mattermost/server/channels/README.md

Server Channels Review Guidelines

When reviewing or writing code in the server channels package, focus on SQL query performance and API layer efficiency.

SQL Store Layer

• Run EXPLAIN ANALYZE on new or modified queries against a large dataset before merging. A query that performs well on a 12M-post database may degrade significantly at 100M+ posts.
• Watch for sequential scans on large tables. Ensure appropriate indexes exist for new query patterns.
• When adding new queries to the store, check whether an existing query already fetches the needed data. Avoid duplicate round trips to the database.

API Layer

• Minimize database round trips. If an endpoint calls a Get followed by a Delete on the same row, consider using DELETE ... RETURNING to combine them into a single query.
• Don't add queries that are unnecessary for the operation. The most efficient work is the work you don't do.
• When adding new API endpoints, add them to the load test tooling so performance can be validated under realistic concurrency.

Permissions and Security

• Verify that new endpoints enforce appropriate permissions. Rely on the dedicated security review for thorough coverage, but flag anything obviously missing (e.g., an endpoint that skips permission checks entirely).