313 lines
33 KiB
Markdown
313 lines
33 KiB
Markdown
# Design Document — controller-status (`ctrlstatus`)
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## Overview
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**Purpose:** add a single, cheap, read-only client→controller query — `ctrlstatus`, an XCE analog of LSF `lsid` — that returns basic cluster/controller identity and health: who is the current primary, the answering node's identity and role, the configured controllers (peers), the committed configuration version and content checksum, and a few HA health/progress fields (term, commit/apply position, fenced state, cluster name).
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**Users:** operators inspecting a running cluster, and test/E2E authors orchestrating failover (including `wait-primary`, which switches its probe to this query).
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**Impact:** today there is no status query — callers infer "is there a serving primary" indirectly (e.g. by listing jobs). This adds a new opcode by cloning the existing **opcode-only read** pattern of `clusterconf`, reads only already-maintained HA/config state (no behavior change), and crucially makes the query answerable on **any** node by adding it to the HA dispatch-gate allow-lists.
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### Goals
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- A new read-only opcode returning the status fields of Requirements 2–6 in one request/response (1.1, 1.4).
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- Answerable on **any** node — a standby reports a hint view (the primary it knows); an **authoritative** answer comes only from the primary, reached by following the redirect / rotating the master list (2.3, 7.1–7.3).
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- Report the loaded config version + content checksum (and the committed version) so same-version divergence is detectable (5.2, 5.3).
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- A `ctrlstatus` test-client command (8.x) and a `wait-primary` probe switched to an authoritative (primary-only) status query (9.x).
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### Non-Goals
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- No operator-facing CLI/REST `lsid` surface (Go tier) — later pass.
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- No change to HA election, replication, or commit behavior — the query only **reads** existing state.
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- No new configuration checksum computation — the committed-config SHA-256 already exists; this only exposes it.
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## Boundary Commitments
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### This Spec Owns
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- A new Cap'n Proto opcode `ctrlstatus` and its reply payload (`CtrlStatus`, `CtrlPeer`).
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- The controller handler `handle_ctrlstatus` that snapshots local HA/config state into the reply.
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- The **dispatch-gate allow-list entries** that let `ctrlstatus` answer in every controller role (incl. no-quorum).
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- The libxce client API (`xce_ctrlstatus_req` / `xce_ctrlstatus` / `xcecli_ctrlstatus` + free helper).
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- The `ctrlstatus` test-client command and the `wait-primary` probe switch.
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### Out of Boundary
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- The Go CLI/REST `lsid` surface (later spec).
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- Any change to how HA state (role, term, primary identity, committed config tag, commit/apply LSN, fence) is **produced or maintained** — this spec only reads it.
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- The existing `clusterconf` opcode and its resource/queue/worker payload (left unchanged).
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### Allowed Dependencies
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- The Cap'n Proto schema + build-time codegen (`src/schema/controller.capnp` → generated `controller.capnp.h/.c`).
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- The existing request/reply plumbing (`init_reply_by_req`, `xce_reply`, opcode-only `*_req` senders) and client failover wrapper (`XCECLI_FAILOVER_CALL`, `is_write=false`).
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- Read access to existing HA state (`ha_state_t`), config (`myconf_t`: `committed_config_tag`, `config_sha256`, `peers_cfg`), and persist accessors (`persist_recovery_unrecoverable`, `persist_durable_lsn`).
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### Revalidation Triggers
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- Any change to the `CtrlStatus`/`CtrlPeer` reply shape or the `ctrlstatus` opcode ordinal → re-check libxce decode + the test command + any future consumer.
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- Any change to the dispatch-gate role allow-lists → re-check that `ctrlstatus` still answers in every role and that no other opcode's gating widened.
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- A change to the meaning of `committed_config_tag` / `config_sha256` → re-check the version/checksum fields.
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## Architecture
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### Existing Architecture Analysis
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- **Opcode-only read precedent:** `clusterconf` is sent with no request body (`Request_body_nomsg`), dispatched in `cluster.c` `switch(request.opcode)`, handled by `handle_clusterconf` (`reply.c:10`), and returned via `xce_reply`. The client side is `xce_clusterconf` → `xcecli_clusterconf` (`XCECLI_FAILOVER_CALL`, `is_write=false`). **`ctrlstatus` clones this pattern.**
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- **No-alloc state-report precedent:** `ha_nop_reply_state_report` (`ha.c:3802`) reads HA atomics into a stack struct and points the reply union at it without heap allocation. `handle_ctrlstatus` follows this model (a small bounded peer list is the only allocation).
