding is correct?

For me makes since to at least be able to configure the behaviour of a lagging node if should be consider in Primary election or not, basically a threshold after which the node would not be participating in Primary election.

I was not able to find any reference to such behaviour, can you please clarify if it exists, where can i read about it, or if not consider this a Feature Request?

Version:
community-operator:8.0.33-2.0.10
community-server:8.0.33
community-router:8.0.33

apiVersion: v2
appVersion: 8.0.33
description: MySQL InnoDB Cluster Helm Chart for deploying MySQL InnoDB Cluster in Kubernetes
icon: https://labs.mysql.com/common/themes/sakila/favicon.ico
name: mysql-innodbcluster
type: application
version: 2.0.10

Thanks,

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MySQL InnoDB Cluster - Node lagging behind - election process
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August 09, 2023 11:04AM


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