# MRRC Project History

This directory contains the archived design documents, code reviews, implementation notes, and project decisions that shaped the MRRC library. These documents provide context for how the project evolved and why certain architectural decisions were made.

## Organization

Documents are grouped by category to show how different work areas developed and relate to each other.

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## 🔍 Code Review & Audits (December 2025)

Comprehensive code review audit suite (Epic mrrc-aw5). All audits completed with overall assessment: **EXCELLENT**, 0 critical issues.

### Overview & Summary
- **[CODE_REVIEW_SUMMARY.md](./CODE_REVIEW_SUMMARY.md)** - Executive summary of all 10 audits, key findings, metrics
- **[CODE_REVIEW_NOTES.md](./CODE_REVIEW_NOTES.md)** - Detailed findings from individual audits

### Specialized Audits (10 comprehensive reviews)

**API & Consistency**:
- **[API_CONSISTENCY_AUDIT.md](./API_CONSISTENCY_AUDIT.md)** - Public API naming, patterns, and consistency across modules
- **[PYMARC_API_AUDIT.md](./PYMARC_API_AUDIT.md)** - Compatibility with pymarc API surface

**Core Architecture**:
- **[CORE_DUPLICATION_AUDIT.md](./CORE_DUPLICATION_AUDIT.md)** - Record, Field, and common implementation analysis
- **[RUST_IDIOMATICITY_AUDIT.md](./RUST_IDIOMATICITY_AUDIT.md)** - Style, patterns, and Rust best practices

**Features & Implementation**:
- **[FORMAT_CONVERSION_AUDIT.md](./FORMAT_CONVERSION_AUDIT.md)** - JSON, XML, MARCJSON, CSV, Dublin Core, MODS converters
- **[ENCODING_SPECIALIZED_AUDIT.md](./ENCODING_SPECIALIZED_AUDIT.md)** - MARC-8, UTF-8, and character encoding support
- **[IO_MODULES_AUDIT.md](./IO_MODULES_AUDIT.md)** - Reader/Writer robustness and error handling
- **[QUERY_VALIDATION_AUDIT.md](./QUERY_VALIDATION_AUDIT.md)** - Field query DSL and validation framework

**Project & Testing**:
- **[PROJECT_STRUCTURE_AUDIT.md](./PROJECT_STRUCTURE_AUDIT.md)** - File organization, module layout, dependencies
- **[TEST_ORGANIZATION_AUDIT.md](./TEST_ORGANIZATION_AUDIT.md)** - Test structure, coverage, and organization

---

## 🏗️ Major Design Work

### API Refactoring (Epic mrrc-c4v)

Comprehensive refactoring to reduce code duplication across Record, AuthorityRecord, and HoldingsRecord.

- **[api-refactor-proposal.md](./api-refactor-proposal.md)** - Original proposal for refactoring
- **[API_REFACTOR_COMPLETED.md](./API_REFACTOR_COMPLETED.md)** - Completion status and results
  - Introduced `MarcRecord` trait for common operations
  - Created `GenericRecordBuilder<T>` unified builder
  - Implemented `FieldCollection` and `RecordHelpers` traits
  - Eliminated ~300 LOC of duplication
  - Zero breaking changes, full backward compatibility

### Field Query DSL (Epic mrrc-08k, mrrc-69n)

Domain-specific query patterns for complex field selection.

- **[FIELD_QUERY_DSL.md](./FIELD_QUERY_DSL.md)** - Design and specification
- **[FIELD_QUERY_DSL_COMPLETED.md](./FIELD_QUERY_DSL_COMPLETED.md)** - Completion summary
  - Phase 1: FieldQuery builder, TagRangeQuery, indicators, subfields
  - Phase 2: Regex subfield matching, value filtering, convenience methods
  - Phase 3: Linked field navigation (880), authority helpers, format traits
  - 97+ specialized tests + 282 library tests

### Authority & Holdings Records (Epic mrrc-fzy)

Specialized support for MARC Authority and Holdings records.

