25_software_house_api

Example 25 — Software-House Task Graph (persistent REST API)

A small, production-shaped REST service built on GoGraph. It models task management inside a software-house as a single multi-layer Labeled Property Graph (LPG) and answers the questions a maintenance team actually asks — change impact, code ownership, bus-factor, workload, blocked work, dependency cycles — in Cypher, over one graph that spans code, work and people.

It is built on the Go standard library only (net/http, zero new dependencies) and is persistent across restarts and kill -9 safe (write-ahead log + snapshot + recovery).

It also demonstrates GoGraph's schema surface: Cypher DDL (CREATE CONSTRAINT / CREATE INDEX), UNIQUE-constraint enforcement (409 on a duplicate), schema introspection via the built-in db.* procedures (GET /schema), and query-plan explanation (POST /explain, index seek vs label scan) — all of it durable across a restart.

• Data model, REST contract and query catalogue: SPEC.md
• Runtime reference: the package doc in doc.go

The multi-layer model

Three layers live in one LPG. Every node carries a layer label (Code / Work / People) and a type label. Two inter-layer edges, ASSIGNED_TO and TOUCHES, form the spine that makes cross-layer questions a single Cypher pattern.

   People layer            Work layer                     Code layer
  ┌────────────┐  ASSIGNED_TO  ┌──────┐     TOUCHES     ┌───────────┐
  │ Developer  │──────────────▶│ Task │────────────────▶│ Component │
  │ Team       │               │ Sprint                 │ Module    │
  └────────────┘               │ WorkflowState          │ Repository│
     MEMBER_OF                  └──────┘                 └───────────┘
                         SUBTASK_OF / NEXT          CONTAINS / DEPENDS_ON
                         BLOCKS / HAS_STATE
                         IN_SPRINT

DEPENDS_ON (dependent → dependency) is the dependency graph; composed with the spine it answers "if I change X, who is affected?". Completed work carries TOUCHES edges (realised history); planned work carries only ASSIGNED_TO {state:'planned'}. See SPEC.md for the full schema.

Build and run

# from the repository root — small deterministic fixture
go run ./examples/25_software_house_api -d ./data -addr :8080

# observable-scale run: a seeded synthetic graph (~5.7k nodes, ~19k edges)
go run ./examples/25_software_house_api -d ./big -addr :8081 \
    -scale-components 2000 -scale-tasks 1500 -scale-developers 80 -scale-seed 7

-d is the data directory (created if missing); -addr is the listen address (default :8080). Press Ctrl-C (SIGINT) or send SIGTERM for a graceful shutdown that writes a final snapshot and closes the WAL.

Scale and flags

With every -scale-* flag at 0 the server loads exactly the 46-node / 106-edge hand-authored fixture below — the small deterministic default the regression tests pin. Setting any -scale-* flag grows the same multi-layer model with a seeded, reproducible synthetic layer (keys prefixed syn:, so no hand-authored key is ever touched), up to a size where query latency, live heap, and bytes-per-element become observable. The same scale can be requested per call via the POST /seed body (see below). The synthetic topology is described in synth.go: a Price-model power-law dependency DAG with a bounded number of injected cycles, ownership clustered by developer home-module affinity (so bus-factor risk is realistic), and shallow BLOCKS chains — so every maintenance query stays meaningful at scale.

Endpoints

Seed the graph

curl -s -XPOST localhost:8080/seed

{"seeded":true,"status":"ok","scale_components":0,"scale_tasks":0,"scale_developers":0}

Running it again is a no-op ("seeded":false). The default fixture is 46 nodes and 106 edges across the three layers.

To grow it with a seeded synthetic layer, post the scale in the body:

curl -s localhost:8080/seed -d '{"scale_components":2000,"scale_tasks":1500,"scale_developers":80,"scale_seed":7}'

{"seeded":true,"status":"ok","scale_components":2000,"scale_tasks":1500,"scale_developers":80}

The synthetic layer commits in the same atomic transaction as the base fixture, so it is applied exactly once and survives a kill -9 (the next reopen replays the whole seed from the WAL). A given scale_seed reproduces the same graph byte-for-byte.

