Bitcoin Forum

Could you explain: 4 months ago it took me 15 minutes to get 6 confirmations, now it is 2 hours+. It is temporary, or what? What is going on?
And how long does it take you to get 6 confirmations on a payment?
Thank you.

Maybe you should start paying fees?

It should average to roughly 10m each conf. However, because hashrate is rapidly increasing, it should be 6-10m, depending on how far beyond the last difficulty change we are.

It's always been on a 10m target. So, 15m is very unlikely (but possible), and 2h is unlikely (but very possible). Just some variance. :)

ETA: I misread -- I thought you meant 6 confs came in 2h, which'd be more normal.

I am paying fees, and yes, it is 3h / 1 of 6 confirmations now.

sounds stupid but try different address/wallet?

EDIT: even more stupid - maybe there's extra time of you turning on your btc client, and catching up to the blockchain involved?

Might be poor connection with other peers...

Blockchain's showing some slowness in solving lately... Last block solved 33m ago, penultimate 1h16m ago.

I measure time after all blocks are loaded. Load, then send coins. So it is not loading blocks.
8 connections.
Different addresses, but same wallet. I'll try another one.

So, how long does it take you, guys?

Could you give example tx ids?

Just standard address, generated by Bitcoin QT.

In the last 24 hours there have been a few blocks that took like an hour to be found. 

I have a tangential newby question:  Is each confirmation a repeated instance of a transaction?  I ask because I purchased my first every BTC two days ago via localbitcoins.com and immediately sent them to my blockchain.info.  By now, the confirmations are at 292, but when I look up my one transaction in the history, it is only listed as being part of one block.  So do N confirmations imply N instances of that transaction in N distinct blocks, or does that mean that that one block was passed around to various nodes N times?

Another question:  When I look up my transaction, why is it grouped with some other transfer of BTC from the same payer address as one transaction [e.g., one address sent me what I bought with case on Tuesday (minus the initial see from localbitcoins) along with some other amount to some other address]?

Transaction receives 1 confirmation when it appears in a valid mined block. Blockchain grows and each subsequent mined block adds 1 confirmation to your transaction. Transaction can appear only once in the blockchain, however sometimes blockchain may be forked, and only the longest fork survives. More confirmations your transaction has - more chances it is valid and you are in the main blockchain.


I know 2 possible reasons for that:

1) part of money (change) go back to the senders' address - that's a feature of Bitcoin protocol
2) sender can use sendmany transaction (thus sending money to multiple recipients in a single transaction to reduce fees)

Update: see https://en.bitcoin.it/wiki/Block_chain and the linked pages from bitcoin wiki

(1) So each successive mined block after the block containing your transaction increments your confirmation count by one because the non-occurence of a fork with any one of these successive blocks adds credibility to your transaction?

(2) Is a fork caused by an invalid transaction in a previous block, in which case a new block, with all of the transactions in the affected block sans the invalid transaction, is sent?

(3) How is block numbering sorted out when there is a fork?

I'll probably try to start answering from the last question.

(3) blocks are numbered sequentially, thus blockchain can't contain 2 blocks with the same number

(2) bitcoin mining is decentralized, fork can be caused by 2 independent miners who mined 2 versions of block with the same block number at about the same time. the one who generates & distributes the block quicker has more chances that his block will be part of the longer chain (that will survive).

(1) yes, kind of... more confirmations = less chances that your transaction will be discarded... because in order to discard it, a longer chain of blocks should be mined, and it is computationally expensive... one needs to have a higher computing power than the rest of the network in order to do so

that's my understanding of things.. I am not a bitcoin developer, so maybe I am inaccurate somewhere   

So why is six considered to be the magic number for when merchandise can be released or services provided?  At an average of 10 minutes per mined block, that would mean that forking events are sorted out in less than an hour?   ???

I don't know how it is done in detail, but I understand it the following way:

If there are 2 competing blocks with the same block number, then mining nodes decide which one should be included in the blockchain. Part of the network received one version of block, another part of the network received another version. So they work in parallel for some time. But when one of the parts generate one block on top of that conflicting block, it wins thus invalidating efforts of the other one (all miners switch to the longest chain). Thus if there are 2 confirmations, it should be more or less secure for small sums of money. But not very secure since sometimes due to attack or bug or just a rear coincidence competing forks could exist longer than 2 confirmations.  

6 is just a magic number, equivalent to 1 hour of hashing power of the whole network.

Merchants decide how many confirmations they require. Some merchants probably accept even 0-confirmations (for small sums of money from trusted buyers with a delay to detect if there is a competing block in the network or some other technical tricks). But if you are receiving large sums, e. g. thousands of bitcoins, it might be a good idea to wait for longer than 6 confirmations.

Single-block forks happen fairly often.  I haven't kept up on the numbers, but the last time I looked at the fork data it looked like an average of one single-block fork per 300 blocks, roughly every other day.  This corresponds to a double-block fork every 300² blocks, or roughly every other year.

Six confirmations is good insurance against honest (latency-based) chain forks.

In regards to confirmation times, people have to remember that the 10-minute target works out on average; so it will almost never be exactly 1 hour for 6 confirmations, especially with the hashing power increasing so much in the past several months.

Depending on exactly when the transactions of the OP happened, the first may have been just before a difficulty change when the average (for 24 hours) may have been 7-8 or more blocks/hour, while the second may have been after, and compounded by a period of bad luck.  Look at the current hashrate graph:  http://bitcoin.sipa.be/speed-small-lin-2k.png

A transaction that took place around midnight on 22 July (last peak before difficulty change) would likely have confirmations faster than one around midnight on 24 July (the dip right after the difficulty change).

I've observed longer confirmation times as well. Took over an hour to get a single confirmation yesterday night.