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Subscription Monitoring

Monitor your Meteor DDP subscriptions with detailed performance metrics.

What Gets Tracked​

For each subscription, SkySignal captures:

FieldDescription
subscriptionNameThe name of the publication
responseTimeTime to initial data delivery
documentsAddedNumber of documents sent
documentsChangedDocuments updated during subscription
documentsRemovedDocuments removed during subscription
dataTransferredApproximate bytes transferred
userIdThe subscribing user
timestampWhen the subscription started

Viewing Subscription Data​

Subscriptions Dashboard​

Navigate to your site's Subscriptions tab to see:

  • Active Subscriptions - Currently active subscription count
  • Response Time Trends - Historical performance data
  • Top Subscriptions - Most frequently used publications
  • Data Transfer - Bandwidth usage by subscription

Subscription Details​

Click on any subscription to view:

  • Average response time and percentiles
  • Document count statistics
  • Data transfer metrics
  • Sample subscription instances

Configuration​

Enable/Disable Subscription Tracking​

SkySignal.init({
  apiKey: '...',
  trackSubscriptions: true,  // Enable (default)
});

Ignore Specific Subscriptions​

Exclude subscriptions from tracking:

SkySignal.init({
  apiKey: '...',
  ignoreSubscriptions: [
    'meteor.loginServiceConfiguration',  // Built-in Meteor sub
    /^internal\./,                        // Internal subscriptions
  ],
});

Understanding Metrics​

Response Time​

The time from subscription request to onReady() callback:

// In your client code
Meteor.subscribe('posts', function onReady() {
  // SkySignal measures time until this callback fires
});

Document Metrics​

  • Added - Initial documents sent when subscription starts
  • Changed - Updates pushed to the client
  • Removed - Documents removed from the subscription

Data Transfer​

Estimated bytes transferred, calculated from:

  • EJSON-serialized document size
  • Number of documents sent

Performance Insights​

Identifying Large Subscriptions​

Watch for subscriptions with:

  • High documentsAdded counts (sending too much data initially)
  • Large dataTransferred values
  • Long response times

Common Issues​

Subscription sends too many documents​

// Bad: Publishes all posts
Meteor.publish('posts', function() {
  return Posts.find();  // Could be thousands of documents!
});

// Good: Limit and paginate
Meteor.publish('posts', function(limit = 20) {
  check(limit, Number);
  return Posts.find({}, {
    limit: Math.min(limit, 100),
    sort: { createdAt: -1 }
  });
});

Subscription is slow to become ready​

Common causes:

  • Large initial dataset
  • Missing database indexes
  • Complex publication logic

Best Practices​

1. Paginate Large Collections​

Never send all documents at once:

Meteor.publish('posts.paginated', function(page = 1, limit = 20) {
  check(page, Number);
  check(limit, Number);

  const skip = (page - 1) * limit;
  return Posts.find({}, {
    skip,
    limit: Math.min(limit, 100),
    sort: { createdAt: -1 }
  });
});

2. Use Field Filtering​

Only publish needed fields:

Meteor.publish('users.list', function() {
  return Meteor.users.find({}, {
    fields: {
      username: 1,
      'profile.avatar': 1,
      // Don't send emails, settings, etc.
    }
  });
});

3. Index Your Queries​

Ensure MongoDB indexes exist for your publication queries:

// In your collection file
Posts.createIndex({ createdAt: -1 });
Posts.createIndex({ authorId: 1, createdAt: -1 });

4. Consider Publication Merging​

For complex UIs, consider using reywood:publish-composite:

Meteor.publishComposite('postWithAuthor', function(postId) {
  return {
    find() {
      return Posts.find({ _id: postId });
    },
    children: [{
      find(post) {
        return Meteor.users.find({ _id: post.authorId }, {
          fields: { username: 1, 'profile.avatar': 1 }
        });
      }
    }]
  };
});

Troubleshooting​

Subscriptions Not Tracked​

  1. Verify trackSubscriptions: true
  2. Check if subscription is in ignoreSubscriptions
  3. Ensure agent initializes before publications are defined

Inaccurate Document Counts​

Document counts may not match exactly if:

  • Documents are added/removed during the subscription lifecycle
  • Multiple publications affect the same collection

Next Steps​