MultiChain as distributed MVCC

Question

Basically, I want to put an arbitrary database on a blockchain (let's assume for argument's sake that I'm not trying to squeeze a silly amount of data into every transaction).

In this blog post, http://www.multichain.com/blog/2015/07/bitcoin-vs-blockchain-debate/, Gideon refers to using a blockchain as a form of distributed multiversion concurrency control for a database.

How would I go about using MultiChain to do this? My initial attempts have been to change a row of a table into a stringified JSON object, to be sent as transactional metadata. This feels hackish though. Is there a better way?

Answer 1

Interesting question. You would actually need to express each row of the database table as metadata within a single transaction output, rather than per-transaction, i.e. using OP_DROP within that output script. MultiChain doesn't currently provide an easy API for doing this, so you'd need to create a raw transaction using createrawtransaction, then find a library which picks apart and puts together bitcoin transactions, and add the OP_DROP inside the script for the output. You can find some code for doing decoding and encoding transactions in our OP_RETURN libraries for PHP and Python: https://github.com/coinspark

Comments

Thanks for the response, and thanks for the resources. I'll be sure to have a look at them.

I don't understand fully what you mean by "express each row of the database table as metadata within a single transaction output, rather than per-transaction".

Do you mean that whenever there's a change to the database table, I would keep things up to date by
 * encoding the entire database table as metadata
 * making a transaction containing this metadata

so that the entire network sees this on the blockchain, and hence can see what the database should look like?

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Every database transaction deletes some rows and inserts others. (Modifying a row is equivalent to delete the old version of that row and creating a new one in its place.) Each deleted row is one input of a blockchain transaction, and each created row is one output, with the content of the rows encoded as OP_DROP metadata within that output.