- **[AUTHORITY_RECORD_DESIGN.md](./AUTHORITY_RECORD_DESIGN.md)** - Design and architecture
  - Authority record structure with heading types (1XX) and tracings (4XX/5XX)
  - Holdings record implementation with location and call number support
  - Readers, writers, and comprehensive test coverage

### Field Insertion Order Preservation (mrrc-e1l)

Replaced BTreeMap with IndexMap to preserve field insertion order for round-trip fidelity.

- **[FIELD_INSERTION_ORDER_PRESERVATION.md](./FIELD_INSERTION_ORDER_PRESERVATION.md)** - Design, implementation, and completion summary
  - Replaced `BTreeMap` with `IndexMap` in Record, AuthorityRecord, HoldingsRecord
  - Enables round-trip fidelity: serialization/deserialization preserves original field order
  - Required for binary format evaluation (Protobuf, Avro, etc.)
  - Trade-off: ~17-22% benchmark regression (acceptable for fidelity requirement)

---

## 🔗 Python Wrapper & GIL Release

### Python Wrapper Strategy (Epic mrrc-d3s)

Strategy for creating a PyO3-based Python extension with near 100% API compatibility with pymarc.

- **[PYTHON_WRAPPER_PROPOSAL.md](./PYTHON_WRAPPER_PROPOSAL.md)** - Original proposal
- **[PYTHON_WRAPPER_STRATEGIES.md](./PYTHON_WRAPPER_STRATEGIES.md)** - Different implementation approaches
- **[PYTHON_WRAPPER_DECISIONS.md](./PYTHON_WRAPPER_DECISIONS.md)** - Final architectural decisions
- **[PYTHON_WRAPPER_REVIEW.md](./PYTHON_WRAPPER_REVIEW.md)** - Design review and feedback

### GIL Release Implementation (Epic mrrc-gyk)

Enabling true multi-core parallelism through GIL release during record parsing.

**Planning & Design**:
- **[GIL_RELEASE_STRATEGY.md](./GIL_RELEASE_STRATEGY.md)** - Initial strategy
- **[GIL_RELEASE_STRATEGY_REVISED.md](./GIL_RELEASE_STRATEGY_REVISED.md)** - Revised approach
- **[GIL_RELEASE_INVESTIGATION_ADDENDUM.md](./GIL_RELEASE_INVESTIGATION_ADDENDUM.md)** - Investigation findings and fixes
- **[GIL_RELEASE_CURRENT_PLAN.md](./GIL_RELEASE_CURRENT_PLAN.md)** - Current implementation status

**Hybrid Implementation Plan** (Phase-based approach):
- **[GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN.md](./GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN.md)** - Main hybrid plan
- **[GIL_RELEASE_HYBRID_PLAN.md](./GIL_RELEASE_HYBRID_PLAN.md)** - Alternative hybrid approach
- **[GIL_RELEASE_HYBRID_PLAN_REVIEW.md](./GIL_RELEASE_HYBRID_PLAN_REVIEW.md)** - Review of hybrid plan
- **[GIL_RELEASE_HYBRID_PLAN_REVIEW_ASSESSMENT.md](./GIL_RELEASE_HYBRID_PLAN_REVIEW_ASSESSMENT.md)** - Assessment summary
- **[GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN_REVIEW.md](./GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN_REVIEW.md)** - Detailed review
- **[GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN_REVISIONS.md](./GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN_REVISIONS.md)** - Revision notes
- **[GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN_WITH_BEADS_MAPPING.md](./GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN_WITH_BEADS_MAPPING.md)** - Mapped to issue tracking

**Implementation Plans**:
- **[GIL_RELEASE_IMPLEMENTATION_PLAN_FINAL.md](./GIL_RELEASE_IMPLEMENTATION_PLAN_FINAL.md)** - Final implementation plan
- **[GIL_RELEASE_IMPLEMENTATION_REVIEW.md](./GIL_RELEASE_IMPLEMENTATION_REVIEW.md)** - Implementation review

