raft: expose max message size in SendAppend

Epic: none
Release note: none

Author: pav-kv

pkg/raft/raft.go

@@ -606,12 +606,12 @@ func (r *raft) send(m pb.Message) {
 // if the follower log and commit index are up-to-date, the flow is paused (for
 // reasons like in-flight limits), or the message could not be constructed.
 func (r *raft) maybeSendAppend(to uint64) bool {
-	return r.maybeSendAppendImpl(to, r.enableLazyAppends)
+	return r.maybeSendAppendImpl(to, r.maxMsgSize, r.enableLazyAppends)
 }
 
 // maybeSendAppendImpl is the same as maybeSendAppend, but it supports the lazy
 // mode for StateReplicate, in which appends are not sent.
-func (r *raft) maybeSendAppendImpl(to uint64, lazy bool) bool {
+func (r *raft) maybeSendAppendImpl(to uint64, maxSize entryEncodingSize, lazy bool) bool {
 	pr := r.trk.Progress[to]
 	last, commit := r.raftLog.lastIndex(), r.raftLog.committed
 	msgAppType := pr.ShouldSendMsgApp(last, commit)
@@ -632,7 +632,7 @@ func (r *raft) maybeSendAppendImpl(to uint64, lazy bool) bool {
 
 	var entries []pb.Entry
 	if msgAppType == tracker.MsgAppWithEntries {
-		if entries, err = r.raftLog.entries(pr.Next, r.maxMsgSize); err != nil {
+		if entries, err = r.raftLog.entries(pr.Next, min(maxSize, r.maxMsgSize)); err != nil {
 			// Send a snapshot if we failed to get the entries.
 			return r.maybeSendSnapshot(to, pr)
 		}

pkg/raft/rawnode.go

@@ -125,25 +125,22 @@ func (rn *RawNode) Ready() Ready {
 	return rd
 }
 
-// SendAppend a log replication messages to a particular node. The message
+// SendAppend sends a log replication messages to a particular node. The message
 // will be available via next Ready.
 //
 // This method is used when Config.EnableLazyAppends is true. Typically, it
 // should be called before processing Ready, for all node IDs in StateReplicate
 // which have pending replication work.
 //
-// TODO(pav-kv): this should take and propagate maxBytes down the stack, for
-// integration with Admission Control. AC will be calling this method under two
-// conditions: the "send queue" is not empty (see EntriesReady), and there are
-// some spare send tokens (hence the maxBytes argument).
-//
-// TODO(pav-kv): as an intermediate step, we should pull Progress.Inflights out
-// of internals. This today plays the role of the send tokens tracker.
-func (rn *RawNode) SendAppend(to uint64) bool {
+// TODO(pav-kv): integrate with Admission Control, which will be calling this
+// under two conditions: the node's Next <= raftLog.lastIndex (i.e. the "send
+// queue" is not empty), and and there are some spare send tokens (hence the
+// maxSize parameter).
+func (rn *RawNode) SendAppend(to uint64, maxSize uint64) bool {
 	if !rn.raft.enableLazyAppends || to == rn.raft.id {
 		return false
 	}
-	return rn.raft.maybeSendAppendImpl(to, false /* lazy */)
+	return rn.raft.maybeSendAppendImpl(to, entryEncodingSize(maxSize), false /* lazy */)
 }
 
 // readyWithoutAccept returns a Ready. This is a read-only operation, i.e. there