Choosing the Right Indexing Method (7/7)

Congratulations on making it to the final day! Over the past week, we’ve learned about flat search, HNSW, IVF, and PQ. Today, let’s put it all together and learn how to pick the right method for your needs.

Quick Recap: What We’ve Learned

Think of these methods like different ways to find a book in a library:

• Flat Search: Check every book one by one. Slow but always finds exactly what you need.
• HNSW: Follow a map of connected books to quickly navigate to the right area.
• IVF: Books are organized into sections. Go to the right section first, then search there.
• PQ: Books are labeled with short codes instead of full descriptions. Uses less space but slightly less precise.

The Simple Decision: Three Questions

When choosing a method, just ask yourself three questions:

Question 1: How much data do you have?

Question 2: Do you need exact results or is “close enough” okay?

• Need 100% exact matches? → Use Flat Search
• 95% accuracy is fine? → Use HNSW (fast and accurate)
• 90% accuracy is acceptable? → Use IVF-PQ (saves memory)

Question 3: How much computer memory do you have?

• Plenty of memory? → HNSW gives best results
• Limited memory? → IVF-PQ compresses data to save space

Real-World Examples (Simplified)

Example 1: A Small Online Store

You have 10,000 products. Which method?

Answer: Flat Search. With only 10,000 items, searching through all of them is fast enough. Keep it simple!

Example 2: A Music App with Recommendations

You have 500,000 songs and want to find similar songs quickly.

Answer: HNSW. It’s fast, accurate, and handles this size well.

Example 3: A Large Image Database

You have 50 million images and limited server memory.

Answer: IVF-PQ. It compresses the data so you don’t run out of memory.

The Trade-Off Triangle

Every indexing method balances three things:

        SPEED
          /\
         /  \
        /    \
       /      \
      /________\
  ACCURACY    MEMORY

• Flat Search: High accuracy, low memory, but slow
• HNSW: Fast and accurate, but uses more memory
• IVF-PQ: Fast and low memory, but slightly less accurate

You can’t have all three perfectly – you have to choose what matters most for your project.

Simple Rules to Remember

1. Start Simple: Begin with flat search. Only switch to fancier methods when you actually need to.

2. Test First: Don’t guess which method is best. Try a few and see which works for your data.

3. Good Enough is Good Enough: If 95% accuracy meets your needs, don’t over-complicate things trying to get 100%.

4. Memory Matters: If your computer runs out of memory, accuracy doesn’t matter because nothing will work!

Quick Reference Card

What You’ve Learned This Week

Day 1: What searching and indexing means Day 2: Flat search – the simple approach Day 3: Approximate search – trading accuracy for speed Day 4: HNSW – navigating through connected data Day 5: IVF – organizing data into clusters Day 6: PQ – compressing data to save space Day 7: How to choose the right method (today!)

Final Thoughts

Choosing an indexing method doesn’t have to be complicated. For most beginners:

• Small project? Use flat search
• Need speed? Use HNSW
• Running out of memory? Use IVF-PQ

The best method is the one that solves YOUR problem. Don’t overthink it – start simple, measure results, and adjust if needed.

Thanks for joining this 7-day journey into indexing methods! You now understand the fundamentals that power search engines, recommendation systems, and AI applications everywhere.