# Performance Audit Report

**Branch**: feature/findall-pagination
**Base**: main
**Date**: 2025-12-18 20:47
**Files Analyzed**: 10
**Lines Changed**: ~450 (additions + modifications)

---

## Summary

This branch introduces pagination support for `findAll()` methods in both `TaskRepository` and `DependencyRepository`. The changes are **performance-positive** overall - they add safeguards against unbounded queries that could cause memory exhaustion in production.

---

## Category 1: Performance Issues in Your Changes (BLOCKING if Severe)

### HIGH

**Statement preparation inside method** - `/workspace/delegate/src/implementations/task-repository.ts:221-224`

- **Problem**: New `findAll()` method creates a prepared statement on every call instead of reusing a pre-compiled statement
- **Impact**: SQLite statement preparation has overhead (~0.1-0.5ms per call). For frequent pagination queries, this adds up.
- **Code** (ADDED in this branch):
  ```typescript
  async findAll(limit?: number, offset?: number): Promise<Result<readonly Task[]>> {
    return tryCatchAsync(
      async () => {
        const effectiveLimit = limit ?? SQLiteTaskRepository.DEFAULT_LIMIT;
        const effectiveOffset = offset ?? 0;

        const stmt = this.db.prepare(`
          SELECT * FROM tasks ORDER BY created_at DESC LIMIT ? OFFSET ?
        `);  // <-- Prepared on every call
        const rows = stmt.all(effectiveLimit, effectiveOffset) as TaskRow[];
        return rows.map(row => this.rowToTask(row));
      },
      ...
    );
  }
  ```
- **Fix**: Pre-compile the statement in the constructor like other statements:
  ```typescript
  // In constructor:
  this.findAllPaginatedStmt = this.db.prepare(`
    SELECT * FROM tasks ORDER BY created_at DESC LIMIT ? OFFSET ?
  `);

  // In method:
  async findAll(limit?: number, offset?: number): Promise<Result<readonly Task[]>> {
    return tryCatchAsync(
      async () => {
        const effectiveLimit = limit ?? SQLiteTaskRepository.DEFAULT_LIMIT;
        const effectiveOffset = offset ?? 0;
        const rows = this.findAllPaginatedStmt.all(effectiveLimit, effectiveOffset) as TaskRow[];
        return rows.map(row => this.rowToTask(row));
      },
      ...
    );
  }
  ```
- **Expected improvement**: ~0.1-0.5ms per call (eliminates statement compilation overhead)

---

### HIGH

**Statement preparation inside method** - `/workspace/delegate/src/implementations/dependency-repository.ts:513-516`

- **Problem**: Same issue as above - `findAll()` in DependencyRepository creates a prepared statement on every call
- **Impact**: Same overhead pattern - statement preparation cost on every paginated query
- **Code** (ADDED in this branch):
  ```typescript
  async findAll(limit?: number, offset?: number): Promise<Result<readonly TaskDependency[]>> {
    return tryCatchAsync(
      async () => {
        const effectiveLimit = limit ?? SQLiteDependencyRepository.DEFAULT_LIMIT;
        const effectiveOffset = offset ?? 0;

        const stmt = this.db.prepare(`
          SELECT * FROM task_dependencies ORDER BY created_at DESC LIMIT ? OFFSET ?
        `);  // <-- Prepared on every call
        const rows = stmt.all(effectiveLimit, effectiveOffset) as DependencyRow[];
        return rows.map(row => this.rowToDependency(row));
      },
      ...
    );
  }
  ```
- **Fix**: Pre-compile the statement in the constructor
- **Expected improvement**: ~0.1-0.5ms per call

---

### MEDIUM

**Missing index for OFFSET pagination** - `/workspace/delegate/src/implementations/task-repository.ts:222`

- **Problem**: `ORDER BY created_at DESC LIMIT ? OFFSET ?` with large offsets becomes O(n) because SQLite must skip all offset rows
- **Impact**: For offset=10000, SQLite reads and discards 10000 rows before returning results. This scales linearly with offset.
- **Context**: The `idx_tasks_created_at` index exists but OFFSET-based pagination fundamentally scans discarded rows
- **Mitigation already in place**: Default limit of 100 mitigates this for typical use cases
- **Recommendation**: Document this limitation. For large datasets, consider keyset pagination as a future enhancement:
  ```typescript
  // Keyset pagination (cursor-based) would be:
  // SELECT * FROM tasks WHERE created_at < ? ORDER BY created_at DESC LIMIT ?
  // This uses the index efficiently regardless of "offset"
  ```
- **Expected improvement**: Not urgent - current approach is acceptable for expected dataset sizes (<10K tasks)

