When gitlab was recently deployed on k8s, the underlying storage used CEPH. As a result, PostgreSQL encountered the following error:

$ kubectl -n gitlab logs postgresql-76d969dd56-m79wm
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.utf8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

initdb: error: directory "/var/lib/postgresql/data" exists but is not empty
It contains a lost+found directory, perhaps due to it being a mount point.
Using a mount point directly as the data directory is not recommended.
Create a subdirectory under the mount point.

PostgreSQL yaml file:

# pv
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgresql-ceph-pvc
  namespace: gitlab
spec:
  storageClassName: ceph-leffss
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
 
---
apiVersion: v1
kind: Service
metadata:
  name: postgresql
  namespace: gitlab
  labels:
    app: gitlab
    tier: postgreSQL
spec:
  ports:
    - port: 5432
  selector:
    app: gitlab
    tier: postgreSQL

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgresql
  namespace: gitlab
  labels:
    app: gitlab
    tier: postgreSQL
spec:
  replicas: 1
  selector:
    matchLabels:
      app: gitlab
      tier: postgreSQL
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: gitlab
        tier: postgreSQL
    spec:
      #nodeSelector:
      #  gee/disk: "500g"
      containers:
        - image: hub.leffss.com/library/postgres:12.6-alpine
        #- image: harbor.boge.com/library/postgres:12.6-alpine
          name: postgresql
          env:
            - name: POSTGRES_USER
              value: gitlab
            - name: POSTGRES_DB
              value: gitlabhq_production
            - name: POSTGRES_PASSWORD
              value: bogeusepg
            - name: TZ
              value: Asia/Shanghai
          ports:
            - containerPort: 5432
              name: postgresql
          livenessProbe:
            exec:
              command:
              - sh
              - -c
              - exec pg_isready -U gitlab -h 127.0.0.1 -p 5432 -d gitlabhq_production
            initialDelaySeconds: 110
            timeoutSeconds: 5
            failureThreshold: 6
          readinessProbe:
            exec:
              command:
              - sh
              - -c
              - exec pg_isready -U gitlab -h 127.0.0.1 -p 5432 -d gitlabhq_production
            initialDelaySeconds: 20
            timeoutSeconds: 3
            periodSeconds: 5
#          resources:
#            requests:
#              cpu: 100m
#              memory: 512Mi
#            limits:
#              cpu: "1"
#              memory: 1Gi
          volumeMounts:
            - name: postgresql
              mountPath: /var/lib/postgresql/data
      volumes:
        - name: postgresql
          persistentVolumeClaim:
            claimName: postgresql-ceph-pvc

Solution: add a subpath parameter in volumemounts

  volumeMounts:
    - name: postgresql
      mountPath: /var/lib/postgresql/data
      subPath: data