Add shm_volume option (#427)

Add possibility to mount a tmpfs volume to /dev/shm to avoid issues like
[this](https://github.com/docker-library/postgres/issues/416). To achieve that
two new options were introduced:

* `enableShmVolume` to PostgreSQL manifest, to specify whether or not mount
this volume per database cluster

* `enable_shm_volume` to operator configuration, to specify whether or not mount
per operator.

The first one, `enableShmVolume` takes precedence to allow us to be more flexible.

docs/reference/cluster_manifest.md

@@ -97,6 +97,18 @@ Those are parameters grouped directly under  the `spec` key in the manifest.
    is taken from the `pod_priority_class_name` operator parameter, if not set
    then the default priority class is taken. The priority class itself must be defined in advance.
 
+* **enableShmVolume**
+  Start a database pod without limitations on shm memory. By default docker
+  limit `/dev/shm` to `64M` (see e.g. the [docker
+  issue](https://github.com/docker-library/postgres/issues/416), which could be
+  not enough if PostgreSQL uses parallel workers heavily. If this option is
+  present and value is `true`, to the target database pod will be mounted a new
+  tmpfs volume to remove this limitation. If it's not present, the decision
+  about mounting a volume will be made based on operator configuration
+  (`enable_shm_volume`, which is `true` by default). It it's present and value
+  is `false`, then no volume will be mounted no matter how operator was
+  configured (so you can override the operator configuration).
+
 ## Postgres parameters
 
 Those parameters are grouped under the `postgresql` top-level key.
@@ -112,6 +124,7 @@ Those parameters are grouped under the `postgresql` top-level key.
   cluster. Optional (Spilo automatically sets reasonable defaults for
   parameters like work_mem or max_connections).
 
+
 ## Patroni parameters
 
 Those parameters are grouped under the `patroni` top-level key. See the [patroni

docs/reference/operator_parameters.md

@@ -224,6 +224,14 @@ CRD-based configuration.
 * **set_memory_request_to_limit**
   Set `memory_request` to `memory_limit` for all Postgres clusters (the default value is also increased). This prevents certain cases of memory overcommitment at the cost of overprovisioning memory and potential scheduling problems for containers with high memory limits due to the lack of memory on Kubernetes cluster nodes. This affects all containers (Postgres, Scalyr sidecar, and other sidecars). The default is `false`.
 
+* **enable_shm_volume**
+  Instruct operator to start any new database pod without limitations on shm
+  memory. If this option is enabled, to the target database pod will be mounted
+  a new tmpfs volume to remove shm memory limitation (see e.g. the [docker
+  issue](https://github.com/docker-library/postgres/issues/416)). This option
+  is global for an operator object, and can be overwritten by `enableShmVolume`
+  parameter from Postgres manifest. The default is `true`
+
 ## Operator timeouts
 
 This set of parameters define various timeouts related to some operator

manifests/complete-postgres-manifest.yaml

@@ -19,6 +19,7 @@ spec:
   databases:
     foo: zalando
 #Expert section
+  enableShmVolume: true
   postgresql:
     version: "10"
     parameters:

pkg/apis/acid.zalan.do/v1/postgresql_type.go

@@ -51,6 +51,7 @@ type PostgresSpec struct {
 	Tolerations          []v1.Toleration      `json:"tolerations,omitempty"`
 	Sidecars             []Sidecar            `json:"sidecars,omitempty"`
 	PodPriorityClassName string               `json:"pod_priority_class_name,omitempty"`
+	ShmVolume            *bool                `json:"enableShmVolume,omitempty"`
 }
 
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object

pkg/apis/acid.zalan.do/v1/util_test.go

@@ -499,7 +499,7 @@ func TestMarshal(t *testing.T) {
 			t.Errorf("Marshal error: %v", err)
 		}
 		if !bytes.Equal(m, tt.marshal) {
-			t.Errorf("Marshal Postgresql expected: %q, got: %q", string(tt.marshal), string(m))
+			t.Errorf("Marshal Postgresql \nexpected: %q, \ngot:      %q", string(tt.marshal), string(m))
 		}
 	}
 }
@@ -507,11 +507,11 @@ func TestMarshal(t *testing.T) {
 func TestPostgresMeta(t *testing.T) {
 	for _, tt := range unmarshalCluster {
 		if a := tt.out.GetObjectKind(); a != &tt.out.TypeMeta {
-			t.Errorf("GetObjectKindMeta expected: %v, got: %v", tt.out.TypeMeta, a)
+			t.Errorf("GetObjectKindMeta \nexpected: %v, \ngot:       %v", tt.out.TypeMeta, a)
 		}
 
