Type: integer
Default: 80 (80MB)
Min: 2 (2MB)
Max: 2147483647 (2147483647MB)
Unit: MB
Context: sighup
Restart: false
Since: 9.5

As long as WAL disk usage stays below this setting, old WAL files are always recycled for future use at a checkpoint, rather than removed. This can be used to ensure that enough WAL space is reserved to handle spikes in WAL usage, for example when running large batch jobs. If this value is specified without units, it is taken as megabytes. The default is 80 MB. This parameter can only be set in the postgresql.conf file or on the server command line.