server: expose GetLivenessesFromKV in node liveness interfaces

Expose the GetLivenessesFromKV API we introduced earlier to pkg/sql.
We'll eventually use this to power long running migrations (cockroachdb#56107),
plumbing the liveness instance into the migration manager process.

It should be noted that this will be a relatively meatier form of a
dependency on node liveness from pkg/sql than we have currently. Today
the only uses are in DistSQL planning and in jobs[1]. As it relates to
our multi-tenancy work, the real use of this API will happen only on the
system tenant. System tenants alone have the privilege to set cluster
settings (or at least the version setting specifically), which is what
the migration manager will be wired into.

[1]: cockroachdb#48795

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/liveness/livenesspb"
@@ -28,7 +30,7 @@ var FakeNodeID = func() *base.NodeIDContainer {
 }()
 
 // FakeNodeLiveness allows simulating liveness failures without the full
-// storage.NodeLiveness machinery.
+// liveness.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 liveness.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() (livenesspb.Liveness, bool) {
@@ -75,7 +77,7 @@ func (nl *FakeNodeLiveness) Self() (livenesspb.Liveness, bool) {
 	return *nl.mu.livenessMap[FakeNodeID.Get()], true
 }
 
-// GetLivenesses implements the implicit storage.NodeLiveness interface.
+// GetLivenesses implements the implicit liveness.NodeLiveness interface.
 func (nl *FakeNodeLiveness) GetLivenesses() (out []livenesspb.Liveness) {
 	select {
 	case nl.GetLivenessesCalledCh <- struct{}{}:
@@ -89,6 +91,11 @@ func (nl *FakeNodeLiveness) GetLivenesses() (out []livenesspb.Liveness) {
 	return out
 }
 
+// GetLivenessesFromKV implements the implicit liveness.NodeLiveness interface.
+func (nl *FakeNodeLiveness) GetLivenessesFromKV(context.Context) ([]livenesspb.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/liveness/livenesspb"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/util/errorutil"
@@ -20,6 +22,7 @@ import (
 type Interface interface {
 	Self() (livenesspb.Liveness, bool)
 	GetLivenesses() []livenesspb.Liveness
+	GetLivenessesFromKV(ctx context.Context) ([]livenesspb.Liveness, error)
 	IsLive(roachpb.NodeID) (bool, error)
 }