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- **Dispatch gate (the critical seam):** `ha_dispatch_gate` (`ha.c:4525`) is an allow-list keyed by role. The `CTRL_STANDBY` branch defaults to `-XCE_ERR_STANDBY`; `CTRL_INIT`/`CTRL_ELECTING` default to `-XCE_ERR_NOT_READY`; the `CTRL_PRIMARY` no-quorum branch allow-lists only specific reads. `clusterconf` is **not** in any standby allow-list — it is implicitly primary-only-when-serving. A status query must **not** inherit that; it must be explicitly allow-listed in every role branch.
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- **Config content checksum already exists:** `config_version_tag` = first 8 bytes of SHA-256 over the committed config blob; full digest in `config_sha256[32]`, round-trip-verified on load (`config_repl.c`).
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### Pattern & dependency direction
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Extend-in-place along the existing request path. Dependency direction (unchanged): `schema → libxce (request/reply/client) → controller handler`; the test client depends on libxce. No upward dependencies introduced.
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```mermaid
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graph LR
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TestClient[xce_test ctrlstatus and wait_primary] --> Libxce[libxce xcecli_ctrlstatus]
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Libxce --> Failover[XCECLI_FAILOVER_CALL is_write false]
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Failover --> Gate[ha_dispatch_gate allow_list all roles]
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Gate --> Handler[handle_ctrlstatus snapshots local state]
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Handler --> HAState[ha_state_t and myconf_t]
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Handler --> Reply[xce_reply CtrlStatus]
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```
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## File Structure Plan
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### Modified Files
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- `src/schema/controller.capnp` — add `OPCode ctrlstatus @40`; new `struct CtrlStatus $C.mapname("xce_ctrlstatus_t")` and `struct CtrlPeer $C.mapname("xce_ctrlpeer_t")`; reply-union member `ctrlstatus @17: CtrlStatus`. (Build regenerates `controller.capnp.h/.c` → `xce_ctrlstatus_t`, `RequestReply_data_ctrlstatus`, `free_CtrlStatus`.)
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- `src/controller/reply.c` — add `handle_ctrlstatus` (snapshot local HA/config state into a `CtrlStatus` reply; small peer list; `xce_reply`). Mirrors `handle_clusterconf`/`ha_nop_reply_state_report`.
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- `src/controller/cluster.c` — add `case OPCode_ctrlstatus: rc = handle_ctrlstatus(...)` to the opcode switch.
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- `src/controller/ha.c` — add `OPCode_ctrlstatus` to the `ha_dispatch_gate` allow-lists for `CTRL_PRIMARY` (incl. the no-quorum branch), `CTRL_STANDBY`, `CTRL_ELECTING`, `CTRL_INIT`. **(the requirements-critical change)**
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- `src/lib/request.c` + `src/include/request.h` — add `xce_ctrlstatus_req` (opcode-only sender, clone of `xce_clusterconf_req`).
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- `src/lib/xceapi.c` — add `xce_ctrlstatus` (send req, `cbuf_get` status, `MOVE_PTR` reply union).
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- `src/lib/client.c` + `src/include/client.h` — add `xcecli_ctrlstatus` (`XCECLI_FAILOVER_CALL`, `is_write=false`), the authoritative `xcecli_ctrlstatus_primary` (follows redirect / rotates the master list until `responderRole == PRIMARY`), and the `xcecli_free_ctrlstatus` macro.
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- `src/controller/testsuite/test.c` — add `cmd_ctrlstatus` + table registration (uses `xcecli_ctrlstatus`, shows the responder's view); switch `cmd_wait_primary`'s probe (currently `joblist_query(...)` at the deadline-loop call site) to `xcecli_ctrlstatus_primary` (authoritative, primary-only success).
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### New Files
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- None (capnp C types are generated; all handlers/APIs slot into existing TUs).
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## System Flows
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### Status query: any-node hint then authoritative-from-primary
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```mermaid
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sequenceDiagram
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participant C as Client
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participant S as Standby node
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participant P as Primary node
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C->>S: ctrlstatus request
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S-->>C: reply responderRole STANDBY plus known primary hint
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Note over C,S: Standby answer is a non authoritative hint view
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C->>P: re-query targeting the reported primary
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P-->>C: authoritative reply responderRole PRIMARY
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```
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The dispatch gate allow-lists `ctrlstatus` in every role (incl. no-quorum), so any node answers with its local view (satisfying any-node visibility). An **authoritative** answer comes only from the node whose `responderRole == PRIMARY`. When the first reply is from a non-primary, the client follows the redirect — it maps the reply's `primaryName` to an address via the reply's `peers` list (or rotates the configured master list) and re-queries — until it obtains the primary's authoritative reply or exhausts its budget. The plain `ctrlstatus` command may display the first (hint) reply with its "answered by" framing; `wait-primary` and any authoritative use require the primary's reply.
