1. Number of connections are controlled by MySQL configuration parameter
max_connections.
2. Use caching in your application and MySQL. Design your DB in such a way which requires minimum JOINs to fetch data. This is also known as denormalization. Write optimize queries, avoid
SELECT * sort of quereis and properly index your data.
3. They adopt all the techniques which are mentioned above and as well as some others which is not mentioned here
They have multiple web servers and database servers, you can say server farms.
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