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Aug 11 โ€ข 9 tweets โ€ข 3 min read
/1 Why is the credit card called โ€œ๐ญ๐ก๐ž ๐ฆ๐จ๐ฌ๐ญ ๐ฉ๐ซ๐จ๐Ÿ๐ข๐ญ๐š๐›๐ฅ๐ž 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 โ€œ๐ฆ๐ž๐ซ๐œ๐ก๐š๐ง๐ญ ๐๐ข๐ฌ๐œ๐จ๐ฎ๐ง๐ญ ๐Ÿ๐ž๐ž.โ€
/3 3 - 4. The acquiring bank keeps $0.25 as the ๐š๐œ๐ช๐ฎ๐ข๐ซ๐ข๐ง๐  ๐ฆ๐š๐ซ๐ค๐ฎ๐ฉ, and $1.75 is paid to the issuing bank as the ๐ข๐ง๐ญ๐ž๐ซ๐œ๐ก๐š๐ง๐ ๐ž ๐Ÿ๐ž๐ž. 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 ๐ง๐ž๐ญ๐ฐ๐จ๐ซ๐ค ๐š๐ฌ๐ฌ๐ž๐ฌ๐ฌ๐ฆ๐ž๐ง๐ญ๐ฌ ๐š๐ง๐ ๐Ÿ๐ž๐ž๐ฌ 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?

๐Ÿ”นThe issuer pays the merchant even if the cardholder fails to pay the issuer.

๐Ÿ”นThe issuer pays the merchant before the cardholder pays the issuer.
/7 ๐Ÿ”นThe 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?
/8 I hope you've found this thread helpful.

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More from @alexxubyte

Aug 10
/1 Why is single-threaded Redis so fast?

There are 3 main reasons, as shown in the diagram below.

If you prefer video, you can watch our YouTube video here โ‡ฉ

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If you prefer text, keep reading:
/2 1. Redis is a RAM-based database. RAM access is at least 1,000 times faster than random disk access.

2. Redis leverages IO multiplexing and single-threaded execution loop for execution efficiency.

3. Redis leverages several efficient lower-level data structures.
/3 Over to you: Another popular in-memory store is Memcached. Do you know the differences between Redis and Memcached?
Read 5 tweets
Aug 9
1. How do video live streamings work on YouTube, TikTok live, or Twitch? The technique is called live streaming.

Livestreaming differs from regular streaming because the video content is sent via the internet in real-time, usually with a latency of just a few seconds.
2. The diagram below explains what happens behind the scenes to make this possible.

Step 1: The raw video data is captured by a microphone and camera. The data is sent to the server side.
3. Step 2: The video data is compressed and encoded. For example, the compressing algorithm separates the background and other video elements. After compression, the video is encoded to standards such as H.264.

The size of the video data is much smaller after this step.
Read 13 tweets
Aug 9
1. Twitter and Reddit support NFT (Non-Fungible Token) profile pictures. Do you know what the differences between NFT profile pictures and regular profile pictures are?

The diagram below shows how NFT and regular images differ.
2. ๐‘๐ž๐ ๐ฎ๐ฅ๐š๐ซ ๐ฉ๐ซ๐จ๐Ÿ๐ข๐ฅ๐ž pic
๐Ÿ”นStep 1: The user uploads a profile picture, and this request goes to the user service

๐Ÿ”นStep 2: The picture is stored in an object store, like Amazon S3. A URL is generated to visit the file

๐Ÿ”นStep 3: The pictureโ€™s metadata is stored in DB
3. ๐๐…๐“ ๐ฉ๐ซ๐จ๐Ÿ๐ข๐ฅ๐ž image

๐Ÿ”นStep 1: To understand the process, we should know what smart contracts are. Smart contracts are programs deployed and stored on blockchains. They are self-executing when predetermined conditions are met. This is when an NFT is โ€œminted.โ€
Read 12 tweets
Aug 5
1. Digital wallet in ๐ญ๐ซ๐š๐๐ข๐ญ๐ข๐จ๐ง๐š๐ฅ ๐›๐š๐ง๐ค๐ฌ vs wallet in ๐›๐ฅ๐จ๐œ๐ค๐œ๐ก๐š๐ข๐ง

How does blockchain change digital wallets? Why does VISA invest in blockchains? A thread.

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2. ๐ˆ๐ง ๐›๐š๐ง๐ค๐ข๐ง๐  ๐ฌ๐ฒ๐ฌ๐ญ๐ž๐ฆ๐ฌ
๐Ÿ”นDeposit process: Bob goes to Bank of America (BoA) to open an account and deposit $100. A new account B1234 is created in the wallet system for Bob. The cash goes to the bankโ€™s vault and Bobโ€™s wallet now has $100.
3. If Bob wants to use the banking services of Citibank (Citi,) he needs to go through the same process all over again.
Read 11 tweets
Aug 4
1. How do we build a simple ๐œ๐ก๐š๐ญ ๐š๐ฉ๐ฉ๐ฅ๐ข๐œ๐š๐ญ๐ข๐จ๐ง using ๐‘๐ž๐๐ข๐ฌ?

The diagram below shows how we can leverage the pub-sub functionality of Redis to develop a chat application.
2. ๐Ÿ”นStage 1: Connection Initialization
Steps 1 and 2: Bob opens the chat application. A web socket is established between the client and the server.
3. Steps 3 and 4: The pub-sub server establishes several connections to Redis. One connection is used to update the Redis data models and publish messages to a topic. Other connections are used to subscribe and listen to updates for topics.
Read 10 tweets
Aug 3
/1 Algorithms you should know series for System Design.

๐€๐ฅ๐ ๐จ๐ซ๐ข๐ญ๐ก๐ฆ 1: ๐‚๐จ๐ง๐ฌ๐ข๐ฌ๐ญ๐ž๐ง๐ญ ๐‡๐š๐ฌ๐ก๐ข๐ง๐ 

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If you prefer text, keep reading: Image
/2 What do Amazon DynamoDB, Apache Cassandra, Discord, and Akamai CDN have in common?

They all use consistent hashing. Letโ€™s dive right in.
/3 ๐–๐ก๐š๐ญโ€™๐ฌ ๐ญ๐ก๐ž ๐ข๐ฌ๐ฌ๐ฎ๐ž ๐ฐ๐ข๐ญ๐ก ๐ฌ๐ข๐ฆ๐ฉ๐ฅ๐ž ๐ก๐š๐ฌ๐ก๐ข๐ง๐ ?

In a large-scale distributed system, data does not fit on a single server. They are โ€œdistributedโ€ across many machines. This is called horizontal scaling.
Read 13 tweets

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