kvserver: propose empty entry on unquiescence

During Raft unquiescence, an empty command is proposed to wake the Raft
leader. However, this empty command was encoded as a regular Raft
command with its own command ID and an empty payload. Meanwhile, the
downstream Raft application expects such noop commands to be entirely
empty (i.e. the entire Raft entry is empty), rather than an entry with
an empty payload. This caused it to interpret the command as having a
`ProposerLeaseSequence` of 0 and return a `NotLeaseHolderError` rather
than considering it a noop. Construction and processing of this error
has a non-negligible cost when unquiescing large numbers of ranges.

This patch instead proposes an empty entry on unquiescence.

Epic: none
Release note: None

pkg/kv/kvserver/kvserverbase/forced_error.go

@@ -95,11 +95,11 @@ func CheckForcedErr(
 		requestedLease = *raftCmd.ReplicatedEvalResult.State.Lease
 	}
 	if idKey == "" {
-		// This is an empty Raft command (which is sent by Raft after elections
-		// to trigger reproposals or during concurrent configuration changes).
-		// Nothing to do here except making sure that the corresponding batch
-		// (which is bogus) doesn't get executed (for it is empty and so
-		// properties like key range are undefined).
+		// This is an empty Raft command (which is sent by Raft after elections to
+		// trigger reproposals, during concurrent configuration changes, or to
+		// unquiesce the Raft group). Nothing to do here except making sure that the
+		// corresponding batch (which is bogus) doesn't get executed (for it is
+		// empty and so properties like key range are undefined).
 		return ForcedErrResult{
 			LeaseIndex:  leaseIndex,
 			Rejection:   ProposalRejectionPermanent,

pkg/kv/kvserver/replica_raft_quiesce.go

@@ -16,7 +16,6 @@ import (
 
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvserverpb"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/liveness/livenesspb"
-	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/raftlog"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
@@ -88,8 +87,7 @@ func (r *Replica) maybeUnquiesceAndWakeLeaderLocked() bool {
 	r.store.unquiescedReplicas.Unlock()
 	r.maybeCampaignOnWakeLocked(ctx)
 	// Propose an empty command which will wake the leader.
-	data := raftlog.EncodeRaftCommand(raftlog.EntryEncodingStandardWithoutAC, makeIDKey(), nil)
-	_ = r.mu.internalRaftGroup.Propose(data)
+	_ = r.mu.internalRaftGroup.Propose(nil)
 	return true
 }