Scenario 04: Feature Development¶
Developer understanding existing code to add new features.
Quick Start¶
# Select Feature Development Scenario
/select 04
Understanding Existing Code¶
Finding Related Functions¶
> Find functions related to transaction handling
╭─────────────── Related Code ────────────────────────────────╮
│ │
│ Transaction Functions: │
│ │
│ Entry Points: │
│ StartTransaction() src/backend/access/transam/xact.c │
│ CommitTransaction() src/backend/access/transam/xact.c │
│ AbortTransaction() src/backend/access/transam/xact.c │
│ │
│ Support Functions: │
│ AssignTransactionId() src/backend/access/transam/xact.c │
│ GetCurrentTransactionId() src/backend/access/transam/xact.c │
│ │
│ Related Modules: │
│ src/backend/access/heap/ - Heap operations │
│ src/backend/storage/lmgr/ - Lock manager │
│ │
╰──────────────────────────────────────────────────────────────╯
Understanding Call Chains¶
> Show the call path from parser to executor
╭─────────────── Call Chain ──────────────────────────────────╮
│ │
│ Parser → Executor Flow: │
│ │
│ 1. pg_parse_query() │
│ ↓ │
│ 2. pg_analyze_and_rewrite() │
│ ↓ │
│ 3. pg_plan_queries() │
│ ↓ │
│ 4. PortalRun() │
│ ↓ │
│ 5. ExecutorStart() → ExecutorRun() → ExecutorFinish() │
│ ↓ │
│ 6. ExecProcNode() [dispatches to specific nodes] │
│ │
╰──────────────────────────────────────────────────────────────╯
Integration Points¶
Finding Extension Points¶
> Where can I add a new node type?
╭─────────────── Extension Points ────────────────────────────╮
│ │
│ Adding New Executor Node Type: │
│ │
│ 1. Define node structure in: │
│ src/include/nodes/execnodes.h │
│ │
│ 2. Implement node operations: │
│ src/backend/executor/nodeXXX.c │
│ - ExecInitXXX() │
│ - ExecXXX() │
│ - ExecEndXXX() │
│ │
│ 3. Register in dispatcher: │
│ src/backend/executor/execProcnode.c │
│ - ExecInitNode() │
│ - ExecProcNode() │
│ │
╰──────────────────────────────────────────────────────────────╯
Understanding Dependencies¶
> What modules does the buffer manager depend on?
╭─────────────── Dependencies ────────────────────────────────╮
│ │
│ Buffer Manager Dependencies: │
│ │
│ Upstream (uses): │
│ - storage/smgr (Storage manager interface) │
│ - storage/lmgr (Lock manager) │
│ - utils/memutils (Memory contexts) │
│ │
│ Downstream (used by): │
│ - access/heap (Heap access methods) │
│ - access/index (Index access methods) │
│ - executor/* (Query execution) │
│ │
│ Interfaces: │
│ - ReadBuffer() (Main read interface) │
│ - ReleaseBuffer() (Release interface) │
│ │
╰──────────────────────────────────────────────────────────────╯
Code Patterns¶
Finding Similar Implementations¶
> Show examples of error handling in executor
╭─────────────── Error Handling Patterns ─────────────────────╮
│ │
│ Common Patterns in Executor: │
│ │
│ 1. ereport with ERROR level: │
│ ereport(ERROR, │
│ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), │
│ errmsg("feature X not supported"))); │
│ │
│ 2. Exception handling with PG_TRY: │
│ PG_TRY(); │
│ { │
│ /* risky operation */ │
│ } │
│ PG_CATCH(); │
│ { │
│ /* cleanup */ │
│ PG_RE_THROW(); │
│ } │
│ PG_END_TRY(); │
│ │
╰──────────────────────────────────────────────────────────────╯
Placement Recommendations¶
> Where should I place new cache invalidation feature?
╭─────────────── Recommended Placement ─────────────────────╮
│ │
│ Subsystem: cache manager │
│ File: src/backend/utils/cache.c │
│ Near method: cache_lookup() (line 145) │
│ Confidence: 75% │
│ │
│ Related methods in this area: │
│ - cache_insert() │
│ - cache_remove() │
│ - cache_invalidate_all() │
│ │
╰────────────────────────────────────────────────────────────╯
Pattern Examples¶
> Show pattern examples for executor subsystem
╭─────────────── Pattern Examples ──────────────────────────╮
│ │
│ Examples from the target subsystem: │
│ │
│ Method | File | Pattern | CC │
│ init_executor() | execMain.c:42 | Initialization | 3 │
│ exec_scan() | execScan.c:88 | Handler | 5 │
│ get_plan_node() | execUtils.c:15| Query/lookup | 2 │
│ check_perms() | execPerms.c:7 | Validation | 4 │
│ end_executor() | execMain.c:200| Cleanup | 1 │
│ │
╰────────────────────────────────────────────────────────────╯
Example Questions¶
- “How does [feature_name] work?”
- “What functions are involved in [subsystem]?”
- “Where should I place new [feature] in [module]?”
- “Show similar implementations to [existing_feature]”
- “What’s the data flow for [operation]?”
- “Find integration points for [component]”
- “Show pattern examples for [subsystem]”
- “Recommend placement for new [feature_type]”
Related Scenarios¶
- Onboarding - Codebase exploration basics
- Architecture - Architectural understanding
- Refactoring - Code improvement