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Gate decision: `ctrlstatus` is allow-listed in every role branch and does not require quorum or a committed read — it returns the node's local view even when fenced or without quorum (precisely when an operator most wants it).
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### wait-primary probe (Req 9)
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`wait-primary` keeps its existing monotonic-deadline poll loop and timeout/exit semantics; only the probe changes from `joblist_query` to `xcecli_ctrlstatus`. Success predicate: the status reply reports a **non-`"unknown"`** current primary. On success it prints the served primary's identity. (Rationale + caveat below.)
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## Requirements Traceability
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| Requirement | Summary | Components | Interfaces |
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|-------------|---------|------------|------------|
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| 1.1, 1.2, 1.4 | Single-call read-only focused status | `handle_ctrlstatus`, `CtrlStatus` schema | opcode `ctrlstatus`, reply `CtrlStatus` |
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| 1.3 | "unknown" for undeterminable fields | `handle_ctrlstatus` | empty Text/sentinel mapping |
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| 2.1, 2.2, 2.3 | Current primary identity (unknown when unelected; standby's known primary) | `handle_ctrlstatus` (reads `ha->primary_host` under `ha->lock`) | `CtrlStatus.primaryName` |
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| 3.1, 3.2, 3.3 | Answered-by node + role, distinct from primary | `handle_ctrlstatus` | `CtrlStatus.responderName`, `responderRole` |
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| 4.1, 4.2 | Configured controllers + count | `handle_ctrlstatus` (reads `peers_cfg`) | `CtrlStatus.peers`, `peerCount` |
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| 5.1, 5.2, 5.3 | Config version + content checksum (loaded pair + committed) | `handle_ctrlstatus` (reads loaded `config_version_tag`/`config_sha256` + `committed_config_tag`) | `CtrlStatus.configVersion`, `configChecksum`, `committedConfigVersion` |
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| 6.1–6.4 | Term, commit/apply, fenced, cluster name | `handle_ctrlstatus` | `CtrlStatus.term`, `committedLsn`, `appliedLsn`, `fenced`, `clusterName` |
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| 7.1, 7.2, 7.3 | Failover-aware any-node delivery | `xcecli_ctrlstatus`, dispatch-gate allow-lists | `XCECLI_FAILOVER_CALL` (is_write=false), gate entries |
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| 8.1, 8.2, 8.3 | Test-client `ctrlstatus` command | `cmd_ctrlstatus` | client command + exit code |
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| 9.1–9.4 | wait-primary uses an authoritative (primary-only) status probe | `cmd_wait_primary` probe swap, `xcecli_ctrlstatus_primary` | redirect-to-primary, `responderRole == PRIMARY` success |
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## Components and Interfaces
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| Component | Layer | Intent | Req Coverage | Key Dependencies | Contracts |
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|-----------|-------|--------|--------------|------------------|-----------|
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| `CtrlStatus`/`CtrlPeer` schema | Schema | Reply payload for the status query | 2–6 | capnp codegen (P0) | API (reply) |
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| `handle_ctrlstatus` | Controller | Snapshot local HA/config state into the reply | 1–6 | `ha_state_t`, `myconf_t`, persist accessors (P0) | Service |
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| dispatch-gate allow-lists | Controller HA | Permit `ctrlstatus` in every role | 7 | `ha_dispatch_gate` (P0) | Service |
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| `xcecli_ctrlstatus` / `xcecli_ctrlstatus_primary` | libxce | Failover-aware read (any-node) + authoritative reach-primary read + free | 1, 7, 9 | failover wrapper, redirect hint (P0) | Service |
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| `cmd_ctrlstatus` | Test client | Print the status (responder view) | 8 | `xcecli_ctrlstatus` (P0) | State |
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| `cmd_wait_primary` probe | Test client | Authoritative serving-primary probe | 9 | `xcecli_ctrlstatus_primary` (P0) | State |
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### Schema — reply payload (Cap'n Proto)
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```capnp
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struct CtrlPeer $C.mapname("xce_ctrlpeer_t") {
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name @0: Text;
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host @1: Text;
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port @2: UInt32;
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}
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struct CtrlStatus $C.mapname("xce_ctrlstatus_t") {
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clusterName @0: Text;
