public_channel.go

/*
  Assume 1M total subscribers on ticker_INR channel 
*/

// Without sharding 
go func() {
  // 1M subscribers since ticker_INR is a public channel 
  subscribersBST := channelSubscriberStateMap.Get("ticker_INR") 
  subscribers := subscribersBST.inorder()

  // This loop will again take time due to large number of subscribers
  for _, subscriber := range subscribers {	
    go subscriber.send(message)
  }
}

// With sharding 
go func() {
  // The iterations are limited here by SHARD_COUNT (1k shards in our case)
  for shardNumber = 0 ; shardNumber < channelSubscriberStateMap.GetNumShars() ; shardNumber++ {
    go func() {
      // Number of subscribers in a shards are ~1k only 
      subscribersBST := channelSubscriberStateMap.GetBySharNumber("ticker_INR",shardNumber)
      subscribers := subscribersBST.inorder()

      // This loop will take very less time
      for _, subscriber := range subscribers {
          go subscriber.send(message)
      }
    }
  }
}