I think it's very important to be able to browse through all the records in a shortest possible time.

for utxo, my approach with iguana creates a parallel set of datasets in read only memory mapped files. Arguably, this is the ultimate DB as it simply cant get any faster than this.

All things needed for block explorer level queries are precalculated and put into the read only files.

By having each bundle of 2000 blocks being mostly independent of all other blocks, this not only allows for parallel syncing of the blockchain but also using multiple cores for all queries regarading tx history.

I also calculate all address balances for each bundle, so by adding all the values across all the bundles you end up with the current balance as of the most recent bundle. Special case handling of the realtime bundle gets us up to date block explorer data for all blocks, tx, addresses (even multisig)

I dont quite have everything done, but the basic structure is showing very good results. I also remove as much redundancy as possible during the creation of the read-only files so instead of taking more space than the raw blockchain, it ends up taking about half the space. About half of that is the signatures, which can be purged for non-relaying nodes after it has been validated.

The format of the utxo vector would just be the location of the unspent that is being spent and the location of the spend is implicit in the order of the vins.

[u0, u1, u2, u3, ...] is a list of 6 byte locators for the unspent that the corresponding vin in the bundle is spending, where each ui contains the bundle id and the unspentind. Each unspentind is simply the order it appears in the bundle (starting at 1).

the above is not directly usable, but it is invariant and can be created once and put into the read-only file(system). using mksquashfs reduces the size of the index tables by almost 50%.

Given such a list for all bundles, then using a parallel multicore process, they can all be traversed and update a bitmap to indicate which outputs are spent. So a 0 bit for this means it is unspent. Maybe 1 bit of space per utxo is good enough, as that is seemingly as good as it gets, but it is 1 bit per vout, so more like 30MB size. However, I think this can be compressed pretty good with most of the early vouts already being spent (ignoring the satoshi ones). I havent had a chance to get an up to date utxo bitmap, but I hope to get one in the next week.

At the 30MB size or smaller, the entire utxo bitmap will fit into CPU L cache and provide 10x faster performance than RAM. RAM is actually quite slow compared to things that can be done totally inside the CPU.

James

In its raw form with all the data scattered across the 200 bundles, a simplistic search for a specific address took 2.5 milliseconds on a 1.4Ghz i5. Not a parallel process, but serial. Using faster CPU and 8 cores, I think times of 100 nanoseconds could do a complete search and sum for a specific address.

Not sure what sort of things "like to do anything on each single one of them" you would want to do across all UTXO. To my thinking, other that total balance, the UTXO is not spanning across all addresses, so if you can extract all the relevant tx per address efficiently, that is sufficient.

Once all the balances for all the addresses are verified at all the bundle boundaries, then "all" that is left is the realtime bundle being validated. The brute force way would just be to generate a bundle without all the blocks, as each new block come in. I guess it wont be so bad as both the bloom filter and the open hashtable was designed to be able to be incrementally added to.

I think it's very important to be able to browse through all the records in a shortest possible time.

You're mixing up things. Probably because you don't really understand what the UTXO database actually does inside the bitcoin software.

Spreed of accessing the records is important for obvious reasons.
The traditional reason is that you want to verify new transactions/blocks quickly and efficiently.
And the new reasons, like hardware wallets or any kind of stealth payments.

The current approach from the satoshi's client, where the wallet is glued to the node and keeps track of its addresses, updating their balance as new blocks appear - IMHO this solution has proven to be unreliable. Plus is totally unfeasible for private offline wallets.

An efficient UTXO database that can quickly browse through all the records is definitely a must for the next generation of bitcoin node software.
I am just not aware of any existing engines that would be ready to replace the currently used leveldb.
I think one eventually needs to be (and will be) created explicitly for Bitcoin. Just like sipa's secp256k1 lib was created explicitly for Bitcoin, as the originally used openssl's implementation wasn't good enough to handle a crucial part of the software.

A Miner Problem

Posted on March 2, 2016  by  Mircea Popescu   
  
As announced in #bitcoin-assets, BitBet was attacked earlier today through a transaction withholding mechanism. The attack unfolded as follows :

1. A BitBet bet (Jeb Bush will be Republicans' 2016 Presidential Nominee) was closed and resolved on 21 February. This created a list of winners with a reasonable expectation to be paid their winnings.

