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Query Efficiency Auditor (L3 Worker)

Specialized worker auditing database query patterns for redundancy, inefficiency, and misuse.

Purpose & Scope

• Worker in ln-650 coordinator pipeline – invoked by ln-650-persistence-performance-auditor
• Audit query efficiency (Priority: HIGH)
• Check redundant fetches, batch operation misuse, caching scope problems
• Return structured findings with severity, location, effort, recommendations
• Calculate compliance score (X/10) for Query Efficiency category

Inputs (from Coordinator)

MANDATORY READ: Load shared/references/task_delegation_pattern.md#audit-coordinator--worker-contract for contextStore structure.

Receives contextStore with: tech_stack, best_practices, db_config (database type, ORM settings), codebase_root.

Domain-aware: Supports domain_mode + current_domain.

Workflow

1. Parse context from contextStore

   • Extract tech_stack, best_practices, db_config
   • Determine scan_path (same logic as ln-624)

2. Scan codebase for violations

   • All Grep/Glob patterns use scan_path
   • Trace call chains for redundant fetches (requires reading caller + callee)

3. Collect findings with severity, location, effort, recommendation

4. Calculate score using penalty algorithm

5. Return JSON result to coordinator

Audit Rules (Priority: HIGH)

1. Redundant Entity Fetch

What: Same entity fetched from DB twice in a call chain

Detection:

• Find function A that calls repo.get(id) or session.get(Model, id), then passes id (not object) to function B
• Function B also calls repo.get(id) or session.get(Model, id) for the same entity
• Common pattern: acquire_next_pending() returns job, but _process_job(job_id) re-fetches it

Detection patterns (Python/SQLAlchemy):

• Grep for repo.*get_by_id|session\.get\(|session\.query.*filter.*id in service/handler files
• Trace: if function receives entity_id: int/UUID AND internally does repo.get(entity_id), check if caller already has entity object
• Check expire_on_commit setting: if False, objects remain valid after commit

Severity:

• HIGH: Redundant fetch in API request handler (adds latency per request)
• MEDIUM: Redundant fetch in background job (less critical)

Recommendation: Pass entity object instead of ID, or remove second fetch when expire_on_commit=False

Effort: S (change signature to accept object instead of ID)

2. N-UPDATE/DELETE Loop

What: Loop of individual UPDATE/DELETE operations instead of single batch query

Detection:

• Pattern: for item in items: await repo.update(item.id, ...) or for item in items: await repo.delete(item.id)
• Pattern: for item in items: session.execute(update(Model).where(...))

Detection patterns:

• Grep for for .* in .*: followed by repo\.(update|delete|reset|save|mark_) within 1-3 lines
• Grep for for .* in .*: followed by session\.execute\(.*update\( within 1-3 lines

Severity:

• HIGH: Loop over >10 items (N separate round-trips to DB)
• MEDIUM: Loop over <=10 items

Recommendation: Replace with single UPDATE ... WHERE id IN (...) or session.execute(update(Model).where(Model.id.in_(ids)))

Effort: M (rewrite query + test)

3. Unnecessary Resolve

What: Re-resolving a value from DB when it is already available in the caller’s scope

Detection:

• Method receives profile_id and resolves engine from it, but caller already determined engine
• Method receives lang_code and looks up dialect_id, but caller already has both lang and dialect
• Pattern: function receives X_id, does get(X_id), extracts .field, when caller already has field

Severity:

• MEDIUM: Extra DB query per invocation, especially in high-frequency paths

Recommendation: Split method into two variants: with_known_value(value, ...) and resolving_value(id, ...); or pass resolved value directly

Effort: S-M (refactor signature, update callers)

4. Over-Fetching

What: Loading full ORM model when only few fields are needed

Detection:

• session.query(Model) or select(Model) without .options(load_only(...)) for models with >10 columns
• Especially in list/search endpoints that return many rows
• Pattern: loading full entity but only using 2-3 fields

Severity:

• MEDIUM: Large models (>15 columns) in list endpoints
• LOW: Small models (<10 columns) or single-entity endpoints

Recommendation: Use load_only(), defer(), or raw select(Model.col1, Model.col2) for list queries

Effort: S (add load_only to query)

5. Missing Bulk Operations

What: Sequential INSERT/DELETE/UPDATE instead of bulk operations

Detection:

• for item in items: session.add(item) instead of session.add_all(items)
• for item in items: session.delete(item) instead of bulk delete
• Pattern: loop with single INSERT per iteration

Severity:

• MEDIUM: Any sequential add/delete in loop (missed batch optimization)

Recommendation: Use session.add_all(), session.execute(insert(Model).values(list_of_dicts)), bulk_save_objects()

Effort: S (replace loop with bulk call)

6. Wrong Caching Scope

What: Request-scoped cache for data that rarely changes (should be app-scoped)

Detection:

• Service registered as request-scoped (e.g., via FastAPI Depends()) with internal cache (_cache dict, _loaded flag)
• Cache populated by expensive query (JOINs, aggregations) per each request
• Data TTL >> request duration (e.g., engine configurations, language lists, feature flags)

Detection patterns:

• Find classes with _cache, _loaded, _initialized attributes
• Check if class is created per-request (via DI registration scope)
• Compare: data change frequency vs cache lifetime

Severity:

• HIGH: Expensive query (JOINs, subqueries) cached only per-request
• MEDIUM: Simple query cached per-request

Recommendation: Move cache to app-scoped service (singleton), add TTL-based invalidation, or use CacheService with configurable TTL

Effort: M (change DI scope, add TTL logic)

Scoring Algorithm

MANDATORY READ: Load shared/references/audit_scoring.md for unified scoring formula.

Output Format

Return JSON to coordinator:

{
  "category": "Query Efficiency",
  "score": 6,
  "total_issues": 8,
  "critical": 0,
  "high": 3,
  "medium": 4,
  "low": 1,
  "findings": [
    {
      "severity": "HIGH",
      "location": "app/infrastructure/messaging/job_processor.py:434",
      "issue": "Redundant entity fetch: job re-fetched by ID after acquire_next_pending already returned it",
      "principle": "Query Efficiency / DRY Data Access",
      "recommendation": "Pass job object to _process_job instead of job_id",
      "effort": "S"
    }
  ]
}

Critical Rules

• Do not auto-fix: Report only
• Trace call chains: Rules 1 and 3 require reading both caller and callee
• ORM-aware: Check expire_on_commit, autoflush, session scope before flagging redundant fetches
• Context-aware: Small datasets or infrequent operations may justify simpler code
• Exclude tests: Do not flag test fixtures or setup code

Definition of Done

• contextStore parsed (tech_stack, db_config, ORM settings)
• scan_path determined (domain path or codebase root)
• All 6 checks completed:
  • redundant fetch, N-UPDATE loop, unnecessary resolve, over-fetching, bulk ops, caching scope
• Findings collected with severity, location, effort, recommendation
• Score calculated
• JSON returned to coordinator

Reference Files

• Audit scoring formula: shared/references/audit_scoring.md
• Audit output schema: shared/references/audit_output_schema.md

Version: 1.0.0 Last Updated: 2026-02-04