> Here are some disadvantages to using a "trigger based" approach:
>
> 1) Triggers simply transfer individual data items when they
> are modified, they do not keep track of transactions.
> 2) The execution of triggers within a database imposes a performance
> overhead to that database.
> 3) Triggers require careful management by database administrators.
> Someone needs to keep track of all the "alarms" going off.
> 4) The activation of triggers in a database cannot be easily
> rolled back or undone.
Yes, points 2 and 3 are a given, although point 2 buys you the functionality
of transparent locking across all involved db servers.
Points 1 and 4 are only the case for a trigger mechanism that does
not use remote connection and 2-phase commit.
Imho an implementation that opens a separate client connection to the
replication target is only suited for async replication, and for that a WAL
based solution would probably impose less overhead.
Andreas
