[Bucardo-general] bucardo internals and updates

[sym39]

Hello all,

We are using bucardo in multi master mode (all databases are "source" 
database) to replicate our technical database. In this configuration, 
there are 2 machines: one has the slave role (it does not update the 
tables as long as it is the slave) and other is master (it updates the 
tables)
For one of the table named events, the master may add or remove or 
updates rows. On both the master and the slave, we have built a system 
based on the postgres NOTIFY to act accordingly to those modifications 
to quickly detect changes without polling the events table.

1) About rows updates:
I understand that lines updates are replicated on the slave by first 
removing all impacted lines then by adding the updated (master) lines. I 
guess this is done inside a transaction, so I guess it is never possible 
to have one race condition that would show the temporary deleted lines 
as deleted lines while getting the content of the events table "at the 
same time" it is updated by bucardo ? In other words, after an update on 
the master, a single "select * from events" on the slave will never 
display less lines than there are on the master even if the select is 
done "in the middle of" the bucardo replication job.
  Am I right ?

2) About notifications, add/remove and always trigger:
Each time a modification (add/remove/update) is done on a row, a trigger 
is called and notifies about the change. To make sure that notifications 
are sent on the slave, we have updated the triggers as always trigger.
This works for add and remove, but as an update is done with delete 
followed by copy, we have some difficulties to make the distinction 
between a "real" add, a "real" remove and an update that leads to 
remove/add events.
Any ideas about that?

Thanks and regards,
Sylvain