-------------------------------------
| id   | type   |object| timestamp |
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| 1    | create | A    | 2019-1-1  |
| 2    | create | A    | 2019-1-2  |
| 3    | delete | A    | 2019-1-2  |
| 4    | create | B    | 2019-1-1  |
| 5    | delete | B    | 2019-1-2  |
| 6    | create | A    | 2019-1-3  |
| 7    | create | B    | 2019-1-4  |
| 8    | create | C    | 2019-1-5  |
-------------------------------------