High Availability and Replication

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me>
wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

David J.

What David said 😉

Disclaimer – I work for Quest Software – we produce database tools, including SharePlex, which can be used to help create High Availably and Disaster Recovery solutions.

Here’s a blog I did several years ago that might be helpful
https://www.quest.com/community/blogs/b/database-management/posts/high-availability-vs-disaster-recovery---what-s-the-difference

Clay Jackson
Database Solutions Sales Engineer
[cid:image001.jpg@01DA6B01.DC2DA850]<https://www.quest.com/solutions/database-performance-monitoring/&gt;
clay.jackson@quest.com<mailto:clay.jackson@quest.com>
office 949-754-1203 mobile 425-802-9603

From: David G. Johnston <david.g.johnston@gmail.com>
Sent: Thursday, February 29, 2024 11:15 AM
To: normandavis1990 <normandavis1990@proton.me>
Cc: pgsql-general@lists.postgresql.org
Subject: Re: High Availability and Replication

CAUTION: This email originated from outside of the organization. Do not follow guidance, click links, or open attachments unless you recognize the sender and know the content is safe.

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me<mailto:normandavis1990@proton.me>> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

David J.

What does this technique do?

On Thursday, February 29th, 2024 at 10:45 PM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On 2/29/24 12:02, normandavis1990 wrote:

What does this technique do?

https://www.postgresql.org/docs/current/high-availability.html

On Thursday, February 29th, 2024 at 10:45 PM, David G. Johnston
<david.g.johnston@gmail.com> wrote:

On Thursday, February 29, 2024, normandavis1990
<normandavis1990@proton.me <mailto:normandavis1990@proton.me>> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

David J.

--
Adrian Klaver
adrian.klaver@aklaver.com

On Feb 29, 2024, at 10:15 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me <mailto:normandavis1990@proton.me>> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

Perhaps more specifically: Replication is simply Replicating - or copying - the “master” database to one or more “slave” databases, generally in real-time such that the slave database clusters are replicas of the master. This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.

High Availability layers on top of replication to provide some means of ensuring that the database is HIGHLY available, such as an automatic failover system or load balancer. Many different options that work in many different ways are available to help meet this goal.
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

On Thursday, February 29th, 2024 at 11:38 PM, Israel Brewster <ijbrewster@alaska.edu> wrote:

On Feb 29, 2024, at 10:15 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

Perhaps more specifically: Replication is simply Replicating - or copying - the “master” database to one or more “slave” databases, generally in real-time such that the slave database clusters are replicas of the master. This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.

High Availability layers on top of replication to provide some means of ensuring that the database is HIGHLY available, such as an automatic failover system or load balancer. Many different options that work in many different ways are available to help meet this goal.
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

David J.

Hi,
You said "This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.". What does "goes down" mean?
In Replication mode, if the primary server is shut down, then the data will also be lost?

On Mar 1, 2024, at 11:36 AM, normandavis1990 <normandavis1990@proton.me> wrote:

On Thursday, February 29th, 2024 at 11:38 PM, Israel Brewster <ijbrewster@alaska.edu> wrote:

On Feb 29, 2024, at 10:15 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me <mailto:normandavis1990@proton.me>> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

Perhaps more specifically: Replication is simply Replicating - or copying - the “master” database to one or more “slave” databases, generally in real-time such that the slave database clusters are replicas of the master. This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.

High Availability layers on top of replication to provide some means of ensuring that the database is HIGHLY available, such as an automatic failover system or load balancer. Many different options that work in many different ways are available to help meet this goal.
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

David J.

Hi,
You said "This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.". What does "goes down" mean?

Exactly what I said - it goes down. Not functioning. Offline. Inaccessible. It is not up and running, therefore, it is down.

In Replication mode, if the primary server is shut down, then the data will also be lost?

No. As I said - and you quoted - “When the master goes down…you’ll still have one or more copies of it available”. So no, the data will NOT be lost.

---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

Hi,

When Master server goes down, either you need to promote one of slave node
or configure HA mechanism so that in case of master server goes down it
will automatically promote the slave server as new master.

Patroni HA tool would be good option for your requirement.

https://patroni.readthedocs.io/en/latest/README.html

Hope this helps.

