kv/kvserverpb: rename RaftCommandFooter to MaxLeaseFooter

Now that `ClosedTimestampFooter` exists, be more specific and symmetric.

pkg/kv/kvserver/kvserverpb/proposer_kv.go

@@ -16,7 +16,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 )
 
-var maxRaftCommandFooterSize = (&RaftCommandFooter{
+var maxMaxLeaseFooterSize = (&MaxLeaseFooter{
 	MaxLeaseIndex: math.MaxUint64,
 }).Size()
 
@@ -28,10 +28,10 @@ var maxClosedTimestampFooterSize = (&ClosedTimestampFooter{
 	},
 }).Size()
 
-// MaxRaftCommandFooterSize returns the maximum possible size of an
-// encoded RaftCommandFooter proto.
-func MaxRaftCommandFooterSize() int {
-	return maxRaftCommandFooterSize
+// MaxMaxLeaseFooterSize returns the maximum possible size of an encoded
+// MaxLeaseFooter proto.
+func MaxMaxLeaseFooterSize() int {
+	return maxMaxLeaseFooterSize
 }
 
 // MaxClosedTimestampFooterSize returns the maximmum possible size of an encoded

pkg/kv/kvserver/kvserverpb/proposer_kv.proto

@@ -241,7 +241,12 @@ message RaftCommand {
   // updated accordingly. Managing retry of proposals becomes trickier as
   // well as that uproots whatever ordering was originally envisioned.
   //
-  // This field is set through RaftCommandFooter hackery.
+  // This field is set through MaxLeaseFooter hackery. Unlike with the
+  // ClosedTimestamp, which needs to be nullable in this proto (see comment),
+  // there are no nullability concerns with this field. This is because
+  // max_lease_index is a primitive type, so it does not get encoded when zero.
+  // This alone ensures that the field is not encoded twice in the combined
+  // RaftCommand+MaxLeaseFooter proto.
   uint64 max_lease_index = 4;
 
   // The closed timestamp carried by this command. Once a follower is told to
@@ -287,17 +292,17 @@ message RaftCommand {
   reserved 1, 2, 10001 to 10014;
 }
 
-// RaftCommandFooter contains a subset of the fields in RaftCommand. It is used
+// MaxLeaseFooter contains a subset of the fields in RaftCommand. It is used
 // to optimize a pattern where most of the fields in RaftCommand are marshaled
 // outside of a heavily contended critical section, except for the fields in the
 // footer, which are assigned and marhsaled inside of the critical section and
 // appended to the marshaled byte buffer. This minimizes the memory allocation
 // and marshaling work performed under lock.
-message RaftCommandFooter {
+message MaxLeaseFooter {
   uint64 max_lease_index = 4;
 }
 
-// ClosedTimestampFooter is similar to RaftCommandFooter, allowing the proposal
+// ClosedTimestampFooter is similar to MaxLeaseFooter, allowing the proposal
 // buffer to fill in the closed_timestamp field after most of the proto has been
 // marshaled already.
 message ClosedTimestampFooter {

pkg/kv/kvserver/replica_proposal.go

@@ -81,7 +81,7 @@ type ProposalData struct {
 	quotaAlloc *quotapool.IntAlloc
 
 	// tmpFooter is used to avoid an allocation.
-	tmpFooter kvserverpb.RaftCommandFooter
+	tmpFooter kvserverpb.MaxLeaseFooter
 
 	// ec.done is called after command application to update the timestamp
 	// cache and optionally release latches and exits lock wait-queues.