Inspect the counts and telemetry

curl -s localhost:8080/stats

The response splits deterministic facts (nodes, edges) from volatile telemetry (telemetry). The facts are reproducible for a fixed seed and scale; every telemetry field varies per run and per machine — the JSON analogue of the # telemetry convention the non-server examples use.

{
  "nodes": {"Repository":1,"Module":5,"Component":12,"Task":14,
            "Sprint":2,"WorkflowState":4,"Developer":6,"Team":2},
  "edges": {"CONTAINS":17,"DEPENDS_ON":17,"SUBTASK_OF":2,"NEXT":4,
            "BLOCKS":3,"HAS_STATE":14,"IN_SPRINT":14,"MEMBER_OF":6,
            "ASSIGNED_TO":16,"TOUCHES":13},
  "telemetry": {
    "heap_alloc_bytes": 10590968, "heap_alloc_human": "10.10 MiB",
    "heap_sys_bytes": 45449216, "num_gc": 19,
    "bytes_per_element": 461.0,
    "query_count": 0, "write_count": 0, "stats_count": 1,
    "last_query_ms": 0, "max_query_ms": 0,
    "stats_sweep_ms": 80.72, "seed_ms": 62.83
  }
}

(The telemetry values above are illustrative — they change every run.)

The server's own startup log on stderr follows the same split for a scaled run:

seed.scale_components=2000           # fact — reproducible for a fixed seed
seed.scale_tasks=1500                # fact
# seed.elapsed=63ms                  # telemetry — varies, never pinned
# seed.node_rate=59896 nodes/s       # telemetry
# mem.heap_alloc=9.46 MiB            # telemetry

Run a query

POST /query takes {"query": "<cypher>", "params": {<optional>}} and returns {"columns": [...], "rows": [{...}]}. Because some queries below contain Cypher string literals ('done'), the examples post the body via a quoted heredoc so the shell leaves it untouched:

curl -s localhost:8080/query -d @- <<'JSON'
{"query":"MATCH (u:Developer) RETURN u.key AS dev ORDER BY dev"}
JSON

A write is durable the moment the response returns:

curl -s localhost:8080/query -d @- <<'JSON'
{"query":"CREATE (d:Developer:People {key:'dev:zoe', name:'Zoe'}) RETURN d.key AS key"}
JSON

{"columns":["key"],"rows":[{"key":"dev:zoe"}]}

The maintenance-query catalogue

These eight queries are the point of the example: each is a real software- maintenance question answered over the multi-layer graph. Outputs below are the actual responses against the seeded fixture.

Q1 — Change impact / blast radius

If comp:platform/config.go changes, which components are affected, and which tasks and developers must be told?

MATCH (x:Component {key:$k})
MATCH (affected:Component)-[:DEPENDS_ON*0..]->(x)
OPTIONAL MATCH (dev:Developer)-[:ASSIGNED_TO]->(t:Task)-[:TOUCHES]->(affected)
RETURN affected.key AS component,
       collect(DISTINCT t.key)   AS impactedTasks,
       collect(DISTINCT dev.key) AS impactedDevelopers
ORDER BY component

curl -s localhost:8080/query -d @- <<'JSON'
{"query":"MATCH (x:Component {key:$k}) MATCH (affected:Component)-[:DEPENDS_ON*0..]->(x) OPTIONAL MATCH (dev:Developer)-[:ASSIGNED_TO]->(t:Task)-[:TOUCHES]->(affected) RETURN affected.key AS component, collect(DISTINCT t.key) AS impactedTasks, collect(DISTINCT dev.key) AS impactedDevelopers ORDER BY component","params":{"k":"comp:platform/config.go"}}
JSON

config.go is the most foundational file, so all 12 components come back. First rows:

