All 7 Strings & Bitmaps in Redis questions
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What is the Redis string data type, and what kinds of values can it actually store? How do you atomically increment and decrement a numeric value stored as a Redis string? What are Redis bitmaps, and how do they let you efficiently work with individual bits within a string? How do you use the SETRANGE and GETRANGE commands to work with a specific portion of a Redis string without affecting or retrieving the rest of it? How would you use bitmap operations like BITOP to combine multiple daily activity bitmaps and answer questions like how many users were active on both of two specific days? What are practical real world applications where using bitmaps provides a significant memory advantage over alternative approaches like sets?
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Redis › Strings & Bitmaps in Redis

How do you count the number of set bits within a bitmap, and how is this useful for analytics purposes?

Intermediate

Answer

You use the BITCOUNT command, which returns the total number of bits set to one within the specified range of a string, letting you efficiently calculate things like how many unique users were active on a specific day, since each active user's bit was set to one within that day's bitmap.
BITCOUNT user_active:2026-09-07
Real-world example An analytics dashboard displays the total number of active users for each day by running BITCOUNT against that day's bitmap, getting an accurate count without needing to store or iterate through an actual list of user identifiers.

Common follow-ups: How does BITCOUNT performance scale with the size of the bitmap?;Can you count bits within just a specific portion of a bitmap rather than the entire thing?

HyperLogLog in Redis;Redis Memory Optimization
All 7 Strings & Bitmaps in Redis questions