2. A first transaction was broadcast, to satisfy the claims of the winners, spending some inputs, and offering a fee of 0. This transaction was, as you'd expect, neither mined nor included in the mempools of most Bitcoin nodes.

3. A second transaction was broadcast, spending the same inputs as A1, including a fee of 0.0001, call it A2. For a ~1.5kb transaction, this fee is on the low side, so it perhaps could be argued that it not being mined would be expected. Nevertheless, transaction A2 was also not included in the mempools of most Bitcoin nodes.

4. As neither transaction A1 or A2 were mined after 54 (48) hours, a further transaction was broadcast, spending the same inputs as A1 and A2, and including a fee of 0.000175, call it A3. By any measure, a fee in excess of 10 satoshi per byte should be sufficient to have transactions mined. Nevertheless, contrary to expectation, transaction A3 was not included in either a block or the mempools of most Bitcoin nodes.

5. After a further 48 hours, a fourth transaction was broadcast, spending the same inputs as A1, A2 and A3, and including a fee of 0.00022, call it A4. Just like the previous three, transaction A4 was not either included in a block or advertised by most Bitcoin nodes.

6. After a further 16 hours, transaction B was broadcast, that included the same outputs as transactions A1-A4, but different inputs. Transaction B, like transaction A4, included a fee of 0.00022. Transaction B was advertised by most Bitcoin nodes immediately thereafter, and was included in a block within half hour of being broadcast.

7. Two hours after B was included in a block, transaction A1 was re-broadcast by an unknown third party. Twenty minutes later, the 0 fee, week old, not-advertised-by-anyone-ever transaction was included in a block.

On the basis of these events, the following allegations can readily be supported :

• That the notion of "a majority of Bitcoin nodes" is void of content, most of the relay network being under the control of the same entity and supporting functionality not contemplated by the Bitcoin protocol (such as selective mothballing of specific transactions).(1) This specifically means that "someone"(2) has the ability to nuke transactions out of the network irrespective of whether they are validly signed or not, directly replicating functionality already available to fiat governments in fiat payment processors such as Visa or Paypal.

• That a cartel of Bitcoin miners is deliberately and systematically withholding blocks for an interval of about 20 minutes to a half hour, so as to ensure themselves a (significant) advantage over any would-be competitors.(3)

• That neither above item makes sense or could long survive without the other, meaning that necessarily the culprit is one and the same. Note for the record that an entity controlling 51% of the network (as is by a large margin the case with the Antpool/F2pool cartel) can safely withhold blocks for an indefinite period – if a competitor publishes a longer chain all the cartel has to do is keep mining on its own, eventually they'll prevail.(4)

Note that there are no alternative theories that more parsimoniously explain the chain of observed phenomena, and consequently the validity of the above allegations is a matter of objective truth. One may disagree on the strength of subjective feeling, or put forth his own interpretations, but these – much as in the case of alternative explanations for biological evolution – suffer from a fundamental logical weakness.

Update March 2, 2016 18:49 UTC:  In a further development on this story, Bitbet has now announced a moratorium on payments until the issue is resolved. (N. ed.)

1. You should remember that the Bitcoin relay network has for many years been in very poor shape – there were as little as 60 nodes active last year around this time. Since then the situation has only deteriorated – the jury is still out as to whether BlueMatt's doohicky actually helped or hindered while it was functional, but there's no argument that the network degraded YoY.

2. Who, according to your own preference, may be the NSA or the Antpool/F2pool cartel.

3. The A1 transaction wasn't broadcast and then included in a block – at the time it was broadcast, the block containing it had already been mined – it simply hadn't yet been shared with the rest of the plebs is all.

4. 51% means that out of a day's 144 blocks, one has 74, and consequently gains a 3 block advantage over a competitor chain every single day..It is true that the cartel does not generally wish to advertise its presence (yet), and so to date they've avoided major reorgs. Bear in mind however that it is also the case that the remainder minority is not united but fragmented – so they don't actually need to resort to major reorgs.