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 provisioning etc...

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 for transactions"".

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 or clients.




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