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primaryName @1: Text; # empty ⇒ "unknown" (no elected/known primary)
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responderName @2: Text; # the node that answered
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responderRole @3: UInt8; # ctrl_role_t: INIT/ELECTING/PRIMARY/STANDBY
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term @4: UInt64;
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# Loaded config (consistent pair: version is the 8-byte prefix of the checksum)
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configVersion @5: UInt64; # loaded config_version_tag (8-byte SHA-256 prefix)
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configChecksum @6: Data; # loaded config_sha256 (full 32 bytes)
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# Committed config version (may differ from loaded mid config-change)
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committedConfigVersion @7: UInt64; # committed_config_tag
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committedLsn @8: UInt64;
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appliedLsn @9: UInt64;
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fenced @10: Bool; # in_catch_up OR recovery_unrecoverable
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peers @11: List(CtrlPeer) $C.mapname("peers.list") $C.maplistcount("peers.count");
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peerCount @12: UInt32;
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}
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```
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- **Config fields (Req 5):** `configVersion`/`configChecksum` are the **loaded** config's tag and full SHA-256 — a self-consistent pair (the version is the first 8 bytes of the checksum), so two nodes with identical loaded content match on both and divergent content differs on both (5.3). `committedConfigVersion` is the separately-tracked committed tag, exposing "what I run" vs "what is committed"; in steady state all three agree.
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- New OPCode ordinal: `ctrlstatus @40` (next free after `preVoteReply @39`). New reply-union member: `ctrlstatus @17` (next free after `walackreplymsg @16`). Field ordinals are append-only — never reuse/reorder.
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#### `handle_ctrlstatus` — Service contract
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| Field | Detail |
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|-------|--------|
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| Intent | Build a `CtrlStatus` from the responding node's local HA/config state and reply |
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| Requirements | 1.1–1.4, 2.1–2.3, 3.1–3.3, 4.1–4.2, 5.1–5.3, 6.1–6.4 |
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**Responsibilities & Constraints**
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- Read-only: must not modify any HA, persist, or config state (1.2).
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- Field sourcing: `clusterName`/`responderName` from `c->myconf`/own peerinfo; `responderRole`, `term`, `appliedLsn`, `committedLsn`, `committedConfigVersion` (`committed_config_tag`) via `atomic_load_explicit(..., acquire)`; `configVersion` from the loaded `config_version_tag` and `configChecksum` from the loaded `config_sha256[32]` (a self-consistent pair — Req 5.3); `primaryName`/peers as below; `fenced = in_catch_up || persist_recovery_unrecoverable(...)`.
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- **Locking:** `primary_host`/`primary_port` are guarded by `ha->lock` — take it for a consistent snapshot, copy out, release. All other fields are atomics or immutable config.
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- **"unknown" mapping (1.3, 2.2, 2.3):** if `primary_host[0] == '\0'` (no known primary), emit an empty `primaryName`, which the client renders as `"unknown"`.
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- **Peers (4.x):** iterate `c->myconf->peers_cfg.candidates[0..count-1]` → one `CtrlPeer{name,host,port}` each; set `peerCount`.
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- Answerable in every role; returns the local view even when fenced/no-quorum.
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**Dependencies**
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- Inbound: `cluster.c` opcode switch — routes the request (P0).
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- Outbound: `ha_state_t`, `myconf_t`, persist accessors — read-only snapshot (P0).
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- Outbound: `init_reply_by_req`, `xce_reply` — reply encode/send (P0).
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#### Dispatch-gate allow-lists — Service contract
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- Add `OPCode_ctrlstatus` to the allow-list in `ha_dispatch_gate` for `CTRL_PRIMARY` (including the no-quorum branch), `CTRL_STANDBY`, `CTRL_ELECTING`, and `CTRL_INIT` (7.1, 7.2).
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- Constraint: the change is scoped strictly to `ctrlstatus`; no other opcode's gating may widen. `ctrlstatus` never requires quorum or a committed read.
