Yes, but that has no impact on the cost. It's a flat rate in 64kb blocks. Batching and compression would only affect the networking fees from Google, not the per API call fees. If you batch up 64 1kb messages into a single batch then Google still bills you for 64 publish API calls.
If you look at the API, the publish API allows you to push multiple messages in a single API call, and if that is the batching - publishing multiple messages - then yes, you and others are absolutely correct that there is no cost benefit.
But rather than publishing
{
"messages" : [
{ message 1 }, { message 2 }
]
}
You publish
{
"messages" : [
{ container message containing both, still less than 64k }
]
}
Then you've reduced your operations count by half. Cloud services like this have a per message overhead, for things like auditing and delivery tracking, which is why the pricing model is what it is.
If you are ok with having to unpack and process multiple messages at once as I've described, then it's a way to optimize against the pricing model.
The Spotify graphs from Google's monitoring support the numbers I quoted. They may well be batching but Google is seeing (and billing) the numbers I quoted.
If 2M requests result in 1 Gb network traffic, each message is 500 bits (~60 bytes). Theoretically, that's 1K messages per batch.
Even if practically that number is much lower (around 100 per batch), the cost ends up becoming around $3,000 for the messages and $9,000 for the network, so roughly $12,000 per month.