**Execution & Completion**:
- **[GIL_RELEASE_PUNCHLIST.md](./GIL_RELEASE_PUNCHLIST.md)** - Tasks to complete
- **[GIL_RELEASE_REVIEW.md](./GIL_RELEASE_REVIEW.md)** - Final review
- **[GIL_RELEASE_PROPOSAL_REVIEW.md](./GIL_RELEASE_PROPOSAL_REVIEW.md)** - Proposal review

**Status**: ✅ Completed. GIL is released during record parsing in Phase 2, enabling:
- 2.0x speedup on 2 threads
- 3.74x speedup on 4 threads
- Linear scaling with CPU core count

---

## 📊 Parallel Processing & Benchmarking

### Parallel Benchmarking (Phases C, D, E, F)

Development of the comprehensive benchmarking suite.

- **[PARALLEL_BENCHMARKING_FEASIBILITY.md](./PARALLEL_BENCHMARKING_FEASIBILITY.md)** - Phase B feasibility study
- **[PARALLEL_BENCHMARKING_SUMMARY.md](./PARALLEL_BENCHMARKING_SUMMARY.md)** - Summary of parallel benchmarking work

### Phase 3 Implementation (Epic mrrc-jyk)

Threading support and parallel benchmarking infrastructure.

- **[PHASE3_IMPLEMENTATION_PLAN.md](./PHASE3_IMPLEMENTATION_PLAN.md)** - Phase 3 roadmap and tasks

---

## 📋 Project Planning & Integration

### Beads (Issue Tracking) Integration

Integration of the project with Beads issue tracking system.

- **[BEADS_ACTION_SUMMARY.md](./BEADS_ACTION_SUMMARY.md)** - Action items and summary
- **[BEADS_COVERAGE_ANALYSIS.md](./BEADS_COVERAGE_ANALYSIS.md)** - Coverage analysis of issues
- **[BEADS_IMPLEMENTATION_CHECKLIST.md](./BEADS_IMPLEMENTATION_CHECKLIST.md)** - Implementation tasks
- **[README_BEADS_INTEGRATION.md](./README_BEADS_INTEGRATION.md)** - Beads integration documentation

### Planning & Reviews

- **[PLAN_REVIEW_INDEX.md](./PLAN_REVIEW_INDEX.md)** - Index of all plan reviews

### Session Management

- **[SESSION_CLEANUP_SUMMARY.md](./SESSION_CLEANUP_SUMMARY.md)** - Session cleanup summary
- **[SESSION_HANDOFF.md](./SESSION_HANDOFF.md)** - Session handoff notes

---

## 🎯 Original Project Plan

- **[PYMARC_RUST_PORT_PLAN.md](./PYMARC_RUST_PORT_PLAN.md)** - Original project plan and porting strategy
  - Overview of the MARC standard and pymarc library
  - Rust port vision and design goals
  - Technical decisions and rationale
  - Module-by-module porting plan

---

## Key Insights from History

### Design Patterns Established

1. **Three-Tier Record Types**: Bibliographic, Authority, Holdings sharing `MarcRecord` trait
2. **Three-Phase GIL Management**: Hold → Release (parsing) → Re-acquire (conversion)
3. **Multiple Reader Backends**: RustFile, PythonFile, Cursor with optimal performance paths
4. **Query DSL**: Flexible field selection with support for indicators, subfields, patterns
5. **Format Flexibility**: Multiple serialization formats with round-trip testing

### Code Quality Metrics (December 2025)

- **10 comprehensive audits** completed
- **Overall assessment**: EXCELLENT (0 critical issues)
- **API consistency**: Strong (minor naming opportunities for improvement)
- **Rust idiomaticity**: Excellent (follows best practices)
- **Test coverage**: Good (239 tests, 97+ for query DSL alone)
- **Duplication eliminated**: ~300 LOC through trait refactoring

