Convex Performance Patterns

Overview

Convex is designed for performance, but requires specific patterns to achieve optimal results. This skill covers denormalization strategies, index design, avoiding common performance pitfalls, and handling concurrency with OCC (Optimistic Concurrency Control).

TypeScript: NEVER Use any Type

CRITICAL RULE: This codebase has @typescript-eslint/no-explicit-any enabled. Using any will cause build failures.

When to Use This Skill

Use this skill when:

• Queries are running slowly or causing too many re-renders
• Designing indexes for efficient data access
• Avoiding N+1 query patterns
• Handling high-contention writes (OCC errors)
• Denormalizing data to improve read performance
• Optimizing reactive queries
• Working with counters or aggregations

Core Performance Principles

Principle 1: Queries Should Be O(log n), Not O(n)

Convex queries should use indexes for efficient data retrieval. If you're scanning entire tables, you're doing it wrong.

Principle 2: Denormalize Aggressively

Convex has no joins. Embed related data or maintain lookup tables.

Principle 3: Minimize Document Reads

Each document read in a query creates a dependency. Fewer reads = fewer re-renders.

Principle 4: Avoid Hot Spots

Single documents that are frequently written will cause OCC conflicts.

Denormalization Patterns

Pattern 1: Embed Related Data

❌ BAD: N+1 queries

export const getTeamWithMembers = query({
  args: { teamId: v.id("teams") },
  returns: v.null(),
  handler: async (ctx, args) => {
    const team = await ctx.db.get(args.teamId);
    if (!team) return null;

    // ❌ This triggers N additional reads, each causing re-renders
    const members = await Promise.all(
      team.memberIds.map((id) => ctx.db.get(id))
    );
    return { team, members };
  },
});

✅ GOOD: Denormalize member info into team

// Schema: teams.members: v.array(v.object({ userId: v.id("users"), name: v.string(), avatar: v.string() }))
export const getTeamWithMembers = query({
  args: { teamId: v.id("teams") },
  returns: v.union(
    v.object({
      _id: v.id("teams"),
      _creationTime: v.number(),
      name: v.string(),
      members: v.array(
        v.object({
          userId: v.id("users"),
          name: v.string(),
          avatar: v.string(),
        })
      ),
    }),
    v.null()
  ),
  handler: async (ctx, args) => {
    return await ctx.db.get(args.teamId); // Single read, includes members
  },
});

Pattern 2: Denormalized Counts

Never .collect() just to count.

❌ BAD: Unbounded read

const messages = await ctx.db
  .query("messages")
  .withIndex("by_channel", (q) => q.eq("channelId", channelId))
  .collect();
const count = messages.length;

✅ GOOD: Show "99+" pattern

const messages = await ctx.db
  .query("messages")
  .withIndex("by_channel", (q) => q.eq("channelId", channelId))
  .take(100);
const count = messages.length === 100 ? "99+" : String(messages.length);

✅ BEST: Denormalized counter table

// Maintain a separate "channelStats" table with messageCount field
// Update it in the same mutation that inserts messages

export const getMessageCount = query({
  args: { channelId: v.id("channels") },
  returns: v.number(),
  handler: async (ctx, args) => {
    const stats = await ctx.db
      .query("channelStats")
      .withIndex("by_channel", (q) => q.eq("channelId", args.channelId))
      .unique();
    return stats?.messageCount ?? 0;
  },
});

export const addMessage = mutation({
  args: { channelId: v.id("channels"), content: v.string() },
  returns: v.id("messages"),
  handler: async (ctx, args) => {
    const messageId = await ctx.db.insert("messages", {
      channelId: args.channelId,
      content: args.content,
    });

    // Update denormalized count
    const stats = await ctx.db
      .query("channelStats")
      .withIndex("by_channel", (q) => q.eq("channelId", args.channelId))
      .unique();

    if (stats) {
      await ctx.db.patch(stats._id, { messageCount: stats.messageCount + 1 });
    } else {
      await ctx.db.insert("channelStats", {
        channelId: args.channelId,
        messageCount: 1,
      });
    }

    return messageId;
  },
});

Pattern 3: Denormalized Boolean Fields

When you need to filter by computed conditions, denormalize the result:

// Schema
export default defineSchema({
  posts: defineTable({
    body: v.string(),
    tags: v.array(v.string()),
    // Denormalized: computed on write
    isImportant: v.boolean(),
  }).index("by_important", ["isImportant"]),
});

// Mutation: compute on write
export const createPost = mutation({
  args: { body: v.string(), tags: v.array(v.string()) },
  returns: v.id("posts"),
  handler: async (ctx, args) => {
    return await ctx.db.insert("posts", {
      body: args.body,
      tags: args.tags,
      isImportant: args.

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