# Index Design
+ Writes of a transaction in the Percolate model may have a Primary Key and multiple Secondary Keys
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We know the TiDB data writing model. Drawing on Google's Percolate paper, the self-implemented two-stage submission model. In the Percolate model, one thing is written with one Primary Key and multiple Secondary Keys, so in general, Index data is updated It is submitted as an update as a secondary key to ensure that the data is consistent with the index