### Performance Achievements

- **Single-threaded**: ~300,000 rec/s (~4x faster than pymarc)
- **Multi-threaded (2)**: ~2x speedup (linear on 2 cores)
- **Multi-threaded (4)**: ~3-4x speedup (good scaling on 4 cores)
- **Memory**: ~4 KB per record, proper streaming support

### Key Decisions Made

1. **Hybrid Python Wrapper**: Supports multiple input types (file paths, file objects, bytes) with optimal GIL management per backend
2. **GIL Release During Parsing**: Phase 2 (CPU-intensive) releases GIL, enabling true parallelism
3. **SmallVec Optimization**: 4 KB inline buffer handles 85-90% of records without allocation
4. **Batch Reader**: Reduces GIL acquisitions by 99% for Python file objects
5. **Not Send/Sync by Design**: Forces correct threading pattern (one reader per thread)

---

## Document Index by Topic

### Python Wrapper Implementation
- PYTHON_WRAPPER_PROPOSAL.md
- PYTHON_WRAPPER_STRATEGIES.md
- PYTHON_WRAPPER_DECISIONS.md
- PYTHON_WRAPPER_REVIEW.md

### GIL Release
- GIL_RELEASE_STRATEGY.md → GIL_RELEASE_STRATEGY_REVISED.md
- GIL_RELEASE_HYBRID_IMPLEMENTATION_PLAN.md (and variants)
- GIL_RELEASE_IMPLEMENTATION_PLAN_FINAL.md

### API Design
- api-refactor-proposal.md → API_REFACTOR_COMPLETED.md
- FIELD_QUERY_DSL.md → FIELD_QUERY_DSL_COMPLETED.md
- AUTHORITY_RECORD_DESIGN.md

### Code Quality
- CODE_REVIEW_SUMMARY.md (overview)
- CODE_REVIEW_NOTES.md (detailed findings)
- 10 specialized audits (API, Rust, Encoding, etc.)

### Benchmarking
- PARALLEL_BENCHMARKING_FEASIBILITY.md
- PARALLEL_BENCHMARKING_SUMMARY.md
- PHASE3_IMPLEMENTATION_PLAN.md

### Project Setup
- PYMARC_RUST_PORT_PLAN.md (original)
- BEADS_* (issue tracking integration)
- SESSION_* (session management)

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## Reading Recommendations

**For New Contributors**:
1. Start with PYMARC_RUST_PORT_PLAN.md (context)
2. Read CODE_REVIEW_SUMMARY.md (current state)
3. Check specific audit for your area (API, Rust, Encoding, etc.)

**For Maintainers**:
1. CODE_REVIEW_SUMMARY.md (overview)
2. GIL_RELEASE_INVESTIGATION_ADDENDUM.md (current implementation)
3. API_REFACTOR_COMPLETED.md (trait structure)

**For Users Wondering About Design Decisions**:
1. Find the relevant design proposal (e.g., PYTHON_WRAPPER_PROPOSAL.md)
2. Read the corresponding review document
3. Check the completion status document

---

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## 📦 Format Research & Evaluation (January 2026)

Comprehensive evaluation of serialization formats for MARC record interchange.

### Overview
- **[format-research/README.md](./format-research/README.md)** - Overview of format evaluation project
- **[format-research/EVALUATION_FRAMEWORK.md](./format-research/EVALUATION_FRAMEWORK.md)** - Evaluation methodology
- **[format-research/COMPARISON_MATRIX.md](./format-research/COMPARISON_MATRIX.md)** - Side-by-side format comparison
- **[format-research/FORMAT_SUPPORT_STRATEGY.md](./format-research/FORMAT_SUPPORT_STRATEGY.md)** - Final implementation strategy