---

## Category 2: Performance Issues in Code You Touched (Should Optimize)

### MEDIUM

**findByStatus() lacks pagination** - `/workspace/delegate/src/implementations/task-repository.ts:251-259`

- **Problem**: You added pagination to `findAll()` but `findByStatus()` remains unbounded
- **Context**: This method was not modified in this PR but is in the same file and has the same unbounded query risk
- **Code** (pre-existing, not modified):
  ```typescript
  async findByStatus(status: string): Promise<Result<readonly Task[]>> {
    return tryCatchAsync(
      async () => {
        const rows = this.findByStatusStmt.all(status) as TaskRow[];
        return rows.map(row => this.rowToTask(row));
      },
      ...
    );
  }
  ```
- **Recommendation**: Consider adding pagination for consistency:
  ```typescript
  async findByStatus(status: string, limit?: number, offset?: number): Promise<Result<readonly Task[]>>
  ```
- **Impact**: Could cause memory issues if many tasks are in same status (e.g., thousands of completed tasks)

---

## Category 3: Pre-existing Performance Issues (Not Blocking)

### MEDIUM

**Zod validation on every row** - `/workspace/delegate/src/implementations/task-repository.ts:307`

- **Problem**: `TaskRowSchema.parse(row)` validates every row from database
- **Context**: Pre-existing code, not modified in this PR
- **Impact**: Zod parsing adds ~0.5-1ms per 100 rows. For large result sets, this is noticeable.
- **Trade-off**: This is intentional for data integrity (catching database corruption)
- **Recommendation**: Keep as-is for correctness. If performance becomes critical, consider:
  - Using `safeParse` only in debug mode
  - Caching validated schemas
- **Status**: Informational only - the correctness benefit outweighs the performance cost

---

### LOW

**Transaction wrapper in test doubles** - `/workspace/delegate/tests/fixtures/test-doubles.ts:341`

- **Problem**: `TestTaskRepository.transaction()` just executes the function without any transaction semantics
- **Context**: Pre-existing, modified in this PR to add pagination methods
- **Impact**: None in tests (this is correct test double behavior)
- **Status**: Informational only - test doubles don't need real transactions

---

## Positive Performance Patterns in This PR

### GOOD: Default pagination limit of 100

```typescript
private static readonly DEFAULT_LIMIT = 100;
```

This prevents unbounded queries from accidentally loading thousands of records into memory.

### GOOD: Explicit `findAllUnbounded()` method

The architecture decision to separate unbounded queries into a clearly-named method is excellent:
- Forces developers to consciously choose unbounded queries
- Makes code review easier to spot potential issues
- Documentation explains when to use each method

### GOOD: count() method for pagination UI

```typescript
async count(): Promise<Result<number>> {
  return tryCatchAsync(
    async () => {
      const result = this.countStmt.get() as { count: number };
      return result.count;
    },
    ...
  );
}
```

This uses `SELECT COUNT(*)` which is O(1) with SQLite's internal row count optimization for simple counts.

### GOOD: Existing indexes support the queries

The schema has appropriate indexes:
- `idx_tasks_created_at` - supports ORDER BY created_at DESC
- `idx_task_dependencies_task_id` - supports dependency lookups
- `idx_tasks_status` - supports findByStatus queries

---

## Summary

**Your Changes:**
- HIGH: 2 (statement preparation in methods - SHOULD FIX)
- MEDIUM: 1 (OFFSET pagination limitation - DOCUMENT)

**Code You Touched:**
- MEDIUM: 1 (findByStatus lacks pagination - CONSIDER)

**Pre-existing:**
- MEDIUM: 1 (Zod validation overhead - INFORMATIONAL)
- LOW: 1 (test double behavior - INFORMATIONAL)

**Performance Score**: 7/10

The branch improves overall system performance by preventing unbounded queries, but introduces a minor inefficiency with statement preparation inside methods.

---

## Merge Recommendation

**APPROVED WITH CONDITIONS**

The changes are performance-positive overall (pagination prevents memory exhaustion). The statement preparation issue should be fixed before merge as it's a simple change with clear benefit.

### Fix before merge:
1. Pre-compile the paginated `findAll` statements in constructors for both repositories

### Consider for follow-up PR:
1. Add pagination to `findByStatus()` for consistency
2. Document OFFSET pagination limitations in interface JSDoc

---

## Optimization Priority

**Fix before merge:**
1. Move `this.db.prepare()` calls from `findAll()` methods to constructors (HIGH)

**Optimize while you're here:**
1. Consider pagination for `findByStatus()` (MEDIUM)

**Future work:**
- Consider keyset pagination for very large datasets
- Add pagination to MCP tools that list tasks/dependencies

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*Generated by Performance Audit Specialist*
