AgentRules.org
RulesStacksClientsAuditorPrunerSelf-HealRFCsBenchmarkCLICI/CDAuthorsSubmit
This specification is maintained by the AgentRules Working Group. Have enhancements or want to claim maintainership?Submit Specification →
backendcritical PriorityID: postgres-17-wal-summarizer-consistency-guardrail

Postgres 17 WAL Summarizer Incremental Backup Consistency and LSN Monotonicity Guardrail

Mandates block-level WAL summary validation and strict LSN monotonicity enforcement across streaming replicas during PostgreSQL 17 incremental backups. Prevents broken restore chains and corrupted block delta states during pg_combinebackup operations caused by summarizer lag, missing summary spans, or timeline divergence.

Prohibited Anti-Pattern: Executing Incremental Backups Without WAL Summary Range Continuity and Replica Replay Monotonicity Validation

Export Ready-to-Drop Configuration

Select format below to copy code or download file directly.

---
description: Postgres 17 WAL Summarizer Incremental Backup Consistency and LSN Monotonicity Guardrail - Mandates block-level WAL summary validation and strict LSN monotonicity enforcement across streaming replicas during PostgreSQL 17 incremental backups. Prevents broken restore chains and corrupted block delta states during pg_combinebackup operations caused by summarizer lag, missing summary spans, or timeline divergence.
globs: src/**/*.ts, src/backup/**/*.ts, src/database/**/*.ts, infra/backup/**/*.ts
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/postgres-17-wal-summarizer-consistency-guardrail"
---

# Postgres 17 WAL Summarizer Incremental Backup Consistency and LSN Monotonicity Guardrail

> **Severity**: CRITICAL | **Category**: backend
> **Anti-Pattern Warning**: Executing Incremental Backups Without WAL Summary Range Continuity and Replica Replay Monotonicity Validation

## System Constraints
You are a Principal Database Reliability Engineer and Software Architect enforcing PostgreSQL 17 incremental backup invariants. You MUST mandate pre-flight verification of WAL summarization state, continuous LSN summary spans via pg_available_wal_summaries(), and strictly monotonic LSN checks across streaming standby nodes before incremental backup execution. Never permit incremental backup initiation against nodes where summarize_wal is disabled, where summary gaps exist between the prior backup manifest and current LSN, or where standby replay LSN lags behind the target incremental base.

## Strict Guidelines
- Services MUST ALWAYS verify that 'summarize_wal = on' and that the WAL summarizer background worker is actively running before initiating incremental backups.
- Engineers MUST ALWAYS query 'pg_available_wal_summaries()' to verify an unbroken, continuous LSN range from the previous backup manifest's 'End-LSN' to the target backup's start LSN.
- Services MUST NOT execute an incremental backup on a streaming standby replica unless the standby's replay LSN is strictly greater than or equal to the primary's latest summarized LSN.
- Engineers MUST ensure that differential recovery pipelines validate manifests with 'pg_verifybackup' prior to invoking 'pg_combinebackup'.
- Components NEVER trigger raw WAL removals or aggressive archive retention cleanup without asserting that WAL summary extraction has reached the target checkpoint horizon.

## Bad vs Good Implementations
### PostgreSQL 17 Incremental Backup Pre-Flight and Orchestration Guardrail

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: This implementation fails to verify that Postgres 17 WAL summarization is active and has no missing spans between the base backup LSN and current LSN. If summarize_wal is lagging or summaries are missing, the resulting backup will fail during pg_combinebackup, silently corrupting disaster recovery guarantees.
```typescript
import { Client } from 'pg';

interface BackupRequest {
  previousBackupManifestPath: string;
  isIncremental: boolean;
}

export async function runIncrementalBackup(client: Client, req: BackupRequest): Promise<void> {
  // FAILS: Directly triggering backup without verifying summarize_wal,
  // WAL summary file continuity, or standby replay monotonicity.
  if (req.isIncremental) {
    await client.query("SELECT pg_backup_start('incremental_backup', true)");
    // Backup transfer executed directly with unvalidated WAL summary state...
    await client.query("SELECT pg_backup_stop()");
  }
}
```

