# What causes writes hotspot (A)


![left](./student-guide/diagram/21-Data-organization-model-01-01.png)


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Taking row data as an example, TiDB assigns a TableID to each table, an IndexId for each index, and a RowID for each row (by default, if the table uses int Primary Key, the value of the Primary Key will be used as the RowID). Where tableId is unique across the cluster, indexID/rowID is unique within the table, and these IDs are int64 type.

Each row of data is encoded according to the following rules

```
Key-Value pair：
Key: tablePrefix{tableID}_recordPrefixSep{rowID}
Value: [col1, col2, col3, col4]
```

Where TablePrefix and RecordPrefixSep for Key are specific string constants used to distinguish other data in the KV space.