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#### libxce client API — Service contract
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```c
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/* opcode-only request sender (clone of xce_clusterconf_req) */
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int xce_ctrlstatus_req(endpoint_t* ep);
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/* send + await reply; on success MOVE_PTR the reply union out */
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int xce_ctrlstatus(xce_ctx_t* ctx, xce_ctrlstatus_t** status);
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/* failover-aware read (is_write=false): returns whatever node answers (may be a
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* standby hint view). Use for the operator command. */
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int xcecli_ctrlstatus(xcecli_ctx_t c, xce_ctrlstatus_t** status);
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/* AUTHORITATIVE read: returns only a reply whose responderRole == PRIMARY. If the
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* first answer is from a non-primary, follow the redirect — target the reported
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* primaryName via the reply's peers list, else rotate the configured master list
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* — until the primary answers or the failover budget is exhausted. */
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int xcecli_ctrlstatus_primary(xcecli_ctx_t c, xce_ctrlstatus_t** status);
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#define xcecli_free_ctrlstatus(s) xce_free_ctrlstatus(s)
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```
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- Preconditions: valid client context.
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- Postconditions: on success `*status` owns a decoded `CtrlStatus` (caller frees); on failure returns a typed negative (7.3) and `*status` untouched. For `xcecli_ctrlstatus_primary`, success additionally guarantees `responderRole == PRIMARY` (an authoritative answer).
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- Invariants: `is_write=false` — retryable/rotatable across the configured controllers.
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#### `cmd_ctrlstatus` (test client) — State contract
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- Calls `xcecli_ctrlstatus`; on success prints the fields in human-readable form (8.1) — `Primary`, `answered by <responderName> (<role>)` distinct from `Primary:` (3.3), peers + count, `configVersion` and `committedConfigVersion`, `configChecksum` as hex, term, commit/apply, fenced, cluster name; renders empty `primaryName` as `unknown`. Returns 0 on success, `<0` on failure with the error printed (8.2, 8.3). Frees the reply.
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#### `cmd_wait_primary` probe swap — State contract
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- Replace the single `joblist_query(...)` probe call in the deadline loop with `xcecli_ctrlstatus_primary` (the authoritative variant).
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- **Success predicate (9.1, 9.2):** the probe obtains an authoritative reply with `responderRole == PRIMARY` (the answer came from the serving primary). On success, complete and print that primary's identity. A standby-only/hint answer is NOT success — the probe follows the redirect to the primary (or keeps polling) until the primary answers or the deadline elapses.
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- **Decision (resolves review Issue 1):** require the answer to come **from the primary**, not merely "a primary name was reported by some node." This avoids a false success on a standby's stale `primary_host` after a primary death (the false-positive class removed from the durability soak) and faithfully meets Req 9.1's "**serving** primary." The any-node hint view remains available for the operator `ctrlstatus` command via `xcecli_ctrlstatus`.
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- **Preserved (9.4):** the timeout-argument parsing, monotonic deadline, poll interval, log-level quieting, and success/failure exit codes are unchanged; only the probe call and the success message change.
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## Data Models
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The only new data is the reply payload above. `CtrlStatus` is a flat value object (no persistence, no aggregate); `CtrlPeer` is a bounded value list (≤ configured controller count, typically 3). `configChecksum` is the loaded config's 32-byte SHA-256 and `configVersion` is its own 8-byte prefix (a self-consistent pair); `committedConfigVersion` is the separately-tracked committed tag. Two nodes with identical loaded config content produce identical `configVersion` + `configChecksum`; differing content differs in both (5.3). A node mid config-change may show `configVersion != committedConfigVersion`.
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## Error Handling
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- **No reachable controller (7.3):** `xcecli_ctrlstatus` returns the failover wrapper's typed negative (e.g. no-master/timeout); `cmd_ctrlstatus` prints it and returns non-zero (8.3); `wait-primary` keeps polling until its deadline (9.3).
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- **Undeterminable field (1.3):** emit the defined "unknown"/empty value, never uninitialized data.
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- **Standby with no known primary (2.3):** `primaryName` empty → "unknown"; the call still succeeds (the status itself is valid).
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- **Read-only guarantee (1.2):** the handler takes only read locks/atomic loads; no state mutation on any path.
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## Testing Strategy
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### Unit / handler
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- `handle_ctrlstatus` on a PRIMARY returns `primaryName==self`, `responderRole==PRIMARY`, populated peers/version/checksum (2.1, 3.x, 4.x, 5.x).
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- `handle_ctrlstatus` on a STANDBY with a known primary returns that primary and `responderRole==STANDBY`; with no known primary returns empty `primaryName` (2.2, 2.3).
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- `fenced` reflects `in_catch_up`/`recovery_unrecoverable` (6.3); the handler mutates no state (1.2).
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- `configVersion`/`configChecksum` are a self-consistent loaded pair — equal across two nodes with identical loaded config, differ when content differs; `committedConfigVersion` is exposed separately (5.1, 5.2, 5.3).
