why lightning change table auto_increment?为什么lightning会修改自增值的大小？

[sandy20140407]

log:
[INFO] [restore.go:1253] ["import and cleanup engine completed"] [engineTag=test.favfav:-1] [engineUUID=9c824252-d150-5902-a2c0-02d2f26ebf6c] [takeTime=8.515710692s] []
[INFO] [tidb.go:232] ["alter table auto_increment start"] [table=test.favfav] [auto_increment=1567203009]

question:
why lightning change the auto_increment value before checksum? And the new value will be so big that would lead to long gap between max(primary id) and next new rows.
lightning 在导入数据结束，checksum前会修改自增值，如果表数据很大，新的自增值和实际的当前最大ID间的距离会非常大，有字段溢出的风险。