TiDB Architecture Index for Agents

This file is a navigation index for quick subsystem discovery. Hard requirements remain in the repository root AGENTS.md.

How to Use This Index

1. Map the task to one primary subsystem.
2. Find existing tests covering the same behavior.
3. Reuse existing fixtures/testdata before creating new shapes.
4. Expand to adjacent subsystems only when cross-module effects are clear.

Core Subsystems

Planner and optimization

• pkg/planner/
• pkg/planner/core/base/
• pkg/planner/core/operator/logicalop/
• pkg/planner/core/operator/physicalop/
• Typical changes: rule matching, plan shape, cost-based choices.
• First tests to inspect:
  • pkg/planner/core/casetest/
  • pkg/planner/core/casetest/rule/testdata/

Execution and expressions

• pkg/executor/
• pkg/expression/
• Typical changes: runtime operator semantics, builtin behavior, evaluation edge cases.
• First tests to inspect:
  • package unit tests under the same path
  • SQL integration tests for user-visible behavior

Session, variables, protocol

• pkg/session/
• pkg/sessionctx/
• pkg/sessionctx/variable/
• pkg/server/
• Typical changes: session lifecycle, statement context behavior, protocol-level behavior.

DDL and metadata

• pkg/ddl/
• pkg/infoschema/
• pkg/meta/
• pkg/meta/autoid/
• Typical changes: schema evolution, metadata persistence, ID generation.

Storage and distributed execution

• pkg/kv/
• pkg/store/
• pkg/distsql/
• pkg/tablecodec/
• Typical changes: KV semantics, storage integration, distributed query paths.

Domain and statistics

• pkg/domain/
• pkg/statistics/
• Typical changes: schema/statistics lifecycle, cardinality/estimation behavior.

Parser and AST

• pkg/parser/
• Typical changes: SQL grammar, AST nodes, parser behavior.

Test Surfaces

• Unit tests: package-local tests under pkg/**.
• Integration tests:
  • inputs: tests/integrationtest/t/
  • expected outputs: tests/integrationtest/r/
• RealTiKV tests:
  • tests/realtikvtest/
  • use when behavior depends on real TiKV/PD interaction.

Practical Search Workflow

1. Start from symptom:
   • SQL keyword
   • error message
   • variable name
2. Find implementation entrypoint:
   • planner/executor/expression/session/ddl/store
3. Find existing tests around the same behavior.
4. Confirm neighboring modules only if call chain crosses boundaries.

Common Cross-Module Paths

• Planner -> Executor -> Expression for query semantics.
• Session/Variables -> Executor for user-visible runtime behavior.
• DDL -> Infoschema/Meta -> Domain for schema lifecycle.
• Store/KV/DistSQL -> Executor for distributed execution behavior.

Notes and Runbooks

• Planner notes: docs/agents/planner/rule/rule_ai_notes.md
• Notes guide: docs/agents/notes-guide.md
• Testing runbook: docs/agents/testing-flow.md
• AGENTS review guide: docs/agents/agents-review-guide.md
• Root execution contract: AGENTS.md