A core dump can be generated for a single pod, or for all pods in the SingleStore DB cluster.

Enable Core Dumps

Core dumps can be enabled on individual pods, or across all pods.

Individual Pods

1. List all pods in the cluster.

   kubectl get pods -l app.kubernetes.io/name=memsql-cluster,app.kubernetes.io/instance=<cluster-name>
   

2. Confirm that a core dump will be produced upon crash.

   kubectl exec <pod-name> -c node -- memsqlctl query --sql "SELECT @@core_file"
   ****
   +-------------+
   | @@core_file |
   +-------------+
   | 1           |
   +-------------+
   

   The default value for @@core_file is 1, which indicates that creating a core dump on crash is enabled. If this value is 0, creating a core dump on crash is disabled. To enable it, run the following command.

   kubectl exec <pod-name> -c node -- memsqlctl -y update-config --key core_file --value ON
   

   Restart the node for this change to take effect.

   kubectl exec <pod-name> -c node -- memsqlctl -y restart-node
   

3. Configure the core dump to be either partial or full. By default, a partial core dump is created. Refer to the core_file_mode engine variable for more information on partial and full core dumps.

   Run the following command to check the current value.

   kubectl exec node-memsql-cluster-master-0 -c node -- memsqlctl query --sql "SELECT @@core_file_mode"
   ****
   +------------------+
   | @@core_file_mode |
   +------------------+
   | PARTIAL          |
   +------------------+
   

   Run the following command to change this value.

   For a partial core dump:

   kubectl exec <pod-namne> -c node -- memsqlctl -y update-config --key core_file_mode --value PARTIAL
   

   For a full core dump:

   kubectl exec <pod-name> -c node -- memsqlctl -y update-config --key core_file_mode --value FULL
   

   Restart the node for this change to take effect.

   kubectl exec <pod-name> -c node -- memsqlctl -y restart-node
   

Across all Pods

1. To make the above core dump changes across all pods, add the following subsection to the memsql-cluster.yaml file’s spec section. Refer to the core_file_mode engine variable for more information on partial and full core dumps.

   globalVariables:
     core_file: "ON"
     core_file_mode: "FULL"    # or "PARTIAL", depending on your goal
   

2. Apply these values to enable core dumps on all pods.

   kubectl apply -f memsql-cluster.yaml
   

Generate Core Dumps

1. Display the pods and the nodes they are on. Note that the following output may vary.

   kubectl get pods -l app.kubernetes.io/name=memsql-cluster,app.kubernetes.io/instance=<cluster-name> -o wide
   ****
   NAME                               READY   STATUS    RESTARTS   AGE     IP          NODE                                   NOMINATED NODE   READINESS GATES
   node-memsql-cluster-aggregator-0   2/2     Running   0          4h13m   10.4.0.20   gke-foo-1-default-pool-ed7b330b-2q1r   <none>           <none>
   node-memsql-cluster-leaf-ag1-0     2/2     Running   0          4h13m   10.4.3.10   gke-foo-1-default-pool-ed7b330b-w12w   <none>           <none>
   node-memsql-cluster-leaf-ag2-0     2/2     Running   0          4h13m   10.4.1.8    gke-foo-1-default-pool-ed7b330b-64r5   <none>           <none>
   node-memsql-cluster-master-0       2/2     Running   0          4h13m   10.4.4.24   gke-foo-1-default-pool-ed7b330b-klnz   <none>           <none>
   

Using an SSH Connection

Note: These steps affect all core dump generation for processes on the nodes, not just SingleStore DB containers on the nodes.

1. For each node that contains the pods you want to generate a core dump for, SSH into the node and run the following command.

   echo "core.%d" > /proc/sys/kernel/core_pattern
   

Using a DaemonSet

1. Create a memsql-coredump.yaml file using the following template.

   apiVersion: apps/v1
   kind: DaemonSet
   metadata:
     name: memsql-sysreq
     labels:
       "app.kubernetes.io/name": "memsql-sysreq"
   spec:
     selector:
       matchLabels:
         "app.kubernetes.io/name": "memsql-sysreq"
     updateStrategy:
       type: RollingUpdate
     template:
       metadata:
         labels:
           "app.kubernetes.io/name": "memsql-sysreq"
       spec:
         hostPID: true
         volumes:
         - name: sys
           hostPath:
             path: /sys
         affinity:
           podAffinity:
             requiredDuringSchedulingIgnoredDuringExecution:
             - labelSelector:
                 matchLabels:
                   app.kubernetes.io/instance: CLUSTER_NAME
                   app.kubernetes.io/name: memsql-cluster
                      
                   #Add this line if you only want to generate core for Master Aggregator
                   #app.kubernetes.io/component: master
                   #change master to aggregator or leaf if you only want to generate core
                   #for child aggregator or for leaf
      
                   #Add this line if you only want to generate core for one particular pod, 
                   #substitute POD_NAME with the name of the pod
                   #statefulset.kubernetes.io/pod-name: POD_NAME
               topologyKey: kubernetes.io/hostname
      
         initContainers:
         - name: sysreq
           image: busybox
           securityContext:
             privileged: true
           volumeMounts:
           - name: sys
             mountPath: /rootfs/sys
           command:
           - "/bin/sh"
           - "-c"
           - |
             echo “core.%d” > /proc/sys/kernel/core_pattern
      
         containers:
         - name: pause
           image: gcr.io/google_containers/pause
   

2. Edit the following placeholders in this file:

   • Change CLUSTER_NAME to the SingleStore DB cluster name.
   • To generate the core dump in a specific pod, change POD_NAME to the desired pod.

3. Enable the core dump(s) at the Kubernetes host level. Note that you must have cluster admin privileges to run this command.

   kubectl apply -f memsql-coredump.yaml
   

Core Dump Location

Given the above configuration, and should the SingleStore DB server crash, a core dump will be written to /var/lib/memsql/instance/data/core.memsqld in the restarted pod.

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