{"component":"comp:api/handlers.go","impactedTasks":["task:WS-8"],"impactedDevelopers":["dev:alice"]}
{"component":"comp:catalog/repository.go","impactedTasks":["task:WS-4"],"impactedDevelopers":["dev:bob","dev:alice"]}

Q2 — Code ownership ("who knows this code")

MATCH (dev:Developer)-[:ASSIGNED_TO]->(:Task)-[r:TOUCHES]->(c:Component {key:$k})
RETURN dev.key AS developer, count(r) AS touches, sum(r.churn) AS totalChurn
ORDER BY totalChurn DESC

{"columns":["developer","touches","totalChurn"],
 "rows":[{"developer":"dev:erin","touches":1,"totalChurn":120},
         {"developer":"dev:carol","touches":1,"totalChurn":25}]}

Q3 — Bus-factor risk sweep

Which components have been touched by exactly one developer?

MATCH (dev:Developer)-[:ASSIGNED_TO]->(:Task)-[:TOUCHES]->(c:Component)
WITH c, count(DISTINCT dev) AS busFactor, collect(DISTINCT dev.key) AS owners
WHERE busFactor = 1
RETURN c.key AS component, busFactor, owners
ORDER BY component

Nine components are owned by a single developer, e.g.:

{"component":"comp:orders/service.go","busFactor":1,"owners":["dev:bob"]}
{"component":"comp:payments/gateway.go","busFactor":1,"owners":["dev:frank"]}
{"component":"comp:platform/auth.go","busFactor":1,"owners":["dev:dave"]}

Q4 — A developer's workload

What is assigned to Alice and not yet done?

MATCH (d:Developer {key:$dev})-[a:ASSIGNED_TO]->(t:Task)
WHERE t.status <> 'done' AND a.state <> 'done'
RETURN t.key AS task, t.title AS title, t.status AS status, t.priority AS priority, a.role AS role
ORDER BY priority DESC

{"rows":[
  {"task":"task:WS-9","title":"Add product search to catalog","status":"in_progress","priority":7,"role":"author"},
  {"task":"task:WS-13","title":"Add catalog caching layer","status":"todo","priority":6,"role":"author"}]}

Q5 — What is blocked, and why (transitive chain)

MATCH path = (root:Task)-[:BLOCKS*1..]->(t:Task {key:$task})
WHERE root.status <> 'done'
RETURN [n IN nodes(path) | n.key] AS chain
ORDER BY length(path) DESC

{"rows":[
  {"chain":["task:WS-14","task:WS-10","task:WS-12"]},
  {"chain":["task:WS-10","task:WS-12"]}]}

Q6 — Most-depended-upon component

MATCH (c:Component)<-[:DEPENDS_ON]-(dependent:Component)
RETURN c.key AS component, count(dependent) AS inDegree
ORDER BY inDegree DESC
LIMIT 10

{"rows":[
  {"component":"comp:platform/config.go","inDegree":3},
  {"component":"comp:catalog/service.go","inDegree":2},
  {"component":"comp:platform/logging.go","inDegree":2}]}

Q7 — Dependency cycles

MATCH (c:Component)-[:DEPENDS_ON*1..]->(c)
RETURN DISTINCT c.key AS componentOnCycle
ORDER BY componentOnCycle

{"rows":[
  {"componentOnCycle":"comp:orders/service.go"},
  {"componentOnCycle":"comp:payments/service.go"}]}

Q8 — Component history

MATCH (dev:Developer)-[:ASSIGNED_TO]->(t:Task)-[r:TOUCHES]->(c:Component {key:$k})
RETURN dev.key AS developer, t.key AS task,
       r.change_type AS change, r.churn AS churn, r.at AS at
ORDER BY at DESC

