High Availability and Scalable Reads in PostgreSQL

PostgreSQL, a popular database management system, supports scaling through streaming replication. This feature enables higher read performance and high availability (HA) by streaming records of database modifications from the primary server to one or more replicas. The Write Ahead Log (WAL) is used for this purpose, capturing every atomic database change and ensuring durability. PostgreSQL supports three basic modes of replication: asynchronous, synchronous write, and synchronous apply. Each mode offers different levels of consistency guarantees and impacts on write performance. Asynchronous replication is the most performant for inserts but can result in temporary data inconsistency between the primary and replicas. Synchronous write ensures that all specified replicas will write their data to the WAL, while synchronous apply guarantees not only that the WAL will be written to all specified replicas but also that the WAL segments will be fully applied to the database. In terms of read performance, using streaming replication with multiple nodes can lead to a significant increase in query speed. The benefits of scaling reads linearly as more replica nodes are added to the cluster. Users should carefully weigh their requirements and costs when choosing which replication mode to use for their specific workloads.