Thanks & Regards,
Abdul Sayeed
PostgreSQL DBA

On Sat, 2 Mar 2024 at 2:15 AM, Israel Brewster <ijbrewster@alaska.edu>
wrote:

On Saturday, March 2nd, 2024 at 12:14 AM, Israel Brewster <ijbrewster@alaska.edu> wrote:

On Mar 1, 2024, at 11:36 AM, normandavis1990 <normandavis1990@proton.me> wrote:

On Thursday, February 29th, 2024 at 11:38 PM, Israel Brewster <ijbrewster@alaska.edu> wrote:

On Feb 29, 2024, at 10:15 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

Perhaps more specifically: Replication is simply Replicating - or copying - the “master” database to one or more “slave” databases, generally in real-time such that the slave database clusters are replicas of the master. This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.

High Availability layers on top of replication to provide some means of ensuring that the database is HIGHLY available, such as an automatic failover system or load balancer. Many different options that work in many different ways are available to help meet this goal.
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

David J.

Hi,
You said "This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.". What does "goes down" mean?

Exactly what I said - it goes down. Not functioning. Offline. Inaccessible. It is not up and running, therefore, it is down.

In Replication mode, if the primary server is shut down, then the data will also be lost?

No. As I said - and you quoted - “When the master goes down…you’ll still have one or more copies of it available”. So no, the data will NOT be lost.

---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

Hi,
Therefore, in both HA and Replication, when the primary server is shut down, the information is not lost, and the only difference is that in the HA mechanism, another server replaces the primary one, but this is not the case in Replication. Is it true?

On Saturday, March 2nd, 2024 at 1:24 AM, Abdul Sayeed <abdulsayeed24@gmail.com> wrote:

Hi,

When Master server goes down, either you need to promote one of slave node or configure HA mechanism so that in case of master server goes down it will automatically promote the slave server as new master.

Patroni HA tool would be good option for your requirement.

https://patroni.readthedocs.io/en/latest/README.html

Hope this helps.

Thanks & Regards,
Abdul Sayeed
PostgreSQL DBA

On Sat, 2 Mar 2024 at 2:15 AM, Israel Brewster <ijbrewster@alaska.edu> wrote:

On Mar 1, 2024, at 11:36 AM, normandavis1990 <normandavis1990@proton.me> wrote:

On Thursday, February 29th, 2024 at 11:38 PM, Israel Brewster <ijbrewster@alaska.edu> wrote:

On Feb 29, 2024, at 10:15 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Thursday, February 29, 2024, normandavis1990 <normandavis1990@proton.me> wrote:

What is the difference between High Availability and Replication?

The former is a goal, the later is a technique.

Perhaps more specifically: Replication is simply Replicating - or copying - the “master” database to one or more “slave” databases, generally in real-time such that the slave database clusters are replicas of the master. This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.

High Availability layers on top of replication to provide some means of ensuring that the database is HIGHLY available, such as an automatic failover system or load balancer. Many different options that work in many different ways are available to help meet this goal.
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
[2156 Koyukuk Drive](https://www.google.com/maps/search/2156+Koyukuk+Drive+Fairbanks+AK+99775-7320?entry=gmail)
[Fairbanks AK 99775-7320](https://www.google.com/maps/search/2156+Koyukuk+Drive+Fairbanks+AK+99775-7320?entry=gmail)
Work: 907-474-5172
cell: 907-328-9145

David J.

Hi,
You said "This is good when the master goes down, because you’ll still have one or more copies of it available, but by itself it doesn’t keep there from being an outage if/when the master goes down.". What does "goes down" mean?

Exactly what I said - it goes down. Not functioning. Offline. Inaccessible. It is not up and running, therefore, it is down.

In Replication mode, if the primary server is shut down, then the data will also be lost?

No. As I said - and you quoted - “When the master goes down…you’ll still have one or more copies of it available”. So no, the data will NOT be lost.

---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
[2156 Koyukuk Drive](https://www.google.com/maps/search/2156+Koyukuk+Drive+Fairbanks+AK+99775-7320?entry=gmail)
[Fairbanks AK 99775-7320](https://www.google.com/maps/search/2156+Koyukuk+Drive+Fairbanks+AK+99775-7320?entry=gmail)
Work: 907-474-5172
cell: 907-328-9145

Hi,
Does installing Patroni cause the primary server to stop even for a short time?

Hi,

Not required.

Thanks & Regards,
Abdul Sayeed
PostgreSQL DBA
Postgres Professional Certified
Skype: abdul.sayeed24

On Sat, 2 Mar 2024 at 12:21 PM, normandavis1990 <normandavis1990@proton.me>
wrote: