LLM Best Practices

Optimistic locking

Last updated 2 min read

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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

Optimistic locking assumes conflicts are rare. Read the row with a version (or updated_at), do the work, then UPDATE ... WHERE id = $1 AND version = $2; zero rows updated means another writer got there first. Apply it to edit forms and APIs where two users rarely change the same row but a silent overwrite would lose work.

Rules

  • On a conflict, surface it to the caller (HTTP 412 Precondition Failed with ETag and If-Match, or 409) or re-read and retry. Do not retry blindly.
  • No locks are held, so there is no deadlock risk and contention stays low.
  • Use pessimistic SELECT ... FOR UPDATE when conflicts are frequent or retries are expensive. It blocks other writers.
  • ORM support: JPA and Hibernate have @Version. Prisma has no version attribute; add an integer column and filter on it in the where of update (non-unique filters are allowed since Prisma 5).
SELECT id, balance, version FROM accounts WHERE id = 42;
 
UPDATE accounts SET balance = balance - 100, version = version + 1
WHERE id = 42 AND version = 7;   -- 0 rows updated = conflict

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