Quote from: genjix on June 03, 2013, 06:04:41 PM

I personally believe that disk space is not a big deal (current unmodified chain is 15 Gb). I'm more worried about fetch speed (not writes) and scalability.

I'm thinking about building a device for secure Bitcoin storage based on the Raspberry Pi. It doesn't have to be very fast, but if I want to support a full blockchain for a number of years into the future, the storage would get prohibitive (already is). That's why I'm interested in a pruned blockchain.

I'd much rather use (and possibly contribute to) an existing library than writing my own stuff.

Quote from: genjix on June 03, 2013, 06:04:41 PM

SQL is too slow for blockchains.

Could you elaborate on that? What are the operations that require high speed of database access? I am considering using sqlite for a pruned blockchain, do you think that would not work?

Could I write my own implementation of blockchain which automatically pruned itself without rebuilding, and stored the database (blockchain, transactions, addresses maybe) in its own database? Would it create problems for the rest of libbitcoin?

Quote from: genjix link=topic=30646.msg2360452#msg2360452

Yeah you can do that if you rebuild the database.
That means creating a new database (see examples/initchain.cpp), then importing the old blocks into the new one.

Sounds expensive.

I wish there were a bit more comments in the code to explain the concepts, like slices, what the chain keeper, chain organizer do, etc.

Quote from: genjix link=topic=30646.msg2360452#msg2360452

There is a method to delete from the blockchain directly, but I haven't exposed that. It's used for blockchain reorgs. You can use that same code, but make sure you stop the blockchain object before modifying the database. You can then reopen it after:

Code:

leveldb_blockchain* chain = new leveldb_blockchain(pool);
chain->start(dbpath, blockchain_started);
// ... do stuff
// stop/join threadpools using the blockchain.
chain->stop();
delete chain;
// open database, delete whatever you want.
leveldb_blockchain* chain = new leveldb_blockchain(pool);
chain->start(dbpath, blockchain_started);
// continue from where you left off...

something like that.

see the method called "end_slice"

https://github.com/spesmilo/libbitcoin/blob/master/src/blockchain/leveldb/leveldb_chain_keeper.cpp

It's deleting a bunch of blocks from the end of the blockchain.

Thanks for the pointers.

Why does the database need to be deleted and then opened in order to delete data from it?

Quote from: genjix link=topic=30646.msg2360452#msg2360452

Also `bool leveldb_chain_keeper::clear_transaction_data(leveldb_transaction_batch& batch, const transaction_type& remove_tx)' (same file) might interest you too. It's deleting specific transactions from the database.

Where can I find a description of what's in the database? I'm used to SQL databases with tables, but I understand leveldb only stores key-value pairs? What objects are in the database? Is there for instance a way to find unspent transactions?