What is sharding and what is it used for? How to choose a sharding key for taxi service tables (drivers, customers, orders)?

Sharding is a method of horizontally partitioning data into parts (shards) that are stored on different servers or databases. This allows for system scalability, improved performance, and management of large data volumes.

For a taxi service, the choice of sharding key depends on the nature of the data and queries:

• Drivers: can be sharded by region or city, as drivers usually operate within specific geographic zones.
• Customers: can also be sharded by region or by customer ID if the load is evenly distributed.
• Orders: often sharded by date or by customer ID to localize queries about order history.

Example: if you have a database where each shard is responsible for a specific city, then the sharding key is the city or its code. This allows quick retrieval of drivers and orders in the required region.

It is important to choose a key that:

• Distributes load evenly across shards.
• Minimizes cross-shard queries.
• Matches data access patterns.

For example, if sharding by customer ID, all orders and customer data will be on one shard, which is convenient for order history queries.