#### Production Standard (Correct)
> **Standard**: Validates that summarize_wal is enabled, verifies standby replay monotonicity relative to the parent backup's End-LSN, and queries pg_available_wal_summaries() to guarantee an unbroken chain of block delta summaries before executing backup routines.
```typescript
import { Client } from 'pg';

interface BackupManifestMeta {
  endLsn: string;
  timeline: number;
}

interface WalSummaryRange {
  timeline: number;
  start_lsn: string;
  end_lsn: string;
}

function parseLsn(lsn: string): bigint {
  const [hi, lo] = lsn.split('/').map((hex) => BigInt(`0x${hex}`));
  return (hi << 32n) | lo;
}

export async function assertWalSummarizerContinuity(
  client: Client,
  manifest: BackupManifestMeta,
  isStandby: boolean
): Promise<void> {
  const settingRes = await client.query<{ setting: string }>(
    "SELECT current_setting('summarize_wal') AS setting"
  );
  if (settingRes.rows[0]?.setting !== 'on') {
    throw new Error('Invariant Violation: Postgres 17 summarize_wal must be on.');
  }

  if (isStandby) {
    const replayRes = await client.query<{ replay_lsn: string }>(
      'SELECT pg_last_wal_replay_lsn() AS replay_lsn'
    );
    const currentReplay = parseLsn(replayRes.rows[0].replay_lsn);
    const requiredLsn = parseLsn(manifest.endLsn);
    if (currentReplay < requiredLsn) {
      throw new Error(`Standby replay LSN (${currentReplay}) lags behind base manifest LSN (${requiredLsn}).`);
    }
  }

  const summariesRes = await client.query<WalSummaryRange>(
    'SELECT tli AS timeline, start_lsn, end_lsn FROM pg_available_wal_summaries() ORDER BY start_lsn ASC'
  );

  const baseLsn = parseLsn(manifest.endLsn);
  const relevantSummaries = summariesRes.rows
    .filter((s) => s.timeline === manifest.timeline)
    .sort((a, b) => (parseLsn(a.start_lsn) < parseLsn(b.start_lsn) ? -1 : 1));

  let coveredLsn = baseLsn;
  for (const summary of relevantSummaries) {
    const start = parseLsn(summary.start_lsn);
    const end = parseLsn(summary.end_lsn);
    if (start <= coveredLsn && end > coveredLsn) {
      coveredLsn = end;
    }
  }

  if (coveredLsn <= baseLsn) {
    throw new Error(`No WAL summary range covers base LSN: ${manifest.endLsn}`);
  }
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

PostgreSQL Diagnostic MCP Server
Exposes low-level PostgreSQL runtime stats, WAL summary inspection queries, and replication lag state to AI agents.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

pg_combinebackup Verification CLI Skill
Validates synthesized Postgres 17 full backups from incremental chains and checks manifest integrity via pg_verifybackup.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Postgres 17 WAL Summarizer Incremental Backup Consistency and LSN Monotonicity Guardrail

Postgres 17 WAL Summarizer Incremental Backup Consistency and LSN Monotonicity Guardrail defines an industrial-grade behavioral standard for backend engineering. Mandates block-level WAL summary validation and strict LSN monotonicity enforcement across streaming replicas during PostgreSQL 17 incremental backups. Prevents broken restore chains and corrupted block delta states during pg_combinebackup operations caused by summarizer lag, missing summary spans, or timeline divergence. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Executing Incremental Backups Without WAL Summary Range Continuity and Replica Replay Monotonicity Validation Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftExecuting Incremental Backups Without WAL Summary Range Continuity and Replica Replay Monotonicity ValidationCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Services MUST ALWAYS verify that 'summarize_wal = on' and that the WAL summarizer background worker is actively running before initiating incremental backups.

Services MUST ALWAYS verify that 'summarize_wal = on' and that the WAL summarizer background worker is actively running before initiating incremental backups.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST ALWAYS query 'pg_available_wal_summaries()' to verify an unbroken, continuous LSN range from the previous backup manifest's 'End-LSN' to the target backup's start LSN.

Engineers MUST ALWAYS query 'pg_available_wal_summaries()' to verify an unbroken, continuous LSN range from the previous backup manifest's 'End-LSN' to the target backup's start LSN.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Services MUST NOT execute an incremental backup on a streaming standby replica unless the standby's replay LSN is strictly greater than or equal to the primary's latest summarized LSN.

Services MUST NOT execute an incremental backup on a streaming standby replica unless the standby's replay LSN is strictly greater than or equal to the primary's latest summarized LSN.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Engineers MUST ensure that differential recovery pipelines validate manifests with 'pg_verifybackup' prior to invoking 'pg_combinebackup'.

Engineers MUST ensure that differential recovery pipelines validate manifests with 'pg_verifybackup' prior to invoking 'pg_combinebackup'.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Components NEVER trigger raw WAL removals or aggressive archive retention cleanup without asserting that WAL summary extraction has reached the target checkpoint horizon.

Components NEVER trigger raw WAL removals or aggressive archive retention cleanup without asserting that WAL summary extraction has reached the target checkpoint horizon.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Postgres 17 WAL Summarizer Incremental Backup Consistency and LSN Monotonicity Guardrail critical for AI coding assistants?

Mandates block-level WAL summary validation and strict LSN monotonicity enforcement across streaming replicas during PostgreSQL 17 incremental backups. Prevents broken restore chains and corrupted block delta states during pg_combinebackup operations caused by summarizer lag, missing summary spans, or timeline divergence. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Executing Incremental Backups Without WAL Summary Range Continuity and Replica Replay Monotonicity Validation) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

Citation & Open Source Attribution Guidelines

This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

Related BACKEND Rules

View all rules →
backend
42

Fastify 5 Schema Compilers & Encapsulation Production Standard

Fastify relies on lexical encapsulation contexts to sandbox decorators, hooks, and compiled validation/serialization schemas without memory leaks or cross-tenant bleed. In Fastify 5, misuse of global compilers or failing to encapsulate plugin boundaries causes compiled `fast-json-stringify` serializers and Ajv validators to either crash on duplicate IDs, leak private data across sibling scopes, or bypass JIT compilation optimizations. Production services must enforce strict encapsulation hierarchies and type-safe schema compilation across every routing subtree.

backend
68

Bun Embedded SQLite WAL Mode & Transaction Synchronization Standard

Production database standard for bun:sqlite. Mandates enabling Write-Ahead Logging (PRAGMA journal_mode = WAL), busy timeouts, and using db.transaction() for atomic operations without lock starvation.

backend
68

Drizzle ORM Batch API & Interactive Transaction Isolation Standard

Production database standard for Drizzle ORM (PostgreSQL & MySQL). Mandates using db.batch() over HTTP drivers to prevent round-trip waterfalls, explicit db.transaction() with serializable/read-committed isolation, and strictly avoids unawaited query promises.

1 Rule in Stack

Postgres