I was making my daily rounds checking various stats sites about the bitcoin ecosystem. I periodically check bitcoin mempool fullness, prices of btc, bch, etc, and a few other things as I am sure many on this forum do. I happened to notice that bitcoin cash just mined a very large block, 3.5 mb to be exact, and that r/btc had a post about it. So I went and had a look and much to my surprise, this massive block only has 509 transactions in it (a typical block has about 2000 transactions per mb).
For those interested here is the block on a block explorer showing the individual transactions in the block (warning, very large page load):
So I decide to start poking around a bit and see what kind of transactions are in this block. I expected to find a single massive transaction and a few other “normal ones”. The normal ones were there as expected, but instead of one big transaction there are dozens of transactions of all nearly identical format. Each of these transactions consists of a few hundred inputs, being aggregated to a single (or a few in some cases) output.
Ok, so this looks like a spam transaction, but most spam transactions are someone taking a single input and fanning out to hundreds of outputs to bloat the mempool/blockchain. This one seems to be doing the opposite, taking hundreds of inputs and sweeping them to single outputs. Still could be a spammer, just cleaning up their spammy mess, rather than creating it. To find out, let’s go one step back and look at the individual inputs to the transactions and when they were spent last (click “prev tx” by one of the inputs to see the transaction that created that particular UTXO). Although I don’t have software to aggregate them properly and see when all of them were created, even a cursory glance clicking through them shows that the overwhelming majority were created in during periods when the mempool was experiencing very heavy loads.
Now it is important to state that we don’t know why this person is doing these transactions. This could be an exchange sweeping up deposits for cold storage, or a tumbler, or some other thing; but it also could be someone making transactions purely to bloat the mempool. Also, it is important to note that even though this particular block is on the Bitcoin Cash side of the fork, the UTXO inputs that it is sweeping up are from before the fork happened. So the transactions that created all these UTXOs happened on the main (and at the time only) bitcoin chain.
Anyway, this is my initial, very rough, analysis of this very large block. At this point I am inclined to say it is likely a spammer sweeping up their spam transactions, but more analysis has to be done before we can say that with certainty. I hope others with more technical knowledge can have a deeper and more analytical look at this data. I was just clicking through the UTXOs in my broswer and making a mental note of the dates, so this is hardly scientfic, however it is impossible not to notice that these dates are not random, but are all clustered around specific points in time. I would really like to see someone download this block and parse all the inputs to see when they date from and aggregate this into a graph.