Postgres High Availability Terms

 What is High Availability?

It is the amount of time that a service is available and is usually defined by the business.

Redundancy is the basis for high availability; in the event of an incident, we can continue to operate without problems.

 

Continuous Recovery

If and when an incident occurs, we have to restore a backup and then apply the wal logs; The recovery time would be very high and we would not be talking about high availability.

However, if we have the backups and the logs archived in a contingency server, we can apply the logs as they arrive.

If the logs are sent and applied every 1 minute, the contingency base would be in a continuous recovery and would have an outdated state to the production of at most 1 minute.

 

Standby Databases

The idea of a standby database is to keep a copy of a production database that always has the same data and that is ready to be used in case of an incident.

 

There are several ways to classify a standby database:

By the nature of the replication:

• Physical standbys: Disk blocks are copied.
• Logical standbys: Streaming of the data changes.
• Read more: All about Physical Replication and Log shipping in Postgres  

 

By the synchronicity of the transactions:

• Asynchronous: There is the possibility of data loss.
• Synchronous: There is no possibility of data loss; The commits in the master wait for the response of the standby.
• Read more: Configure Streaming Replication in PostgreSQL and Streaming-Replication Sync and Async, benefits of streaming replication over Log-shipping

 

By the usage:

• Warm standbys: They do not support connections.
• Hot standbys: Support read-only connections.

 

A cluster is a group of hosts working together and seen as one.

This provides a way to achieve horizontal salability and the ability to process more work by adding servers.

It can resist the failure of a node and continue to work transparently.

There are two models depending on what is shared:

Shared-storage: All nodes access the same storage with the same information.

Shared-nothing: Each node has its own storage, which may or may not have the same information as the other nodes, depending on the structure of our system.

Hope you got some idea on  High Availability . See you all soon with another good blog.... :)

Do post your comments or suggestions, which are greatly appreciated.

-- Nikhil

Found this post interesting? Subscribe us  😊😉

Read more 

Configure Streaming Replication in PostgreSQL

All about Physical Replication and Log shipping in Postgres 

Streaming-Replication Sync and Async, benefits of streaming replication over Log-shipping