Deploying DDLs
Replicating just one table is clearly not enough for a productive application. Also, there is usually no way to ensure that the data structure never changes. At some point, it is simply necessary to deploy changes of the data structures (so-called DDLs).
The problem now is that Slony relies heavily on triggers. A trigger can fire when a row in a table changes. This works for all tables, but it does not work for system tables. So, if you deploy a new table or happen to change a column, there is no way for Slony to detect that. Therefore, you have to run a script to deploy changes inside the cluster to make it work.
Tip
PostgreSQL 9.3 and beyond have some basic functionality to trigger DDLs, but that is not enough for Slony. However, ...
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