DEFAULT TIMESTAMP and system clock

[#1]

From the documentation

Columns declared with DEFAULT TIMESTAMP contain unique values so that applications can detect near-simultaneous updates to the same row. If the present timestamp value is the same as the last value, it is incremented by the value of the default_timestamp_increment option.

This all sounds reasonable, but what happens if the system clock is changed (for example set back due to a time server synchronization). Can this cause a situation where either

1. DEFAULT TIMESTAMP gives a value less than its previous value or worse
2. DEFAULT TIMESTAMP returns a value that is non-unique

This seems possible given the last sentence suggests that it is only compared against the previous value, so if the DEFAULT TIMESTAMP value does go backwards due to a clock change, it could conceivably produce the same value twice.

Thanks

[MCMartin]

If you want something unique from the database system use an autoincrement field or a GUID field. Or you can force uniqness of the timestamp field by declaring a unique index on it (anyway this may reject otherwise valid inserts 😉 ). Doing so would at least identify a system clock problem.