{"rows":[
  {"developer":"dev:carol","task":"task:WS-2","change":"modify","churn":25,"at":"2026-01-15T16:30:00Z"},
  {"developer":"dev:erin","task":"task:WS-1","change":"add","churn":120,"at":"2026-01-08T16:00:00Z"}]}

Schema, constraints and query plans

At store initialisation the server declares its schema as Cypher DDL, idempotently (so re-opening a populated store is a no-op):

CREATE CONSTRAINT component_key_unique IF NOT EXISTS
       FOR (c:Component) REQUIRE c.key IS UNIQUE
CREATE INDEX IF NOT EXISTS developer_key_idx
       FOR (d:Developer) ON (d.key)

The UNIQUE constraint guarantees Component.key integrity; the secondary index accelerates Developer.key equality lookups. Because the fixture is loaded through the storage layer directly (which does not feed the engine's index change fan-out), the DDL is issued after the fixture, so each backing index is backfilled from the seeded graph; every later write goes through the engine (POST /query) and maintains the indexes incrementally.

Inspect the schema

curl -s localhost:8080/schema

{
  "labels": ["Code","Component","Developer","Module","People","Repository",
             "Sprint","Task","Team","Work","WorkflowState"],
  "relationship_types": ["ASSIGNED_TO","BLOCKS","CONTAINS","DEPENDS_ON",
                         "HAS_STATE","IN_SPRINT","MEMBER_OF","NEXT",
                         "SUBTASK_OF","TOUCHES"],
  "property_keys": ["active","at","..."],
  "indexes": [{"name":"__uniq__Component.key","type":"hash"},
              {"name":"developer_key_idx","type":"hash"}],
  "constraints": [{"name":"component_key_unique","type":"UNIQUE",
                   "label":"Component","property":"key"}]
}

The sets are sorted so the output is stable and pinnable as facts. A UNIQUE constraint's backing hash index is reported under its reserved __uniq__<Label>.<prop> name alongside the plain index.

Constraint enforcement

Re-creating an existing Component.key violates the UNIQUE constraint. The write is rejected with 409 Conflict and rolled back atomically — the graph is unchanged:

curl -s -o /dev/null -w '%{http_code}\n' localhost:8080/query -d @- <<'JSON'
{"query":"CREATE (c:Component:Code {key:'comp:platform/config.go'})"}
JSON

409

{"error":"exec: constraint violation: UNIQUE constraint on (Component).key: value \"comp:platform/config.go\" already exists","kind":"conflict"}

Explain a query plan

POST /explain shows whether the declared schema turns an equality lookup into an index seek. The Q1/Q6/Q8 filter on Component.key and Q4's filter on Developer.key are served by a NodeByIndexSeek:

curl -s localhost:8080/explain -d @- <<'JSON'
{"query":"MATCH (c:Component) WHERE c.key = $k RETURN c","params":{"k":"comp:platform/config.go"}}
JSON

{"plan":"ProduceResults\n└─ Projection\n   └─ NodeByIndexSeek\n","uses_index_seek":true}

An equality on an un-indexed property falls back to a full label scan ("uses_index_seek":false, plan contains NodeByLabelScan), which is itself evidence: the difference between the two plans is the difference between an O(1) seek and an O(N) scan.

Persistence — survives a crash

Every committed write is fsynced to the WAL before the response returns, so the data survives even a hard kill:

go run ./examples/25_software_house_api -d ./data -addr :8080 &
curl -s -XPOST localhost:8080/seed
curl -s localhost:8080/query -d @- <<'JSON'
{"query":"CREATE (d:Developer:People {key:'dev:zoe', name:'Zoe'})"}
JSON

kill -9 %1                       # crash: no graceful shutdown, no final snapshot

go run ./examples/25_software_house_api -d ./data -addr :8080 &
curl -s localhost:8080/stats     # "Developer": 7 — the seed AND dev:zoe survived

On restart, recovery replays the WAL on top of the last snapshot. A graceful SIGTERM additionally writes a fresh snapshot to shorten the next replay. Both paths are covered by cross_process_test.go.

