[Bucardo-general] Questions on `add sync` params

[Greg Sabino Mullane]

> I've still no idea WTF makedelta is or why one would want to use it, though

It works for B4 (and has been used in production), but is not working 
yet for B5. In a nutshell, it creates dummy entries so that a table 
can be updated by more than one sync. So say I have a sync x that 
does multimaster between databases A and B. I also have a sync y 
that does a source->target sync from database B to C. When someone 
changes a rows on table foobar on database A, Bucardo pushes that 
change out to B.foobar via the x sync. However, because we disable 
all triggers and rules when we do the DELETE/COPY, the bucardo_delta 
table for B.foobar will NOT have the primary keys we just changed. 
Thus, as far as sync y is concerned, B.foobar has no changes and 
thus they do not get pushed out to C (all of these could also be source-target, 
source-source, source-source-target, or whatever).

We cannot simply leave those triggers on, else we get into an infinite loop 
as A.foobar adds a record to B, and then the same sync sees that B has a 
change and pushes it out to A, which then records the change...

Thus, makedelta: it adds an entry in bucardo_delta for that table, but 
also adds an entry to bucardo_track. In the example above, it will 
add a bucardo_delta entry for B.foobar, and a matching bucardo_track 
entry so that sync x thinks it has already processed that change (which 
it has).

-- 
Greg Sabino Mullane greg at endpoint.com
End Point Corporation
PGP Key: 0x14964AC8
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