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I have been exploring bitcoin API and I found there is network fee for every transaction which is around 0.0001 but I noticed many trading and bitcoin related agencies doesn't charge any network fee at all for transfer between user on same Website/App. Few of which are cryptopia, Zebpay and localbitcoins.
Could someone help me understand that how they are able to transfer between wallet without any network fee.
Organizations that offer online wallets aren't obligated to handle transactions using the actual Bitcoin blockchain; they may instead choose to keep their own off-chain record of transactions between users. While faster and cheaper than on-chain transactions, this system is often less secure, especially since the transaction records are centralized.
Only when a user transfers Bitcoins between an external wallet would an organization utilize the blockchain; this is when a transfer would cost some network fee and take some time to process.
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Why does bitcoin have miners? Why don't the users mine their own blocks. I understand it may be to ensure the currency is traded, but in any non transaction blockchain case do you need miners or is it fine to let the users mine their own blocks?
I couldn't find any reason as to why bitcoin really needs miners other than for adding coin to the market.
The only distinction between a user and a miner is that a miner is doing computational work to get bitcoin, and a user is using bitcoin to make transactions. A user could easily do the computational work as well, but then they would just be a miner. The reason not everyone is a miner is because not everyone wants to do computational work, many just want to make transactions.
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I was recently asked the following question in an interview.
"How would you design a system to keep track of a million items at xyz.com ?
The xyz.com could update the prices maybe 2-3 times a day or once per month, so no guarentee on frequency.
Your system should show accurate prices for >95% of items at any given point of time and aim for 99%.
Also scale for 1billion items etc..
"
I asnwered along the lines of creating a distributed system app that would categorize items by priority (based on historical price fluctuations and 80/20 % rule etc) and do API calls more frequently for these.
But I was not allowed to use API calls.
I suggested scraping html content. (But the website can block my ip for such high load)
I basically want to know the resources that would help me anwering these type of questions. Prefer full length courses (Distributed systems ?) or books rather than quick-fix blogs.
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I'm student and i'm working on bachelor thesis. My app uses wcf and sql database. If I want to test the application I need to host it. I would like to host it on Azure, 90 free trial, but it needs verification with credit card. I'm worried about sharing my credit cards data. I want to ask you, if it's secure and after 90 I have to pay for it or not?
Thanks
The billing and credit card information is hosted and stored by Microsoft themselves — you can look into the security of their practices in detail, but I am sure that they are okay. As long as you delete your database before the 90 days is up, you won't need to pay anything. You can still keep your subscription, just make sure that you aren't using any services. For peace of mind, check your billing on a daily basis and make sure that nothing is being recorded as running.
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In the case of payment gateways, if the gateway is US-based and can only charge in dollars, but can charge foreign debit/credit cards, and you want to act on countries where the currency is not USD, and you can't/do not want to apply for a local payment gateway, what could you do, programming-wise?
I was thinking about converting the amount in USD to the the specific currency. Problem is:
I don't know where to get real-time accurate exchange-rate data
Not sure if I get the data from somewhere, if the client's card processor will actually charge that exact price
Do you guys know any best-practices for that? I think another way would be to just charge in dollars, and then let the client know that approximate amount in his/her local currency, but again, I'm not sure where to get an updated currency conversion.
Does any of you have gone through a similar scenario?
PS.: Paypal is not an option.
Any hints appreciated!
Currency conversion takes place by your customer's bank, so there's unfortunately no central market through which you can even make estimates.
There are some APIs that you can use to make an estimate, though it's mostly just a guess. If you use one of these, I would make sure to make it clear to your customers that the price may vary depending on their bank.
Overall, I've found the best practice is just to display your prices in the supported currency (e.g., USD) and mention to your customers that it might vary. As we continue to expand internationally, you can take advantage of our local currency offerings to make more exact charges.
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There are several posts on SO that point to sources for downloading historical stock quotes, but these are all for currently listed symbols. The resulting dataset suffers from survivorship bias. Is there any source of all historical data, including delisted companies, preferably for free/cheap? I've found a few sources, but they're usually hundreds of dollars or more, require installing using some Windows client software, or just are on sketchy-looking websites. (End-of-day data is fine - I'm sure asking for intraday bid/ask is too much.)
Where do these data resellers in turn get their data from? What is the original source archive of data? (Some of these datasets date back to the '50s, so I don't think the answer is "they just record it themselves.") Do they cut deals with exchanges / do the exchanges have/sell this? Does the data exist in any public records? Thanks!
Norgate Investor Services is the cheapest I've found, but it will run you hundreds of dollars ( but less than 1000 ). Their source is Standard & Poors.
QuantQuote has survivorship bias free historical stock data, but they only offer it in minute/second/tick resolution, and it costs $$. They also have free daily resolution data of the S&P500. It's too bad Yahoo doesn't keep stock data around after a stock gets delisted.