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### Integration
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- Dispatch-gate: a `ctrlstatus` request is answered (not `-XCE_ERR_STANDBY`/`-XCE_ERR_NOT_READY`) on STANDBY, ELECTING, INIT, and PRIMARY-no-quorum nodes; no other opcode's gating changed (7.1, 7.2).
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- libxce round-trip: `xcecli_ctrlstatus` decodes all fields; `is_write=false` rotates across configured controllers; no-reachable-controller returns a typed failure (7.3).
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- Authoritative read: `xcecli_ctrlstatus_primary`, when the first answer is from a standby, follows the redirect to the primary and returns a reply with `responderRole == PRIMARY`; it never returns a standby/hint reply as the authoritative result (9.1, 9.2).
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### E2E (live `/xce-deploy-ha`)
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- `ctrlstatus` against a healthy 3-node cluster prints the primary, peers, version+checksum; querying a standby still reports the primary with `answered by <standby>` (2.3, 8.1).
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- `wait-primary` (authoritative probe) returns immediately on a healthy cluster and names the primary; after a primary kill, blocks until the **new primary itself** answers, then names it; does NOT false-succeed on a standby's stale primary view; times out when no primary serves (9.1–9.4). Directly useful to the `ha-commit-durability` Phase 6 liveness/>60s-election investigation.
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## Security Considerations
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`ctrlstatus` exposes cluster topology, role, term, and config version/checksum — the same trust level as the existing `clusterconf`/state-report reads (no secrets, no config content, no job data). It is read-only and goes through the same authenticated client path as other client ops; no new authorization surface is introduced. Broadening the dispatch gate is scoped strictly to this one read opcode.
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---
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## Design Delta — Requirements 10 & 11 (2026-06-20)
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> **Merge note (as-built correction).** The handler shipped as `ctrlstatus_fill` + `handle_ctrlstatus` in **`src/controller/ctrlstatus.c`** (not `reply.c`); `configChecksum` is carried as **Text** lowercase-hex (the `Data` capnp type maps to the project's structured `xce_data_t`); `primaryName` is **role-derived** (primary → self, else empty) after E2E fix `ade0081` — `ha->primary_host` is vestigial. The Req 10/11 changes are written against this as-built reality; the Reqs 1–9 design above stands as the original record.
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### What changed and why
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Live E2E (2026-06-20): a standby's `ctrlstatus` reported `committedLsn: 0` / `committedConfigVersion: 0` while `appliedLsn: 38` — an apparent commit/apply inversion — because `ctrlstatus_fill` reads the **primary-only** markers `persist.committed_lsn` (`ctrlstatus.c:130`) and `ha->committed_config_tag` (`:109`), which stay `0` on a node that never led. And there was no responder timestamp to line a captured status up against `ctrl-N.log`. Req 10 fixes the off-primary committed sourcing; Req 11 adds a responder snapshot timestamp.
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### Boundary Commitments (delta)
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- **This spec owns (added):** the off-primary field-sourcing fix inside `ctrlstatus_fill` (read the *learned* committed values when not primary); a new read-only `CtrlStatus.responderTimeMs` field stamped at snapshot time; its render in `cmd_ctrlstatus`.
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- **Out of Boundary (firm):** making the off-primary committed value **live-fresh** — i.e. consuming `HeartbeatMsg.committedLsn` / extending `OP_nop` to refresh `last_known_committed_lsn` on every heartbeat — is a heartbeat/replication-protocol change. It violates Req 10.4 and is routed to **ha-heartbeat-liveness** / **ha-repl-hardening**. controller-status reports the honest best-known value only. (Note: superseded by **ha-heartbeat-committed-propagation** — that spec implemented exactly this, adding `ha_consume_heartbeat_committed`/`ha_observe_heartbeat_committed`, invoked from the primary's heartbeat in `cluster.c`, which now refreshes `last_known_committed_lsn`/`last_known_committed_config_tag` on every heartbeat, term-guarded and monotonic. See that spec's design.md.)
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- **Allowed Dependencies (added):** read access to `ha->last_known_committed_lsn` (`_Atomic uint64_t`, `ha.h:183`) and `ha->last_known_committed_config_tag` (`ha.h:185`); `clock_gettime(CLOCK_REALTIME)`; the existing `xcelog.h` wall-clock format for client rendering. (Note: `last_known_committed_config_tag` is now also `_Atomic uint64_t` — migrated by ha-heartbeat-committed-propagation from the plain `uint64_t` this design was written against.)
