About a year ago, we published PostgreSQL 10 with support for native logical replication. One of the uses of logical replication is to allow low- or no-downtime upgrading between PostgreSQL major versions. Until now, PostgreSQL 10 was the only PostgreSQL release with native logical replication, so there weren't many opportunities for upgrading in this way. (Logical replication can also be used for moving data between instances on different operating systems or CPU architectures or with different low-level configuration settings such as block size or locale -- sidegrading if you will.) Now that PostgreSQL 11 is near, there will be more reasons to make use of this functionality.
Let's first compare the three main ways to upgrade a PostgreSQL installation:
pg_dump and (more…)
I've started to write about the tool (pglupgrade) that I developed to perform near-zero downtime automated upgrades of PostgreSQL clusters. In this post, I'll be talking about the tool and discuss its design details.
You can check the first part of the series here: Near-Zero Downtime Automated Upgrades of PostgreSQL Clusters in Cloud (Part I).
The tool is written in Ansible. I have prior experience of working with Ansible, and I currently work with it in 2ndQuadrant as well, which is why it was a comfortable option for me. That being said, you can implement the minimal downtime upgrade logic, which will be explained later in this post, with your favorite automation tool.
Further reading: Blog posts Ansible Loves PostgreSQL , PostgreSQL Planet in Ansible Galaxy and (more…)
Last week, I was at Nordic PGDay 2018 and I had quite a few conversations about the tool that I wrote, namely pglupgrade, to automate PostgreSQL major version upgrades in a replication cluster setup. I was quite happy that it has been heard and some other people in different communities giving talks at meetups and other conferences about near-zero downtime upgrades using logical replication. Given that there is a talk that I gave at PGDAY'17 Russia, PGConf.EU 2017 in Warsaw and lastly at FOSDEM PGDay 2018 in Brussels, I thought it is better to create a blog post to keep this presentation available to the folks who could not make it to any of the conferences aforementioned. If you would like to directly go the talk and skip reading this blog post here is your link: Near-Zero Downtime (more…)
During the Postgres Open 2017 conference in San Francisco, someone came to the 2ndQuadrant booth and struck up a conversation with me. During our shameless geeking out over database mechanics, he asked me if pglogical supported the new Postgres 10 partitions. Given my noted expertise in all things Postgres, I answered in the appropriate manner:
"I have no idea. I'll have to look into that."
Well, after a bit of experimentation, I have a more concrete answer, and it's reassuringly positive.
Given a table on a provider node, is it possible to capture only INSERT traffic such that it accumulates on a subscribed system for archival purposes? It's a fairly common tactic, and allows an active OLTP system to regularly purge old data, while a reporting OLAP system keeps it (more…)
Logical replication uses a publish/subscribe model and so we create publications on the upstream (or publisher) and subscriptions on downstream (or subscriber). For more details about it, please refer to this blog post from my colleague Petr Jelinek, and also to the PostgreSQL documentation.
Here we will show how to build a test environment to play with this new feature from PostgreSQL 10, and how to configure it using OmniDB 2.1.
2. Building test environment
Let's build a 2-node test environment to illustrate how to configure PG10 logical replication feature within OmniDB.
2.1. Pull OmniDB repo
The first thing you need to do is to download OmniDB in the repo from GitHub and make sure you are in the development branch. Run the following:
2.2. Create 2 virtual (more…)
PostgreSQL 10 is getting close to its first beta release and it will include the initial support for logical replication, which is was written primarily by me and committed by my colleague Peter Eisentraut, and is internally based on the work 2ndQuadrant did on pglogical (even though the user interface is somewhat different).
I'd like to share some overview of basics in this blog post.
What's logical replication?
Let me start with briefly mentioning what logical replication is and what's it good for. I expect that most people know the PostgreSQL streaming master-standby replication that has been part of PostgreSQL for years and is commonly used both for high availability and read scaling.
So why add another replication mechanism and why call it logical? Well, the traditional (more…)
A few weeks ago I explained basics of autovacuum tuning. At the end of that post I promised to look into problems with vacuuming soon. Well, it took a bit longer than I planned, but here we go.
To quickly recap, autovacuum is a background process cleaning up dead rows, e.g. old deleted row versions. You can also perform the cleanup manually by running VACUUM, but autovacuum does that automatically depending on the amount of dead rows in the table, at the right moment - not too often but frequently enough to keep the amount of "garbage" under control.
PostgreSQL 9.6 is now out and so is an updated version of pglogical that works with it.
For quick guide on how to upgrade the database with pglogical you can check my post which announced 9.6beta support.
The main change besides the support for 9.6.x release of PostgreSQL is in the way we handle the output plugin and apply plugin. They have now been merged into single code base and single package so that there is no need to track the pglogical_output separately for the users and developers alike.
We fixed several bugs this time and also made upgrades from 9.4 much easier.
Here is a more detailed list of changes:
keepalive is tuned to much smaller values by default so that pglogical will notice network issues earlier
better compatibility when upgrading from PostgreSQL 9.4 (more…)
BDR is both a patch to PostgreSQL core and an extension on top of PostgreSQL core. How did that come about, and what's it's future?
Development of BDR was initiated around the time PostgreSQL 9.2 was in development. Arguably earlier if you count things like the extension mechanism. The goal of BDR is, and has always been, to add necessary features to core PostgreSQL to perform asynchronous loosely-coupled multi-master logical replication.
BDR improvements to core PostgreSQL
Since it's such a large set of changes it was necessary to structure development as a series of discrete features. A natural dividing line was "things that require changes to the core PostgreSQL code" vs "things that can be done in an extension". So the code was structured accordingly, making BDR a set of patches (more…)
I'm pleased to say that Postgres-BDR is on its way to PostgreSQL 9.6, and even better, it works without a patched PostgreSQL.
BDR has always been an extension, but on 9.4 it required a heavily patched PostgreSQL, one that isn't fully on-disk-format compatible with stock community PostgreSQL 9.4. The goal all along has been to allow it to run as an extension on an unmodified PostgreSQL ... and now we're there.
The years of effort we at 2ndQuadrant have put into getting the series of patches from BDR into PostgreSQL core have paid off. As of PostgreSQL 9.6, the only major patch that Postgres-BDR on 9.4 has that PostgreSQL core doesn't, is the sequence access method patch that powers global sequences.
This means that Postgres-BDR on 9.6 will not support global sequences, at least not (more…)