How to Cancel Unconfirmed Bitcoin Transactions

16 Jun
2016

unconfirmed-bitcoin-transaction

With the recent spike in the price of Bitcoin the number of unconfirmed transactions has increased significantly yet again and the Bitcoin blocks are getting closer and closer to being full. This essentially slows down transactions on the network and in order to ensure that your transaction is being processed faster you need to increase the fee over the standard recommended one. While this may be just fine for larger BTC transfers with fewer inputs, if you want to make a small transaction of few Bitcoin cents or a large one with a lot of inputs the network fees can get quite high. If the fee is not large enough and the waiting list is big you can easily end up with your transaction not getting confirmed and included in a block for over a day and that usually causes a problem, especially if you are paying for something in BTC. The solution would be to just cancel any unconfirmed transaction that did not go through for over 24 hours and it is not that hard to do it actually, although the process itself may require some time.

bitcoin-qt-zapwallettxes

Cancelling stuck Bitcoin transaction sent from your local BTC wallet requires you to run the qt wallet client with a special option that would remove all pending transactions that are not included in the blockchain. You need to run bitcoin-qt.exe (or the respective qt executable file depending on the OS you are using) with the -zapwallettxes parameter, but before running it make sure you backup your wallet.dat file. This will take some time as it will initiate a blockchain rescan, so be prepared to wait until the process finishes and do not forget to remove the extra parameter the next time you run your wallet as it is not needed anymore. Reports from Aktien Kaufen und Verkaufen state that as a result you will be able to initiate a new transaction with the unspent coins and by increasing the network fee you pay you should be able to move them faster and have the transaction confirmed this time. You will be essentially double spending your Bitcoins, but the second transaction you initiate will cancel out the earlier one. You cannot successfully double spend Bitcoins unless you control more than half of the Bitcoin network, so no worries here. The only thing you will be able to do is free up your coins that were stuck in an unconfirmed transaction for a long time and then be able to initiate a new transaction to send them successfully this time.

Do note that although we are giving this example for Bitcoin, it should work on many other altcoins as well that are based on a more recent forked Bitcoin wallet code as the option we use here is not included in the earlier version of the Bitcoin client. There are some more complex alternatives for performing the same thing described here if your wallet does not support the zapwallettxes option, so you are not out of luck in such cases either. You can do the same thing with the Python-based tool called Pywallet as an alternative to using the qt wallet method described here.

Nvidia GeForce GTX 1080 Founders Edition Power Usage for Crypto Mining

15 Jun
2016

gtx-1080-founders-edition-gpu-black

Time for a quick look at the power usage of the GeForce GTX 1080, the reference design from Nvidia that has a TDP of 180W set by the manufacturer, making it pretty energy efficient for the performance it provides for crypto currency mining. We are checking the situation with the different algorithms apart from Ethereum, because we already know that the GTX 1080 is far from great choice for Ethereum mining.

gtx-1080-power-usage

The GTX 1080 Founders Edition TDP limit of 180 Watt has a power limiter that can give you up to extra 20% increase, moving the slider to increase the maximum available power to be used by the GPU. This can help you get some extra hashrate for the algorithms that max out the 180 Watt TDP of the GPU and as you can see these are actually quite a few. The non reference versions of GTX 1080 should come with higher TDP limits and even higher factory clocks, so they should be able to achieve even more performance as they will be able to keep higher boost frequency of the GPU while mining. Then again you might also want to lower the power limit in order to reduce the power usage and get an even better hashrate per Watt of power used, but for that you might have to also play with the voltage of the GPU for best results and also the clocks.

In the table above you can see that Neoscrypt and Lyra2Re are far from maxing out the TDP of the GTX 1080, the reason for that is that they do not perform that well in terms of hashrate, so some optimizations for them might help give you better performance. Other than that the power usage is high and the hashrate you get is seriously increased as compared to the previous generation of Nvidia GPUs, so performance per Watt for the GTX 1080 is actually great in most algorithms for crypto mining.