 		if a := tt.out.GetObjectMeta(); reflect.DeepEqual(a, tt.out.ObjectMeta) {
-			t.Errorf("GetObjectMeta expected: %v, got: %v", tt.out.ObjectMeta, a)
+			t.Errorf("GetObjectMeta \nexpected: %v, \ngot:       %v", tt.out.ObjectMeta, a)
 		}
 	}
 }

pkg/cluster/k8sres.go

@@ -18,6 +18,7 @@ import (
 	acidv1 "github.com/zalando-incubator/postgres-operator/pkg/apis/acid.zalan.do/v1"
 	"github.com/zalando-incubator/postgres-operator/pkg/spec"
 	"github.com/zalando-incubator/postgres-operator/pkg/util"
+	"github.com/zalando-incubator/postgres-operator/pkg/util/config"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/constants"
 	"k8s.io/apimachinery/pkg/labels"
 )
@@ -396,6 +397,16 @@ func generateSidecarContainers(sidecars []acidv1.Sidecar,
 	return nil, nil
 }
 
+// Check whether or not we're requested to mount an shm volume,
+// taking into account that PostgreSQL manifest has precedence.
+func mountShmVolumeNeeded(opConfig config.Config, pgSpec *acidv1.PostgresSpec) bool {
+	if pgSpec.ShmVolume != nil {
+		return *pgSpec.ShmVolume
+	}
+
+	return opConfig.ShmVolume
+}
+
 func generatePodTemplate(
 	namespace string,
 	labels labels.Set,
@@ -407,6 +418,7 @@ func generatePodTemplate(
 	podServiceAccountName string,
 	kubeIAMRole string,
 	priorityClassName string,
+	shmVolume bool,
 ) (*v1.PodTemplateSpec, error) {
 
 	terminateGracePeriodSeconds := terminateGracePeriod
@@ -420,6 +432,10 @@ func generatePodTemplate(
 		Tolerations:                   *tolerationsSpec,
 	}
 
+	if shmVolume {
+		addShmVolume(&podSpec)
+	}
+
 	if nodeAffinity != nil {
 		podSpec.Affinity = nodeAffinity
 	}
@@ -733,7 +749,12 @@ func (c *Cluster) generateStatefulSet(spec *acidv1.PostgresSpec) (*v1beta1.State
 	volumeMounts := generateVolumeMounts()
 
 	// generate the spilo container
-	spiloContainer := generateSpiloContainer(c.containerName(), &effectiveDockerImage, resourceRequirements, spiloEnvVars, volumeMounts)
+	spiloContainer := generateSpiloContainer(c.containerName(),
+		&effectiveDockerImage,
+		resourceRequirements,
+		spiloEnvVars,
+		volumeMounts,
+	)
 
 	// resolve conflicts between operator-global and per-cluster sidecards
 	sideCars := c.mergeSidecars(spec.Sidecars)
@@ -775,7 +796,8 @@ func (c *Cluster) generateStatefulSet(spec *acidv1.PostgresSpec) (*v1beta1.State
 		int64(c.OpConfig.PodTerminateGracePeriod.Seconds()),
 		c.OpConfig.PodServiceAccountName,
 		c.OpConfig.KubeIAMRole,
-		effectivePodPriorityClassName); err != nil {
+		effectivePodPriorityClassName,
+		mountShmVolumeNeeded(c.OpConfig, spec)); err != nil {
 		return nil, fmt.Errorf("could not generate pod template: %v", err)
 	}
 
@@ -882,6 +904,32 @@ func (c *Cluster) getNumberOfInstances(spec *acidv1.PostgresSpec) int32 {
 	return newcur
 }
 
