I realize this question may not have an answer and therefore might not be suitable for SE, but I'm very curious about OP_RETURN transactions.

OP_RETURN transactions appear to be the accepted mechanism for inserting metadata into the Blockchain. Considering the innumerable uses for metadata (contracts, colored coins, proof of ownership...), I foresee more and more non-monetary transactions filling up the Blockchain.

Will that be bad?


It is reasonable solution. The main problem is not in the size of blockcain itself. The problem is in growing the number of unspent outputs. OP_RETURN outputs do not increase size of Utxo database

  • Why is "growing the number of unspent outputs" a "problem"? Aug 31 '14 at 16:26
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    @tim peterson: Client software needs to keep track of unspent outputs to be able to verify future transactions, so unspent transactions require storage space. It does not need to keep track of transactions that have already been spent; once it has used them to verify the following transactions, they could be discarded (though some clients like Bitcoin Core keep them around anyway). Aug 31 '14 at 19:03

I don't think so, because the use case of, "I need to pay (the equivalent of) five dollars to buy this comedian's work is more common than the use case of "I need to store this 128-bit string for an indefinite period of time."

Prediction: By the end of 2016, transactions intended to hold metadata instead of actually sending coins will make up less than 10% of the blockchain's size.

  • What will the % be in 2030? Right now in 2014 the % has to be way less than 1%, so anything even close to 10% would indicate a huge increase. Aug 31 '14 at 15:26

This is a subjective question of course, but you could view it simply as a technology finding its most compelling applications.

Eventually we will reach a time when transactions have to constantly complete for confirmation via the size of the miner fees that they attach.

When that happens, if people are willing to pay higher fees to embed metadata than to send bitcoins, then this will be the dominant use of the blockchain. If not, then not.

At Coin Secrets, we're currently seeing the OP_RETURN volume doubling every 10,000 blocks or so, i.e. every 70 days. We'll see if that continues.

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