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- **Revalidation Triggers (added):** any change to where/when `last_known_committed_lsn`/`last_known_committed_config_tag` are written (today: `cluster_apply_ctrlhello_reply` at join/RDHUP, `ha_observe_heartbeat_committed` on every heartbeat, and the election safe-commit path) → re-check the off-primary committed reporting and the staleness caveat. (Note: the heartbeat writer was added by ha-heartbeat-committed-propagation, superseding the "join/RDHUP only" premise below.)
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### Locked design decisions (from research items)
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1. **Req 10 sourcing → role-branch (not uniform `max()`).** When `responderRole == CTRL_PRIMARY`, keep the node's own authoritative live markers (`persist.committed_lsn`, `ha->committed_config_tag`). Otherwise report the learned pair (`ha->last_known_committed_lsn`, `ha->last_known_committed_config_tag`). Rationale: a standby's learned value is its only honest "committed" knowledge; a primary's own marker is authoritative and must not be shadowed by a possibly-stale learned value. (Mirrors the `last_known_*` read precedent at `ha.c:5319` (`ha_vote_self_freshness`), `ha.c:6732`.)
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2. **Req 10 staleness caveat (documented behavior, not a bug).** `last_known_committed_lsn` is refreshed at **CtrlHello join / RDHUP-failover**, not per heartbeat, so an off-primary committed value MAY lag the live primary between joins. This is the in-boundary contract; live-fresh is the out-of-boundary item above. The `0`-inversion is eliminated regardless (a standby that has joined has a non-zero learned value; a never-joined node correctly reports `0` = unknown, per Req 1.3 / 10.2). (Note: superseded by **ha-heartbeat-committed-propagation** — `last_known_committed_lsn`/`_config_tag` are now also refreshed on every heartbeat via `ha_observe_heartbeat_committed`, so the join/RDHUP-only staleness window described here no longer applies; see that spec's design.md.)
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3. **Req 11 wire type → `UInt64` epoch-milliseconds.** Numeric, locale-safe; the client formats it. (Pre-formatted `Text` was the alternative; rejected to keep the wire value machine-comparable and avoid encoding a locale into the reply.)
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4. **Req 11 clock → `CLOCK_REALTIME`, stamped in `ctrlstatus_fill` at snapshot time.** NOT `CLOCK_MONOTONIC` (which `ha_on_heartbeat_received` uses for liveness) — monotonic is not wall-clock and cannot be correlated to logs. The client renders the millis to local `YYYY-MM-DD HH:MM:SS,mmm` using the `xcelog.h` convention so it is directly comparable to a log line.
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### Research item carried to implementation
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- Confirm the exact wall-clock formatter/helper in `src/include/xcelog.h` and reuse it (or match its `YYYY-MM-DD HH:MM:SS,mmm` form) in `cmd_ctrlstatus` so the printed timestamp is byte-comparable to `ctrl-N.log`. `last_known_committed_config_tag` was non-atomic at design time (written under lock in `ha_convergence.c`); the status read was planned as a best-effort aligned 8-byte load (acceptable for a reporting snapshot) — do not add locking on the read path. (Note: superseded by **ha-heartbeat-committed-propagation**, which migrated the field to `_Atomic uint64_t` at `ha.h:185`, written via `atomic_store_explicit` at `ha_convergence.c:368` and `ha.c:9011`; the as-built `ctrlstatus_fill` correctly reads it with `atomic_load_explicit`, not a bare aligned load.)
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### Schema delta (Cap'n Proto)
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Append one field to `CtrlStatus` (next free ordinal `@13`, after `peerCount @12`; append-only, never reorder):
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```capnp
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responderTimeMs @13: UInt64 $C.mapname("responder_time_ms"); # CLOCK_REALTIME epoch millis at snapshot (Req 11.1)
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```
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No change to `committedLsn @8` / `committedConfigVersion @7` wire shape — Req 10 changes only the **value source**, not the field.
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### `ctrlstatus_fill` delta — Service contract (`src/controller/ctrlstatus.c`)
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- **Req 10 (committed sourcing):** replace the unconditional reads at `ctrlstatus.c:108–110,130` with the role-branch above:
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- `responderRole == CTRL_PRIMARY` → `committedLsn = persist.committed_lsn`, `committedConfigVersion = ha->committed_config_tag` (atomic acquire loads, unchanged).
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- else → `committedLsn = ha->last_known_committed_lsn` (atomic acquire), `committedConfigVersion = ha->last_known_committed_config_tag` (plain aligned load).
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- `appliedLsn` (`ha->applied_lsn`) is unchanged — it is already correct in every role.
