You shard view counts by video_id. One viral video now gets 200,000 writes a second, far more than one shard can take. What is the usual fix?

Options

• ✗ Shard by user_id instead
• ✗ Add more shards; the hash spreads the load
• ✓ Split the hot key: write to video_id#0 … video_id#N and sum them on read Correct
• ✗ Put the counter in a bigger database

Why

More shards do not help: one key always hashes to one shard. Salting the key spreads its writes over N shards, and reads add up N small counters (or a cache holds the total).

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