+// To avoid issues with limited /dev/shm inside docker environment, when
+// PostgreSQL can't allocate enough of dsa segments from it, we can
+// mount an extra memory volume
+//
+// see https://docs.okd.io/latest/dev_guide/shared_memory.html
+func addShmVolume(podSpec *v1.PodSpec) {
+	volumes := append(podSpec.Volumes, v1.Volume{
+		Name: constants.ShmVolumeName,
+		VolumeSource: v1.VolumeSource{
+			EmptyDir: &v1.EmptyDirVolumeSource{
+				Medium: "Memory",
+			},
+		},
+	})
+
+	pgIdx := constants.PostgresContainerIdx
+	mounts := append(podSpec.Containers[pgIdx].VolumeMounts,
+		v1.VolumeMount{
+			Name:      constants.ShmVolumeName,
+			MountPath: constants.ShmVolumePath,
+		})
+
+	podSpec.Containers[0].VolumeMounts = mounts
+	podSpec.Volumes = volumes
+}
+
 func generatePersistentVolumeClaimTemplate(volumeSize, volumeStorageClass string) (*v1.PersistentVolumeClaim, error) {
 
 	var storageClassName *string

pkg/cluster/k8sres_test.go

@@ -1,8 +1,11 @@
 package cluster
 
 import (
+	"k8s.io/api/core/v1"
+
 	acidv1 "github.com/zalando-incubator/postgres-operator/pkg/apis/acid.zalan.do/v1"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/config"
+	"github.com/zalando-incubator/postgres-operator/pkg/util/constants"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/k8sutil"
 	"testing"
 )
@@ -75,3 +78,54 @@ func TestCreateLoadBalancerLogic(t *testing.T) {
 		}
 	}
 }
+
+func TestShmVolume(t *testing.T) {
+	testName := "TestShmVolume"
+	tests := []struct {
+		subTest string
+		podSpec *v1.PodSpec
+		shmPos  int
+	}{
+		{
+			subTest: "empty PodSpec",
+			podSpec: &v1.PodSpec{
+				Volumes: []v1.Volume{},
+				Containers: []v1.Container{
+					v1.Container{
+						VolumeMounts: []v1.VolumeMount{},
+					},
+				},
+			},
+			shmPos: 0,
+		},
+		{
+			subTest: "non empty PodSpec",
+			podSpec: &v1.PodSpec{
+				Volumes: []v1.Volume{v1.Volume{}},
+				Containers: []v1.Container{
+					v1.Container{
+						VolumeMounts: []v1.VolumeMount{
+							v1.VolumeMount{},
+						},
+					},
+				},
+			},
+			shmPos: 1,
+		},
+	}
+	for _, tt := range tests {
+		addShmVolume(tt.podSpec)
+
+		volumeName := tt.podSpec.Volumes[tt.shmPos].Name
+		volumeMountName := tt.podSpec.Containers[0].VolumeMounts[tt.shmPos].Name
+
+		if volumeName != constants.ShmVolumeName {
+			t.Errorf("%s %s: Expected volume %s was not created, have %s instead",
+				testName, tt.subTest, constants.ShmVolumeName, volumeName)
+		}
+		if volumeMountName != constants.ShmVolumeName {
+			t.Errorf("%s %s: Expected mount %s was not created, have %s instead",
+				testName, tt.subTest, constants.ShmVolumeName, volumeMountName)
+		}
+	}
+}

pkg/util/config/config.go

@@ -38,6 +38,7 @@ type Resources struct {
 	NodeReadinessLabel      map[string]string `name:"node_readiness_label" default:""`
 	MaxInstances            int32             `name:"max_instances" default:"-1"`
 	MinInstances            int32             `name:"min_instances" default:"-1"`
+	ShmVolume               bool              `name:"enable_shm_volume" default:"true"`
 }
 
 // Auth describes authentication specific configuration parameters

pkg/util/constants/kubernetes.go

@@ -5,6 +5,7 @@ import "time"
 // General kubernetes-related constants
 const (
 	PostgresContainerName       = "postgres"
+	PostgresContainerIdx        = 0
 	K8sAPIPath                  = "/apis"
 	StatefulsetDeletionInterval = 1 * time.Second
 	StatefulsetDeletionTimeout  = 30 * time.Second

pkg/util/constants/postgresql.go

@@ -10,4 +10,7 @@ const (
 
 	PostgresConnectRetryTimeout = 2 * time.Minute
 	PostgresConnectTimeout      = 15 * time.Second
+
+	ShmVolumeName = "dshm"
+	ShmVolumePath = "/dev/shm"
 )