WAL Storage

In most cases, having pg_wal on the same volume where PGDATA resides is fine. However, having WALs stored in a separate volume has a few benefits

1. Update Cluster with WAL storage

   kubectl apply -f cluster.yaml
   
   apiVersion: postgresql.cnpg.io/v1
   kind: Cluster
   metadata:
     name: echo-postgresql
     namespace: cnpg-system
   spec:
     instances: 3
     storage:
       size: 20Gi
       storageClass: gtf-ack-essd-pl0-wait
     walStorage:
       size: 1Gi
       storageClass: gtf-ack-essd-pl0-wait
   

2. operator will start rollout restart the replica & master automatically. better to have primaryUpdateStrategy: supervised or primaryUpdateStrategy: unsupervised with primaryUpdateMethod: switchover before doing this activity to prevent master pod being terminated.

   zufar.dhiyaullhaq@MacBookPro 5-minor-postgresql-downgrade % k get pvc    
   NAME                             STATUS    VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS            VOLUMEATTRIBUTESCLASS   AGE
   echo-postgresql-13               Bound     d-k1a3qecdmzapcvkw4mol   20Gi       RWO            gtf-ack-essd-pl0-wait   <unset>                 21m
   echo-postgresql-13-wal           Pending                                                      gtf-ack-essd-pl0-wait   <unset>                 2m29s
   echo-postgresql-14               Bound     d-k1a6j280bbsxtsbcnyd6   20Gi       RWO            gtf-ack-essd-pl0-wait   <unset>                 17m
   echo-postgresql-14-wal           Bound     d-k1a19hs0finsu6ev5e9d   1Gi        RWO            gtf-ack-essd-pl0-wait   <unset>                 2m29s
   echo-postgresql-15               Bound     d-k1a4veew50n8oaidjvz2   20Gi       RWO            gtf-ack-essd-pl0-wait   <unset>                 14m
   echo-postgresql-15-wal           Bound     d-k1a7u36tlbwd2cq8v7y7   1Gi        RWO            gtf-ack-essd-pl0-wait   <unset>                 2m29s
   
   zufar.dhiyaullhaq@MacBookPro 5-minor-postgresql-downgrade % k get cluster
   NAME                           AGE     INSTANCES   READY   STATUS                                                     PRIMARY
   echo-postgresql                8d      3           2       Primary instance is being restarted without a switchover   echo-postgresql-13
   
   zufar.dhiyaullhaq@MacBookPro 5-minor-postgresql-downgrade % k get pod
   echo-postgresql-13                         0/1     Terminating   0          21m
   echo-postgresql-14                         1/1     Running       0          2m10s
   echo-postgresql-15                         1/1     Running       0          2m46s
   

Manifests

cluster.yaml

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: echo-postgresql
  namespace: cnpg-system
spec:
  instances: 3
  storage:
    size: 20Gi
    storageClass: gtf-ack-essd-pl0-wait
  walStorage:
    size: 1Gi
    storageClass: gtf-ack-essd-pl0-wait
  primaryUpdateStrategy: unsupervised
  primaryUpdateMethod: switchover

https://cloudnative-pg.io/documentation/1.26/storage/#volume-for-wal