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- **Req 11 (timestamp):** stamp `st->responder_time_ms` from `clock_gettime(CLOCK_REALTIME)` (`tv_sec*1000 + tv_nsec/1e6`) at the top of the snapshot, before/with the other field loads, so it marks the responder's sample moment.
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- **Read-only invariant (10.4, 1.2) preserved:** all additions are atomic/aligned loads + a clock read; no HA/persist/config mutation.
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### `cmd_ctrlstatus` delta — State contract (`src/controller/testsuite/test.c`)
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- Print one added line rendering `responder_time_ms` as local `YYYY-MM-DD HH:MM:SS,mmm` (xcelog.h form) alongside the existing fields (Req 11.3). The committed lines need no rendering change — Req 10 only changes the values they already print.
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### File Structure Plan (delta)
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**Modified files:**
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- `src/schema/controller.capnp` — add `responderTimeMs @13: UInt64` to `CtrlStatus` (regen `controller.capnp.h/.c` → `xce_ctrlstatus_t.responder_time_ms`).
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- `src/controller/ctrlstatus.c` — `ctrlstatus_fill`: role-branch committed sourcing (Req 10) + `CLOCK_REALTIME` timestamp stamp (Req 11).
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- `src/controller/testsuite/test.c` — `cmd_ctrlstatus`: render the responder timestamp line (Req 11.3).
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- `src/controller/testsuite/test_ctrlstatus.c` — add/extend unit tests (below).
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No new files (the capnp field is generated; all logic slots into existing TUs).
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### Requirements Traceability (delta)
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| Requirement | Summary | Components | Interfaces |
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|-------------|---------|------------|------------|
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| 10.1 | Off-primary reports *learned* committed LSN + config version | `ctrlstatus_fill` role-branch | `CtrlStatus.committedLsn`, `committedConfigVersion` (value source = `ha->last_known_committed_*`) |
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| 10.2 | No learned value yet → 0/unknown | `ctrlstatus_fill` | `last_known_committed_lsn == 0` (correct unknown, per 1.3) |
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| 10.3 | No spurious applied>committed inversion | `ctrlstatus_fill` | `appliedLsn` vs role-correct `committedLsn` |
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| 10.4 | Read-only reporting; no production/replication change | `ctrlstatus_fill`; out-of-boundary routing | atomic/aligned loads only |
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| 11.1 | Responder wall-clock at sample time | `ctrlstatus_fill` (`CLOCK_REALTIME`) | `CtrlStatus.responderTimeMs` |
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| 11.2 | Same clock/format as logs | `cmd_ctrlstatus` render (xcelog.h form) | local `YYYY-MM-DD HH:MM:SS,mmm` |
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| 11.3 | Test client prints the timestamp | `cmd_ctrlstatus` | added print line |
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### Testing Strategy (delta)
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**Unit (`test_ctrlstatus.c`, TDD red→green):**
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- STANDBY with `last_known_committed_lsn = 36`, `persist.committed_lsn = 0`, `applied_lsn = 38` → reply reports `committedLsn == 36` (not 0) and `appliedLsn == 38` (no inversion below the learned value) (10.1, 10.3).
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- STANDBY pre-join (`last_known_committed_lsn == 0`) → reply reports `committedLsn == 0` / `committedConfigVersion == 0` (correct unknown) (10.2).
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- PRIMARY → reply reports `committedLsn == persist.committed_lsn` and `committedConfigVersion == ha->committed_config_tag` (authoritative own markers unchanged) (10.1 primary branch).
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- `committedConfigVersion` off-primary equals `last_known_committed_config_tag` (symmetry with the LSN) (10.1).
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- `responder_time_ms` is non-zero and within a tolerance of a test-captured `CLOCK_REALTIME` sample; the handler still mutates no state (11.1, 1.2/10.4).
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**Integration / round-trip (libxce):** `xcecli_ctrlstatus` decodes the new `responderTimeMs` field end-to-end (no manual decode — codegen), proving wire compatibility.
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**E2E (live `/xce-deploy-ha`):** reproduce the original finding — submit jobs so the primary commits, query a **standby**; assert the standby's `committedLsn` is non-zero and tracks (within the join-refresh caveat) rather than `0`, and that the printed `responder timestamp` matches the standby's own `ctrl-N.log` line for that query. (Note: the "join-refresh caveat" is narrower than described above — ha-heartbeat-committed-propagation added per-heartbeat refresh, so tracking is now near-live rather than join/RDHUP-only; see that spec's design.md.)
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