# Code Complete vs Designing Data-Intensive Applications

Status: reviewed
Research basis: mini-only

Verdict: ✅ Complementary

Conflict: 10%
Overlap: 35%
Complementarity: 80%

## Loading Decision

Use together when the task changes state, events, schemas, queues, projections, caches, consistency, or ownership while also needing Code Complete pressure.

## Book A Pressure

- Code Complete should drive tasks where defect reduction, data clarity, defensive checks, evidence-based debugging, and reviewability dominate.
- Evidence: `code-complete/code-complete.mini.md` lines 3-5: applies to implementation, change, review, debugging, refactoring, and tuning of production code.

## Book B Pressure

- Designing Data-Intensive Applications should drive tasks where source of truth, consistency, durability, replay, schemas, replication, partitioning, or distributed failure dominate.
- Evidence: `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 3-5: applies where correctness depends on data ownership, consistency, durability, replication, partitioning, schema evolution, event flow, replay, or derived data.

## Complementary Forces

- Claim: Code Complete contributes defect-reduction, data-clarity, defensive-check, evidence-based-debugging, and reviewability pressure; Designing Data-Intensive Applications contributes source-of-truth, consistency, replay, schema-evolution, partitioning, and distributed-failure pressure. Together they are useful only where both scopes are active.
- Evidence:
  - `code-complete/code-complete.mini.md` lines 13-31: requires construction prerequisites, small validated slices, clear routines/data/control flow, validated data-driven logic, trust-boundary validation, explicit error semantics, cohesive modules, complexity management, small increments, evidence-based debugging, measured tuning, and useful tooling/comments.
  - `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 34-42: fires on write paths, derived data, schema/API/event changes, retries/jobs/queues/replay, replica reads, partitioning, isolation choices, clock/lock/consensus assumptions, and data-intensive review risks.

## Overlap

- Claim: They overlap where both affect boundaries, explicit responsibilities, tests, coupling reduction, and avoiding hidden assumptions; the overlap score reflects how often an agent would receive similar pressure from both.
- Evidence:
  - `code-complete/code-complete.mini.md` lines 51-56: checks requirements, architecture fit, construction approach, readable code structure, deliberate inputs/errors/invariants, inspectable flow, evidence-based validation, and reviewable change size.
  - `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 46-55: checks source of truth, consistency/durability/staleness/conflicts, retry/replay/reordering, safe evolution, workload-matched storage, invariant-protecting isolation, rebuildable streams/projections, ownership-aligned services, observability, and no exactly-once wishful thinking.

## Conflicts

- Claim: The tension is over-modeling: the non-data rule set may improve structure, but DDIA requires explicit data semantics before abstractions hide source-of-truth or failure behavior.
- Evidence:
  - `code-complete/code-complete.mini.md` lines 7-9: corrects accidental construction by choosing lower defect risk and easier reasoning over clever idioms.
  - `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 34-42: fires on write paths, derived data, schema/API/event changes, retries/jobs/queues/replay, replica reads, partitioning, isolation choices, clock/lock/consensus assumptions, and data-intensive review risks.

## Use Together When

- Use together when the other design concern changes source of truth, consistency, schema evolution, event flow, replay, derived data, partitions, or ownership boundaries.

## Prefer One When

- Prefer DDIA when consistency, schemas, replay, ordering, source of truth, or distributed data failure is the hard part; prefer the other book when those data semantics are not in scope.

## Source Basis

- `code-complete/code-complete.mini.md` lines 3-5: applies to implementation, change, review, debugging, refactoring, and tuning of production code.
- `code-complete/code-complete.mini.md` lines 7-9: corrects accidental construction by choosing lower defect risk and easier reasoning over clever idioms.
- `code-complete/code-complete.mini.md` lines 13-31: requires construction prerequisites, small validated slices, clear routines/data/control flow, validated data-driven logic, trust-boundary validation, explicit error semantics, cohesive modules, complexity management, small increments, evidence-based debugging, measured tuning, and useful tooling/comments.
- `code-complete/code-complete.mini.md` lines 51-56: checks requirements, architecture fit, construction approach, readable code structure, deliberate inputs/errors/invariants, inspectable flow, evidence-based validation, and reviewable change size.
- `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 3-5: applies where correctness depends on data ownership, consistency, durability, replication, partitioning, schema evolution, event flow, replay, or derived data.
- `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 7-9: corrects local-happy-path thinking about writes, reads, queues, caches, replicas, clocks, and downstream side effects.
- `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 34-42: fires on write paths, derived data, schema/API/event changes, retries/jobs/queues/replay, replica reads, partitioning, isolation choices, clock/lock/consensus assumptions, and data-intensive review risks.
- `designing-data-intensive-applications/designing-data-intensive-applications.mini.md` lines 46-55: checks source of truth, consistency/durability/staleness/conflicts, retry/replay/reordering, safe evolution, workload-matched storage, invariant-protecting isolation, rebuildable streams/projections, ownership-aligned services, observability, and no exactly-once wishful thinking.

## Review Notes

- External context was not used as decisive evidence for Code Complete vs Designing Data-Intensive Applications; the verdict is based on the cited local `mini` line ranges.
