On 07/07/2016 05:14 PM, Simon Riggs wrote:
I would much rather see more brain power put into pg_upgrade or in
place upgrades than logical replication (as a upgrade solution).
Why is that?
First, let me state that I don't have a problem with logical replication
as an upgrade solution. I have used one form or another many times. I
have also used pg_upgrade and will use pg_upgrade every single time I
can over replication (even pg_logical which is reasonably simple) if I
can. *KISS* is the mantra.
I certainly think logical replication has an absolute place (especially
if upgrading from something like 9.2 -> 9.5). I just don't think it is
as useful (generally) as a solid pg_upgrade or in-place upgrade solution.
We have had logical replication as a solution for over a decade. First
there was slony then londiste and then others. They all suffered from
various issues and limitations.
* Horrible overhead
* Long running transaction
* Need for lots of extra space
It is true that something like pg_logical doesn't suffer from those
three things but it does suffer from others:
* No DDL - Agreed, not "required" but certainly a very nice feature.
* Lack of simplicity
Users, like simple. It is one of the key reasons there is a migration to
the cloud, simplicity. Everything from scaling, to pricing, to
If I take a step back and say to myself, "What would *really* rock in
terms of PostgreSQL upgrades?" The answer is pretty simple:
apt-get update; apt-get upgrade;
service postgresql upgrade;
Which would pass a flag to "insert technology here" that started
PostgreSQL in a mode that told it, "Hey, you are going to need to check
a few things and probably modify a few things before you enter "ready
I am fully aware that what I am saying is not easy. There are a whole
ton of issues (what if we are replicating to a slave?).
Anyway, that's why. I am by far more a consultant than an engineer now
and I can only relay what I run into when I speak either at conferences
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