server: expose GetLivenessesFromKV in node liveness interfaces

To flesh out the migrations infrastructure (in future commits), we'll
need a handle on all the nodes present in the system. Now that we always
create a liveness record on start up (cockroachdb#53805), we can simply fetch all
liveness records from KV. We add a helper to do so.

It's a bit unfortunate that we're further adding on to the NodeLiveness
API without changing the caching structure, but the methods fetching
records from KV is the world we're hoping to move towards going forward.

This does mean that we're introducing a direct dependency on
NodeLiveness in the sql layer, and there's improvements to be made here
around interfaces delineating between "system tenant only" sql code and
everything else. Only system tenants have the privilege to set cluster
settings (or at least the version setting specifically), which is what
this API will look to power.

Release note: None

pkg/jobs/helpers.go

@@ -11,6 +11,8 @@
 package jobs
 
 import (
+	"context"
+
 	"github.com/cockroachdb/cockroach/pkg/base"
 	"github.com/cockroachdb/cockroach/pkg/jobs/jobspb"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvserverpb"
@@ -28,7 +30,7 @@ var FakeNodeID = func() *base.NodeIDContainer {
 }()
 
 // FakeNodeLiveness allows simulating liveness failures without the full
-// storage.NodeLiveness machinery.
+// kvserver.NodeLiveness machinery.
 type FakeNodeLiveness struct {
 	mu struct {
 		syncutil.Mutex
@@ -62,7 +64,7 @@ func NewFakeNodeLiveness(nodeCount int) *FakeNodeLiveness {
 // ModuleTestingKnobs implements base.ModuleTestingKnobs.
 func (*FakeNodeLiveness) ModuleTestingKnobs() {}
 
-// Self implements the implicit storage.NodeLiveness interface. It uses NodeID
+// Self implements the implicit kvserver.NodeLiveness interface. It uses NodeID
 // as the node ID. On every call, a nonblocking send is performed over nl.ch to
 // allow tests to execute a callback.
 func (nl *FakeNodeLiveness) Self() (kvserverpb.Liveness, bool) {
@@ -75,7 +77,7 @@ func (nl *FakeNodeLiveness) Self() (kvserverpb.Liveness, bool) {
 	return *nl.mu.livenessMap[FakeNodeID.Get()], true
 }
 
-// GetLivenesses implements the implicit storage.NodeLiveness interface.
+// GetLivenesses implements the implicit kvserver.NodeLiveness interface.
 func (nl *FakeNodeLiveness) GetLivenesses() (out []kvserverpb.Liveness) {
 	select {
 	case nl.GetLivenessesCalledCh <- struct{}{}:
@@ -89,6 +91,11 @@ func (nl *FakeNodeLiveness) GetLivenesses() (out []kvserverpb.Liveness) {
 	return out
 }
 
+// GetLivenessesFromKV implements the implicit kvserver.NodeLiveness interface.
+func (nl *FakeNodeLiveness) GetLivenessesFromKV(context.Context) ([]kvserverpb.Liveness, error) {
+	return nil, errors.New("FakeNodeLiveness.GetLivenessesFromKV is unimplemented")
+}
+
 // IsLive is unimplemented.
 func (nl *FakeNodeLiveness) IsLive(roachpb.NodeID) (bool, error) {
 	return false, errors.New("FakeNodeLiveness.IsLive is unimplemented")

pkg/sql/optionalnodeliveness/node_liveness.go

@@ -11,6 +11,8 @@
 package optionalnodeliveness
 
 import (
+	"context"
+
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvserverpb"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/util/errorutil"
@@ -20,6 +22,7 @@ import (
 type Interface interface {
 	Self() (kvserverpb.Liveness, bool)
 	GetLivenesses() []kvserverpb.Liveness
+	GetLivenessesFromKV(ctx context.Context) ([]kvserverpb.Liveness, error)
 	IsLive(roachpb.NodeID) (bool, error)
 }