Checkpoints are an integral part of a PostgreSQL server. Table data is not modified during query execution until modified rows, index pages, and other structures are committed to the Write Ahead Log (WAL). WAL files are also known as checkpoint segments. When the cumulative size of these files exceeds max_wal_size-or the time since the last checkpoint exceeds checkpoint_timeout-the data files are modified to reflect the changes.
This decoupled writing ensures database ...