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.
In versions older than PostgreSQL 9.5, checkpoints were specified as a count of 16 MB files with the checkpoint_segments parameter, rather than a cumulative total size. The setting for max_wal_size in MB is roughly equivalent to checkpoint_segments * 16.
This decoupled writing approach ensures database integrity, at the cost of doubling the necessary disk writes. This is the main reason why some experienced PostgreSQL...
