Sharding Strategies: How to Split the Map

As we learned in the last lesson, Sharding allows us to store massive amounts of data by splitting it across multiple servers. But how you split that data determines how fast your search will be.

If you split it poorly, one server will do all the work while the others sit idle. If you split it well, you get perfect parallel performance.

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1. Random / Round-Robin Sharding

The simplest method. As data comes in, you put the first vector in Shard A, the second in Shard B, and so on.

• Pros: Perfectly balanced data storage.
• Cons: Every query must hit every shard. This is the "Scatter-Gather" bottleneck.

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2. Metadata / Tenant Sharding

If you are building a SaaS app, you might shard by user_id or tenant_id.

• Concept: All vectors for "Company A" live on Shard 1.
• Pros: Massive performance gain. When Company A queries, the coordinator only hits Shard 1.
• Cons: If Company A grows 100x bigger than Company B, Shard 1 will run out of space ("Hot Shards").

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3. Geographic / Latency Sharding

In global applications, you might shard by Region.

• Concept: Embeddings from US users stay in US data centers; EU stay in EU.
• Pros: Reduced network latency and easier compliance with data laws (GDPR).

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4. Implementation: The Consistent Hashing Pattern

To prevent "Hot Shards," distributed systems use Consistent Hashing.

Shard_ID = Hash(Vector_ID) % Total_Shards

This ensures that even if your IDs are sequential, they are spread evenly across the cluster. When you add a new machine, consistent hashing minimizes the amount of data that needs to be moved around.

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5. Summary and Key Takeaways

1. Balance is Key: Poorly sharded data leads to "Hot Shards" that crash your system.
2. Tenant Isolation: If your queries almost always filter by a specific field (like user_id), consider sharding by that field.
3. Scatter-Gather Costs: Remember that the more shards you have, the more network overhead you create for every global search.
4. Grow with Care: Re-sharding an active production database is extremely difficult. Always plan for 2x to 5x your current data volume.

In the next lesson, we’ll look at Replication—how we ensure our shards don't lose data.

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Congratulations on completing Module 15 Lesson 2! You are now a data partitioning architect.