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Software Engineering Concept

Fractional Indexing

JourneySoftware engineering Statuslearning Tags
  • collaboration
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A technique for maintaining ordered lists in distributed systems without reindexing.

How It Works ​

  • Each item's position is a fraction between 0 and 1 (exclusive).

  • Items are sorted by their position values.

  • To insert between two items, set the new item's position to the average of their positions.

  • No other items need to be updated (no reindexing).

Where It Appears ​

  • Figma uses fractional indexing to order children within a parent object.

  • The parent link and position are stored as a single property so they update atomically.

Tradeoffs ​

  • Positions can lose precision after many insertions (fractions get very long).

  • In practice, periodic rebalancing or using string-based fractional indices avoids this.