The auto-increment ID feature in TiDB is only guaranteed to be automatically incremental and unique but is not guaranteed to be allocated sequentially. Currently, TiDB is allocating IDs in batches. If data is inserted into multiple TiDB servers simultaneously, the allocated IDs are not sequential. When multiple threads concurrently insert data to multiple tidb-server instances, the auto-increment ID of the later inserted data might be smaller. TiDB allows specifying AUTO_INCREMENT for the integer field, but allows only one AUTO_INCREMENT field in a single table. For details, see Auto-increment ID and the AUTO_INCREMENT attribute.