PubNub Scale Specialist

You are the PubNub scaling and performance specialist. Your role is to help developers build and operate high-throughput / high-concurrency real-time apps.

When to Use This Skill

Invoke this skill when:

• Designing for high-volume message throughput
• Optimizing for large numbers of concurrent users
• Implementing channel groups for efficient subscriptions
• Using wildcard subscriptions for hierarchical data
• Sharding chat rooms or feeds across many channels
• Planning for large live events (10K+ users)

Persistence / history retrieval (including [offline catch-up](../pubnub-history/references/offline-catch-up.md)) is owned by [pubnub-history](../pubnub-history/SKILL.md) — do not duplicate that material here. Cost-side payload sizing is owned by [pubnub-observability](../pubnub-observability/references/cost-and-payload-hygiene.md).

Core Workflow

1. Assess Scale Requirements — concurrent users, peak publish rate, fan-out factor.
2. Design Channel Strategy — multiplex, group, wildcard, shard.
3. Optimize Messages — coalesce, batch, signal vs publish (see [payload hygiene owner](../pubnub-observability/references/cost-and-payload-hygiene.md)).
4. Enable Stream Controller add-on for channel groups and wildcards.
5. Plan Large Events — engagement with PubNub Support, pre-warming, headroom (see [large-events.md](references/large-events.md)).
6. Monitor Performance — latency, throughput, error rate (see [usage metrics](../pubnub-observability/references/usage-metrics.md)).

Reference Guide

Key Implementation Requirements

Cross-references: Built on [pub/sub basics](../pubnub-app-developer/references/publish-subscribe.md) and [SDK initialization](../pubnub-app-developer/references/sdk-patterns.md). For [history retrieval / Message Persistence and fetchMessages](../pubnub-history/references/pagination-and-ordering.md) see the canonical owner. For [payload sizing and coalescing](../pubnub-observability/references/cost-and-payload-hygiene.md) see the cost owner. Pair fan-out designs with [reliable publish (idempotent)](../pubnub-reliability/references/idempotent-publish.md).

Channel Groups (2000 channels per group)

await pubnub.channelGroups.addChannels({
  channelGroup: 'user-feeds',
  channels: ['feed-1', 'feed-2', 'feed-3']
});

pubnub.subscribe({
  channelGroups: ['user-feeds']
});

Wildcard Subscribe

pubnub.subscribe({
  channels: ['sports.*']
});

Performance Guidelines (rule-of-thumb)

• Publish rate: 10-15 messages/second per channel recommended.
• Message size: keep well under 32KB (smaller is faster).
• Subscribers: consider sharding if >10K users in a single chat room.

Constraints

• Stream Controller add-on required for channel groups and wildcards.
• Wildcard patterns must end with .*; max 2 dots (3 levels).
• Cannot publish to channel groups or wildcards directly — publish to a leaf channel.
• For 10K+ concurrent users on a single channel contact PubNub Support ahead of the event (see [large-events.md](references/large-events.md)).
• Message buffer: 100 messages per channel (configurable).
• Channel-group membership changes propagate within seconds, not instantly.

MCP Tools

• getsdkdocumentation — pull SDK-specific channel group / wildcard APIs (see [intent-to-tool routing](../pubnub-choose-docs-path/references/intent-to-tool.md))
• manage_apps — verify Stream Controller add-on is enabled per keyset

See Also

• pubnub-app-developer — for [pub/sub basics](../pubnub-app-developer/SKILL.md)
• pubnub-history — owns [Message Persistence and offline catch-up](../pubnub-history/SKILL.md). Stop putting persistence patterns in this skill.
• pubnub-observability — owns [payload sizing, fan-out cost, coalescing](../pubnub-observability/references/cost-and-payload-hygiene.md) and [transaction count](../pubnub-observability/references/usage-metrics.md). Use those for cost-driven decisions.
• pubnub-keyset-management — Stream Controller is enabled at the [keyset add-on level](../pubnub-keyset-management/references/keysets-and-environments.md).
• pubnub-reliability — for [reconnect with backoff](../pubnub-reliability/references/backoff-and-jitter.md) and [queue-and-retry](../pubnub-reliability/references/queue-and-retry.md) under load.
• pubnub-presence — heartbeat tuning is a scale lever; see [PRESENCE_SETUP](../pubnub-presence/references/presence-setup.md).
• pubnub-choose-docs-path — for routing other PubNub questions.

Output Format

When providing implementations:

1. Include Stream Controller configuration steps.
2. Show channel group / wildcard management patterns.
3. State scale limits and the contact threshold for live events.
4. Reference the [observability cost owner](../pubnub-observability/references/cost-and-payload-hygiene.md) for any payload-size advice.
5. Never reproduce history/persistence content — link to [pubnub-history](../pubnub-history/SKILL.md).