The schema survives too. The CREATE CONSTRAINT / CREATE INDEX statements are WAL-logged writes, and the shutdown snapshot embeds the constraint set and index definitions. On open the engine is built with cypher.NewEngineWithStoreAndSchema, which re-registers both from the recovered state and re-backfills each backing index — so the UNIQUE constraint still rejects duplicates and the index seek still fires after a restart. Both cross_process_test.go restart paths assert this (constraint present in /schema, and a duplicate Component.key rejected with 409). Using the plain cypher.NewEngineWithStore here would silently drop enforcement and revert index seeks to full label scans across a restart.

The data directory holds wal (the log) and snapshot/ (manifest plus the CSR, labels, properties, mapper, and — once the schema is declared — constraints.bin and indexdefs.bin images).

Concurrency

The store is opened once and shared by all handlers. Read queries run in parallel; write queries and the seed are serialised. The store owns a sync.RWMutex (a shared hold for readers, an exclusive hold for writers) as the outermost lock because the engine's plan-building phase reads live graph structures that a concurrent write mutates — see the note in store.go. The hold is kept across the engine call, the row drain, and Result.Close. The result is snapshot-isolation reads with serialised writes; server_concurrency_test.go exercises it under -race.

Close takes the same exclusive hold before releasing the WAL, so it quiesces any in-flight write rather than closing the WAL underneath a commit that is about to fsync — which would otherwise leave that write applied in memory but lost from the WAL. After Close takes the hold it marks the store closed, so a request that arrives during shutdown is cleanly rejected with 503 instead of being admitted onto the closing WAL. close_quiesce_test.go proves the quiesce-and-reject contract under -race.

Evidence it collects

Following the examples standard, this example is both a demonstration and a source of evidence. It reports the dimensions that matter for a persistent Cypher service over a graph structure:

• Live heap and bytes-per-element — GET /stats forces a GC and reports telemetry.heap_alloc_bytes and telemetry.bytes_per_element (live heap divided by node+edge count), the structures evidence for the in-memory LPG.
• Per-endpoint latency — telemetry.last_query_ms, max_query_ms, and stats_sweep_ms (the sweep the response itself measured), plus request counters (query_count, write_count, stats_count).
• Seed/build cost — telemetry.seed_ms and the startup # seed.elapsed / # seed.node_rate telemetry lines.

When you scale the graph up (-scale-*), watch bytes_per_element settle (~460 B per element at the per-edge-property scale this example uses) and the catalogue queries' latency grow — in particular the unbounded variable-length queries (Q1's DEPENDS_ON*0.., Q7's DEPENDS_ON*1..) become expensive on a dense dependency graph, which is itself evidence worth observing.

Tests

go test ./examples/25_software_house_api/...            # short layer (~5s)
go test -race ./examples/25_software_house_api/...      # race detector

Coverage: deterministic seed and the full query catalogue (seed_test.go); the opt-in synthetic scale — zero-scale equals the bare fixture, pinned deterministic counts at a fixed seed, structural invariants, and the realism properties the queries depend on (synth_test.go); every endpoint and error path including the scaled POST /seed and the GET /stats telemetry block (server_test.go, synth_test.go); the schema surface — the GET /schema label/relationship/index/constraint facts, the 409 constraint-violation path with atomic rollback, POST /explain index-seek vs label-scan, and in-process schema durability across reopen (schema_test.go); concurrent readers/writers (server_concurrency_test.go); the Close quiesce-and-reject contract against a concurrent write (close_quiesce_test.go); in-process reopen (lifecycle_test.go); and a real process restart under both SIGTERM and kill -9, each asserting the schema is durable (cross_process_test.go). The synthetic tests assert only deterministic facts (counts, structure, presence of telemetry fields) — never volatile latency or heap values. go.uber.org/goleak guards against goroutine leaks via main_test.go.