### Baseline
- **[format-research/BASELINE_ISO2709.md](./format-research/BASELINE_ISO2709.md)** - ISO 2709 baseline measurements

### Format Evaluations
- **[format-research/EVALUATION_PROTOBUF.md](./format-research/EVALUATION_PROTOBUF.md)** - Protocol Buffers (Tier 1)
- **[format-research/EVALUATION_ARROW.md](./format-research/EVALUATION_ARROW.md)** - Apache Arrow (Tier 2)
- **[format-research/EVALUATION_FLATBUFFERS.md](./format-research/EVALUATION_FLATBUFFERS.md)** - FlatBuffers (Tier 2)
- **[format-research/EVALUATION_MESSAGEPACK.md](./format-research/EVALUATION_MESSAGEPACK.md)** - MessagePack (Tier 2)
- **[format-research/EVALUATION_CBOR.md](./format-research/EVALUATION_CBOR.md)** - CBOR (Tier 3)
- **[format-research/EVALUATION_AVRO.md](./format-research/EVALUATION_AVRO.md)** - Apache Avro (Tier 3)
- **[format-research/EVALUATION_PARQUET.md](./format-research/EVALUATION_PARQUET.md)** - Parquet analysis
- **[format-research/EVALUATION_POLARS_ARROW_DUCKDB.md](./format-research/EVALUATION_POLARS_ARROW_DUCKDB.md)** - Analytics integration

### Supporting Documents
- **[format-research/FIDELITY_TEST_SET.md](./format-research/FIDELITY_TEST_SET.md)** - Test data for round-trip validation
- **[format-research/TEMPLATE_evaluation.md](./format-research/TEMPLATE_evaluation.md)** - Template for future evaluations

**Status**: ✅ Completed. Implemented Tier 1 (ISO 2709, Protobuf), Tier 2 (Arrow, FlatBuffers, MessagePack), and framework for Tier 3 (CBOR, Avro).

---

## 📅 Versioning Evaluation (January 2026)

Evaluation of calendar versioning (CalVer) vs semantic versioning (SemVer) for the project.

- **[CALENDAR_VERSIONING_PROPOSAL.md](./CALENDAR_VERSIONING_PROPOSAL.md)** - Comprehensive CalVer evaluation
  - Compared YYYY.MM.PATCH CalVer against SemVer (current)
  - Analyzed release cadence, ecosystem fit, and user expectations
  - Evaluated migration paths and implementation requirements
  - Risk assessment for both approaches

**Decision**: Stay with Semantic Versioning. SemVer better fits Rust ecosystem norms, provides clear API stability signaling, and aligns with crates.io expectations.

---

## 🐍 Python Version Support (February 2026)

Update to Python version support matrix.

- **[python-313-314-support.md](./python-313-314-support.md)** - Python 3.13/3.14 support plan
  - Dropped Python 3.9 (EOL October 2025)
  - Added Python 3.13 support (stable October 2024)
  - Added Python 3.14 support (stable October 2025)
  - Updated minimum version from 3.9 to 3.10
  - CI/CD, documentation, and configuration updates
  - Benchmark comparison showed no significant regressions

**Status**: ✅ Completed. PR #9 merged with all CI checks passing.

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## 📚 Documentation Reorganization (January 2026)

Complete restructure of project documentation using Material for MkDocs.

- **[DOCS-REORG.md](./DOCS-REORG.md)** - Documentation reorganization plan
  - Migrated from 900-line README to structured documentation site
  - Created Getting Started, Tutorials, Guides, Reference, Examples sections
  - Implemented Material for MkDocs with light/dark theme toggle
  - Added search, navigation tabs, and mobile-responsive layout
  - Established style guidelines for factual, non-promotional documentation

**Status**: ✅ Completed. Documentation site live at https://dchud.github.io/mrrc/

---

**Last Updated**: 2026-02-03
**Archive Period**: September 2025 - January 2026
**Status**: Project in active maintenance, all major features complete
