Wire Compatibility

DSM runtime sync supports rolling upgrades across a bounded wire-version window. Current dsm-sync services advertise:

Field	Value
minimum supported wire version	2
maximum supported wire version	4
preferred peer-to-peer wire version	4

Send Rules

• Legacy broadcast traffic uses the minimum supported version, currently 2.
• Peer-targeted traffic uses the highest negotiated common version, capped by the local preferred version.
• Batch register delta broadcasts use wire version 4 only when delta coalescing is enabled and every active peer advertises both wire-version 4 support and the batch-delta-sync capability.
• Peers that do not advertise min_wire_version and max_wire_version are treated as 2/2.

Capability Advertisement

CapabilityAdvertisement carries three forms of the capability set:

Field	Type	Purpose
capability_bits	bytes	Legacy packed byte mask.
capability_name	repeated string	Human-readable compatibility form.
capability_bits_v2	uint64	Preferred fixed-width mask for current peers.

Readers consume capability state in this order: capability_bits_v2, then capability_bits, then capability_name.

Advertised Capabilities

Bit	Wire name	Feature
0	runtime	Baseline runtime v2 protocol.
1	collection-routing	Collection-addressed routing.
2	descriptor-advertisement	Collection descriptor advertisement.
3	register-delta-sync	Register delta replication.
4	lease-control	Lease collection management.
5	verify-current	Verify-current lease fencing check.
6	fencing-reject	Fencing-based write rejection.
7	reliable-data-plane	Reliable data-plane transport.
8	snapshot-streaming	Snapshot-based repair.
9	crdt-delta-sync	CRDT delta replication.
10	batch-delta-sync	Batched register delta broadcasts.
11	suspicion-protocol	SWIM-style suspicion before FAILED.
12	proactive-anti-entropy	Background anti-entropy sweep.
13	payload-encryption	Per-envelope AEAD payload encryption.
14	conflict-resolver	Pluggable per-collection conflict resolver.
15	adaptive-repair	EWMA-based adaptive snapshot/replay planner.

Capabilities 11-15 are informational. They describe active runtime features but do not directly downgrade send paths.

Trace Context Fields

PlatformEnvelope can carry optional W3C trace context:

Field	Number	Meaning
trace_parent	21	W3C traceparent from the current TraceContextHolder.
trace_state	22	Optional W3C tracestate.

Older peers ignore these fields through protobuf unknown-field tolerance. No wire-version gate is required.

Compatibility Matrix

Local node	Remote node	Traffic kind	Selected version	Outcome
v2-only	v2-only	any	2	works
v4-capable	v2-only	legacy broadcast	2	works
v4-capable	v2-only	targeted	2	works
v4-capable	v3-capable	targeted	3	works
v4-capable	v4-capable without batch-delta-sync	register broadcast	2	legacy delta sync
v4-capable	v4-capable with batch-delta-sync	coalesced register broadcast	4	batch delta sync
current node	peer < 2	inbound	n/a	dropped as too old
current node	peer > 4	inbound	n/a	dropped as too new

Digest Encoding

Wire version	Digest behavior
2	Legacy per-entry digest list.
3	Compact digest with aggregate hash and bucket hashes.
4	Same compact digest plus batch register delta envelopes when enabled.

Rollout Guidance

1. Deploy nodes that understand versions 2 through 4.
2. Allow capability advertisements to propagate.
3. Let targeted traffic negotiate higher common versions automatically.
4. Keep legacy broadcasts on version 2 while mixed-version peers exist.
5. Enable dsm.sync.delta-coalescing.enabled=true only after every active peer advertises version 4 and batch-delta-sync.

Related Pages

• Sync Protocol
• Repair And Anti-Entropy
• Spring Properties