Re: Why we lost Uber as a user

Stephen Frost <sfrost@snowman.net> writes:
> With physical replication, there is the concern that a bug in *just* the
> physical (WAL) side of things could cause corruption.

Right.  But with logical replication, there's the same risk that the
master's state could be fine but a replication bug creates corruption on
the slave.

Assuming that the logical replication works by issuing valid SQL commands
to the slave, one could hope that this sort of "corruption" only extends
to having valid data on the slave that fails to match the master.
But that's still not a good state to be in.  And to the extent that
performance concerns lead the implementation to bypass some levels of the
SQL engine, you can easily lose that guarantee too.

In short, I think Uber's position that logical replication is somehow more
reliable than physical is just wishful thinking.  If anything, my money
would be on the other way around: there's a lot less mechanism that can go
wrong in physical replication.  Which is not to say there aren't good
reasons to use logical replication; I just do not believe that one.
        regards, tom lane