pgstef’s blog

2024-09-25

pgBackRest dedicated backup host

As I mentioned in my last blog post, as your cluster grows with multiple standby servers and potentially automated failover (using tools like Patroni), it becomes more practical to set up a dedicated repository host, also known as a dedicated backup server. This backup server can then trigger backups and automatically select the appropriate node in case of failover, eliminating the need for manual intervention.

In this post, I’ll show you how easy it is to add a repository host to an existing cluster. I’ll also give you a sneak peek at a new feature expected to be included in the next pgBackRest release 😉

2024-09-23

pgBackRest backups from the standby server

Recently, we’ve received many questions about how to take backups from a standby server using pgBackRest. In this post, I’d like to clarify one of the most frequently asked questions and address a common misconception for new users.

First of all, it’s important to understand that taking a backup exclusively from the standby server is not currently possible. When you trigger a backup from the standby, pgBackRest creates a standby backup that is identical to a backup performed on the primary. It does this by starting/stopping the backup on the primary, copying only files that are replicated from the standby, then copying the remaining few files from the primary.

For this setup to work, both the primary and standby servers must share a common backup repository. This can be any supported repository type.

Let’s take an example, using an NFS mount point.

2024-05-20

In-memory disk for PostgreSQL temporary files

Recently, while debugging a performance issue of a CREATE INDEX operation, I was reminded that PostgreSQL might produce temporary files when executing a parallel query, including parallel index creation, because each worker process has its own memory and might need to use disk space for sorting or hash tables.

Thanks to Peter Geoghegan answering this pgsql-admin email thread.

So, in order to try to speed up that index creation, I thought it would be beneficial to move those temporary files directly into memory using a tmpfs and wanted to test that theory, writing this blog post :-)

2023-07-03

pgBackRest differential vs incremental backup

One of the most frequent questions I get is to actually explain the difference between differential and incremental backups in pgBackRest.

As everyone might easily imagine, an incremental backup will only copy the database files (to keep it simple) that have been modified since the last successful backup. If you have a full backup every Sunday, and then an incremental every other day, the backup from Wednesday will be based on the one from Tuesday. That also means that if the backup from Monday or Tuesday is broken/corrupted (for any reason), you might not be able to recover from your Wednesday backup.

Now, what is a differential backup then? It is an incremental backup but it will be based on the last successful full backup. So if you have a full backup every Sunday, and then a differential every other day, the backup from Wednesday will be based on the one from Sunday! It would then doesn’t matter if the other differential backups get broken/corrupted, but since you’ll always compare what has been modified since Sunday, the size of the differential backups will be bigger over time.

Let’s have a concrete example.

2023-05-26

pgBackRest SFTP support

SFTP support has been added in the 2.46 release on 22 May 2022.

In this demo setup, the SFTP host will be called sftp-srv and the PostgreSQL node pg-srv. Both nodes will be running on Rocky Linux 8.

If you’re familiar with Vagrant, here’s a simple Vagrantfile to initiate 3 virtual machines using those names:

# Vagrantfile
Vagrant.configure(2) do |config|
    config.vm.box = 'rockylinux/8'
    config.vm.provider 'libvirt' do |lv|
        lv.cpus = 1
        lv.memory = 1024
    end
    config.vm.synced_folder ".", "/vagrant", disabled: true

    nodes  = 'sftp-srv', 'pg-srv'
    nodes.each do |node|
        config.vm.define node do |conf|
            conf.vm.hostname = node
        end
    end
end

When using Vagrant boxes, it might be needed to enable the SSH password authentication to proceed with SSH key exchange:

$ sudo -i
root# sed -i 's/PasswordAuthentication no/PasswordAuthentication yes/g' /etc/ssh/sshd_config    
root# systemctl restart sshd.service
root# passwd

2022-09-20

pgBackRest 2.41 released

With pgBackRest 2.41 just released, a new feature called backup annotations is now available. Let’s see in this blog post what this is about.

2022-07-12

Patroni and pgBackRest combined

I see more and more questions about pgBackRest in a Patroni cluster on community channels. So, following yesterday’s post about Patroni on pure Raft, we’ll see in this post an example about how to setup pgBackRest in such cases.

To prepare this post, I followed most of the instructions given by Federico Campoli at PGDAY RUSSIA 2021 about Protecting your data with Patroni and pgbackrest. The video recording might even be found here.

2022-07-11

Patroni on pure Raft

Since September 2020 and its 2.0 release, Patroni is able to rely on the pysyncobj module in order to use python Raft implementation as DCS.

In this post, we will setup a demo cluster to illustrate that feature.

2022-04-15

pgBackRest multi-repositories tips and tricks

Since April 2021 and the 2.33 release, pgBackRest allows using multiple repositories at the same time. This brings a lot of benefits like, for example, redundancy and the ability to define various retention policies.

I had the chance to talk about this feature recently at pgDay Paris to highlight the impact of this new feature on the existing pgBackRest commands.

A detailed example can also be found in an EDB docs page I wrote last year when this feature was released.

In this post, we’ll see the most frequent questions I get (in conferences or on community channels) and some tips and tricks.

2022-02-23

pgBackRest preview - Bundle files in the repository during backup

A nice new feature has been added on 14 Feb 2022: Bundle files in the repository during backup. Details can be found in commits 34d6495 and efc09db.

This feature combines smaller files during backup to reduce the number of files written to the repository (enabled with --bundle). Files are batched up to --bundle-size and then compressed/encrypted individually and stored sequentially in the bundle. --bundle-limit limits which files can be added to bundles. Files larger than this size will be stored separately. On backup resume, the bundles are removed and any remaining file is eligible to be resumed.

IMPORTANT NOTE: this feature is still experimental and will not be released in pgBackRest 2.38.

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