Testing the Nvidia GeForce GTX 1080 Founders Edition for Crypto Mining

14 Jun
2016

nvidia-geforce-gtx-108-founders-edition

We continue our series of tests of the new Nvidia GeForce GTX 1080 Founders Edition (reference design) for crypto currency mining after yesterday we have checked the situation for mining Ethereum with the new Pascal GPUs and have seen the not so great results. Ethereum and the Dagger-Hashimoto algorithm it uses is still doing better on AMD GPUs, but Ehereum mining is set to end at some point with the altcoin switching to PoS only and the forks that use the same algorithm are not yet providing a real alternative. So with the growing difficulty and the switch to PoS at some point in probably less than a year you should also be interested in how the GTX 1080 performs in other new GPU mineable algorithms as well as in the more popular ones that. This is the reason we are now going to compare the GeForce GTX 1080 Founders Edition with GTX 980 Ti and GTX 970 to see the difference in terms of performance in other algorithms as well. As you will probably see the GTX 1080 does provide a nice performance boost compared to the two other older generation alternatives, but with its currently high price even the power saving does not make it great option for building multi-GPU mining rigs for the moment. The more interestingly priced GTX 1070 will most likely be the better choice for building 6 GPU mining rigs succeeding the GTX 970 as the best Nvidia-based GPU for crypto mining, though we are yet to test the 1070 in order to confirm that.

gtx-1080-hashrate-results

The ccminer forks we have used for testing:
– Blakecoin (Blake256-8rounds), Decred (Blake256-14rounds), Vcash (Blake256-8rounds) ccminer
– Lyra2REv2 ccminer
– X11evo ccminer
– All other algorithms

Tests were done under Windows 7 with already existing ccMiner releases that are not compiled with CUDA 8.0 and with support for Compute 6.1 that the GTX 1080 uses, though without optimizations specific for GTX 1080 or the Pascal architecture in general we are probably not going to see much of a difference. Anyway, we do have planned to do additional testing comparing the difference in terms of performance with existing ccMiner forks compiled with CUDA 8.0 and Compute 6.1 against the results here achieved with CUDA 6.5/7.5 and Compute 5.2 releases that were tested here.

We had almost problem-free experience testing the above algorithms on the GTX 1080, though there are some things that we need to note. For example the Nist5 default intensity (21?) was crashing the miner, so tested with 20 where it was working fine. The very low Neoscrypt performance on the GTX 1080 is because the algorithm probably needs special optimizations to take advantage of the GPU. The Lyra2RE performance was not that much faster on the GTX 1080 as compared to GTX 980 Ti, so here some optimizations will most likely result in increased performance. Note that we have also tested X11, though now that is has moved to the ASIC phase you probably won’t want to GPU mine it anyway.

What is clearly seen from the comparison above is that the new GTX 1080 performs about twice as fast (on average) than a single GTX 970 and we are using Gigabyte Windoforce 970 OC GPU comparing to stock 980 Ti and GTX 1080. The GTX 1080 uses about the same power as a single GTX 970, but offers twice the performance, but the real issue here is the price at the moment. If the GTX 1080 was about twice the price of GTX 970 it might’ve been an interesting option for miners that are currently using Nvidia GTX 970 mining rigs, but it is unfortunately more like 2.5 and not two times. Comparing the GTX 1080 to the GTX 980 Ti shows an average performance advantage of almost 50% in favor of the GTX 1080, with not that great price difference between the two cards (the GTX 1080 is about 30% more expensive). So definitely no point in going for GTX 980 Ti instead of GTX 1080 for mining, though still both cards are not the best choice for multi-GPU mining rigs, then again if you are buying just a single GPU for gaming and want to also mine with it when not gaming the GTX 1080 might be much more interesting that for use on multi-GPU mining rigs.

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