Shard key

Choose a shard key.

Shard key

The shard key is the column that decides which shard a row goes to. A good shard key spreads data evenly and keeps most queries within a single shard.

CREATE TABLE orders (id INT, created_at DATE)
PARTITION BY RANGE (created_at);

The shard key drives distribution.

The table orders is created.

Shard key — details

A bad shard key (say, only true/false) piles data on two shards. A date shard key heaps old data on one shard. Customer ID usually spreads best.

Exercise Shard key

Partition the orders table by date range with PARTITION BY RANGE (created_at).

Show example solution

CREATE TABLE orders (id INT, created_at DATE) PARTITION BY RANGE (created_at);

Test yourself

Range partition

PARTITION BY ____ (created_at)

Show answer

PARTITION BY RANGE (created_at)

Shard key: match the terms

shard key

shard key
even

even
date

date
customer

customer
What makes a good shard key?
- It never changes
- It spreads data evenly
- It has a single value
- It is historical
Show answer

It spreads data evenly — A good shard key spreads data evenly.

Next lesson: Summary - Replication and sharding

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