Re: Conflict Detection and Resolution

On Thu, Jun 6, 2024 at 5:16 PM Nisha Moond <nisha(dot)moond412(at)gmail(dot)com> wrote:

> >
>
> Here are more use cases of the "earliest_timestamp_wins" resolution method:
> 1) Applications where the record of first occurrence of an event is
> important. For example, sensor based applications like earthquake
> detection systems, capturing the first seismic wave's time is crucial.
> 2) Scheduling systems, like appointment booking, prioritize the
> earliest request when handling concurrent ones.
> 3) In contexts where maintaining chronological order is important -
> a) Social media platforms display comments ensuring that the
> earliest ones are visible first.
> b) Finance transaction processing systems rely on timestamps to
> prioritize the processing of transactions, ensuring that the earliest
> transaction is handled first
>

Thanks for sharing examples. However, these scenarios would be handled by
the application and not during replication. What we are discussing here is
the timestamp when a row was updated/inserted/deleted (or rather when the
transaction that updated row committed/became visible) and not a DML on
column which is of type timestamp. Some implementations use a hidden
timestamp column but that's different from a user column which captures
timestamp of (say) an event. The conflict resolution will be based on the
timestamp when that column's value was recorded in the database which may
be different from the value of the column itself.

If we use the transaction commit timestamp as basis for resolution, a
transaction where multiple rows conflict may end up with different rows
affected by that transaction being resolved differently. Say three
transactions T1, T2 and T3 on separate origins with timestamps t1, t2, and
t3 respectively changed rows r1, r2 and r2, r3 and r1, r4 respectively.
Changes to r1 and r2 will conflict. Let's say T2 and T3 are applied first
and then T1 is applied. If t2 < t1 < t3, r1 will end up with version of T3
and r2 will end up with version of T1 after applying all the three
transactions. Would that introduce an inconsistency between r1 and r2?

--
Best Wishes,
Ashutosh Bapat