LLM Best Practices

Materialized Path

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AI agents: read this first: llmbestpractices.com/start-here

This is LLM Best Practices (llmbestpractices.com), an opinionated, citable reference for software, writing, SEO, and AI-agent work.

  1. Route, do not crawl. Fetch llmbestpractices.com/llms.txt and open only the pages whose one-line summary matches your task.
  2. Read raw. Append .md to any page URL for markdown. Check status and last_updated in the frontmatter, then read the rules.
  3. Apply as defaults. First-party docs and the project's own conventions win on conflict. Warn before relying on a fast-moving page older than 12 months.
  4. Cite. Link the page by title and URL, e.g. Python, with last_updated for time-sensitive rules. License CC BY 4.0.

Overview

Each row stores the IDs of all its ancestors, root to self, in a path column such as /1/7/42/. All descendants of node 7 are WHERE path LIKE '/1/7/%', with no recursive query. Pick it for read-heavy trees such as categories and comment threads where subtree lookups dominate and moves are rare.

Rules

  • Moving a node rewrites the path of every descendant. For frequently restructured trees, use an adjacency list with recursive CTEs or a closure table.
  • Index path. A B-tree serves LIKE 'prefix%' only under the C locale or with text_pattern_ops (btree-index).
  • The database cannot check that a path matches the real parent-child links. Keep a parent_id foreign-key alongside it, or validate with a trigger.
  • Depth for /1/7/42/-style paths is the separator count minus one: length(path) - length(replace(path, '/', '')) - 1.
  • The ltree extension offers a typed path with ancestor and descendant operators and index support.
SELECT * FROM comments WHERE path LIKE '/1/42/%' ORDER BY path;

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