/1 Why is the credit card called โ๐ญ๐ก๐ ๐ฆ๐จ๐ฌ๐ญ ๐ฉ๐ซ๐จ๐๐ข๐ญ๐๐๐ฅ๐ product in banksโ? How does VISA/Mastercard make money?
The diagram below shows the economics of the credit card payment flow.
1. The cardholder pays a merchant $100 to buy a product.
/2 2. The merchant benefits from the use of the credit card with higher sales volume and needs to compensate the issuer and the card network for providing the payment service. The acquiring bank sets a fee with the merchant, called the โ๐ฆ๐๐ซ๐๐ก๐๐ง๐ญ ๐๐ข๐ฌ๐๐จ๐ฎ๐ง๐ญ ๐๐๐.โ
/3 3 - 4. The acquiring bank keeps $0.25 as the ๐๐๐ช๐ฎ๐ข๐ซ๐ข๐ง๐ ๐ฆ๐๐ซ๐ค๐ฎ๐ฉ, and $1.75 is paid to the issuing bank as the ๐ข๐ง๐ญ๐๐ซ๐๐ก๐๐ง๐ ๐ ๐๐๐. The merchant discount fee should cover the interchange fee.
/4 The interchange fee is set by the card network because it is less efficient for each issuing bank to negotiate fees with each merchant.
/5 5. The card network sets up the ๐ง๐๐ญ๐ฐ๐จ๐ซ๐ค ๐๐ฌ๐ฌ๐๐ฌ๐ฌ๐ฆ๐๐ง๐ญ๐ฌ ๐๐ง๐ ๐๐๐๐ฌ with each bank, which pays the card network for its services every month. For example, VISA charges a 0.11% assessment, plus a $0.0195 usage fee, for every swipe.
/6 6. The cardholder pays the issuing bank for its services.
Why should the issuing bank be compensated?
๐นThe issuer pays the merchant even if the cardholder fails to pay the issuer.
๐นThe issuer pays the merchant before the cardholder pays the issuer.
/7 ๐นThe issuer has other operating costs, including managing customer accounts, providing statements, fraud detection, risk management, clearing & settlement, etc.
Over to you: Does the card network charge the same interchange fee for big merchants as for small merchants?
1 - Collaboration Tools
Software development is a social activity. Learn to use collaboration tools like Jira, Confluence, Slack, MS Teams, Zoom, etc.
2 - Programming Languages
Pick and master one or two programming languages. Choose from options like Java, Python, JavaScript, C#, Go, etc.
3 - API Development
Learn the ins and outs of API Development approaches such as REST, GraphQL, and gRPC.
4 - Web Servers and Hosting
Know about web servers as well as cloud platforms like AWS, Azure, GCP, and Kubernetes
5 - Authentication and Testing
Learn how to secure your applications with authentication techniques such as JWTs, OAuth2, etc. Also, master testing techniques like TDD, E2E Testing, and Performance Testing
6 - Databases
Learn to work with relational (Postgres, MySQL, and SQLite) and non-relational databases (MongoDB, Cassandra, and Redis).
Twitter has enforced very strict rate limiting. Some people cannot even see their own tweets.
Rate limiting is a very important yet often overlooked topic. Let's use this opportunity to take a look at what it is and the most popular algorithms.
A thread.
#RateLimitExceeded
What is rate limiting? Rate limiting controls the rate at which users or services can access a resource. Here are some examples:
- A user can send a message no more than 2 per second
- One can create a maximum of 10 accounts per day from the same IP address
Fixed Window Counter
The algorithm divides the timeline into fixed-size time windows and assigns a counter for each window. Each request increments the counter by some value. Once the counter reaches the threshold, subsequent requests are blocked until the new time window begins
/1 What is the difference between โpullโ and โpushโ payments?
The diagram below shows how the pull and push payments work.
/2 ๐น When we swipe a credit/debit card at a merchant, it is a pull payment, where the money is sent from the cardholder to the merchant. The merchant pulls money from the cardholderโs account, and the cardholder approves the transaction.
/3 ๐น With Visa Direct or Mastercard Send, the push payments enable merchant, corporate, and government disbursements.
Step 1: The merchant initiates the push payment through a digital channel. It can be a mobile phone or a bank branch etc.
/2 The Netflix Engineering team selects a variety of databases to empower streaming at scale.
Relational databases: Netflix chooses MySql for billing transactions, subscriptions, taxes, etc. They use CockroachDB to support a multi-region active-active architecture.
/3 Columnar databases: Netflix primarily uses them for analytics purposes. They utilize Redshift and Druid for structured data storage, Spark and data pipeline processing, and Tableau for data visualization.