WAL

https://www.postgresql.org/docs/current/wal-intro.html

Write ahead log what Postgres uses for logging changes on the primary database, replication to secondary databases. It logs changes to WAL before flushing to disk.

High volume of transactions => Lots of WAL logs.

Vacuum also generates WAL logs.

Replica < WAL offset > Primary

WAL offset is called LSN and how much replica fall behind.

Wait events from AWS RDS