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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 count the number of set bits within a bitmap, and how is this useful for analytics purposes? 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? What are practical real world applications where using bitmaps provides a significant memory advantage over alternative approaches like sets?
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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?

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Answer

You use BITOP with the AND operation to combine two bitmaps into a new one where only bits set in both original bitmaps remain set, and then run BITCOUNT on that resulting combined bitmap to get the count of users active on both days, giving you powerful analytical capabilities using very simple, efficient bitwise operations.
BITOP AND result_key user_active:2026-09-06 user_active:2026-09-07
BITCOUNT result_key
Real-world example A product analytics team calculates how many users were active on both Saturday and Sunday by combining the two days' bitmaps with a bitwise AND operation, then counting the resulting set bits, all using extremely memory efficient bitmap operations.

Common follow-ups: What other bitwise operations besides AND does BITOP support?;How does this approach scale for calculating activity across many different days at once?

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All 7 Strings & Bitmaps in Redis questions