Upon creating a subscription, PostgreSQL will automatically sync any pre-existing data from the master to the replica.
In our case there is no data to sync since the widgets table is empty, but this is a useful feature when adding new subscriptions to an existing database. On db-master , insert the following data on the widgets table:.click here
Replication, Clustering, and Connection Pooling
The entries have been successfully replicated from db-master to db-replica. One thing to note about write queries on replica servers is that they are not replicated back to the master server. PostgreSQL currently has limited support for resolving conflicts when the data between servers diverges. If there is a conflict, the replication will stop and PostgreSQL will wait until the issue is manually fixed by the database administrator.
For that reason, most applications will direct all write operations to the master server, and distribute reads among available replica servers. After resolving the existing problem s , replication should take place automatically. You now have the required knowledge to experiment with horizontal read scaling, high availability, and the geographical distribution of your PostgreSQL database by adding additional replica servers.
What is WAL?
Redis comes with several commands that can help with troubleshooting and debugging issues. Because of its nature as an in-memory key-value store, many of these commands focus on memory management, but there are others that are valuable for providing an overview of the state of your Redis server. This tutorial will provide details on how to use some of these commands to help diagnose and resolve issues you may run into as you use Redis.
A Redis hash is a data type that represents a mapping between a string field and a string value. A single hash can hold many field-value pairs and are designed to not take up much space, making them ideal for representing data objects. This tutorial will go over how to manage hashes in Redis, from creating them to retrieving and deleting the data held within a hash. In Redis, a list is a collection of strings sorted by the order in which they were inserted unless otherwise specified, similar to linked lists.
This tutorial details how to create lists and retrieve and delete elements from lists. In Redis, strings are the most basic type of value you can create and manage. This tutorial provides an overview of how to create and retrieve strings, as well as how to manipulate the values held by string keys. Twitter Facebook Hacker News.
DigitalOcean home. Community Control Panel. Hacktoberfest Contribute to Open Source. View All Results. By coreh Become an author. Prerequisites To follow this tutorial, you will need: Two Ubuntu To set these up, follow this initial server setup tutorial.
Synchronous and asynchronous replication
Private networking enabled on your servers. Private networking allows for communication between your servers without the security risks associated with exposing databases to the public internet. Step 1 — Configuring PostgreSQL for Logical Replication There are several configuration settings you will need to modify to enable logical replication between your servers. By coreh.
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Related Cheatsheet How To Troubleshoot Issues in Redis Redis comes with several commands that can help with troubleshooting and debugging issues. How To Manage Hashes in Redis A Redis hash is a data type that represents a mapping between a string field and a string value. How To Manage Lists in Redis In Redis, a list is a collection of strings sorted by the order in which they were inserted unless otherwise specified, similar to linked lists. Still looking for an answer?
PostgreSQL: Documentation: High Availability, Load Balancing, and Replication
Ask a question Search for more help. Log in to the postgres user and start PostgreSQL shell:. So it will have only READ permissions. To sync from master to slave server, the PostgreSQL main directory on the slave must be replaced with the main directory from the master. In the slave server , log in to the postgres user:. Once the transfer is complete, in the main directory create a new recovery. This is just one of the many replication capabilities provided by this advanced and fully open source database system.
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