Improving docs on this

docs/PostgreSQL.md

@@ -329,6 +329,11 @@ WAL-G will also prefetch WAL files ahead of asked WAL file. These files will be
 wal-g wal-fetch example-archive new-file-name
 ```
 
+Note: ``wal-fetch`` will exit with errorcode 74 (EX_IOERR: input/output error, see sysexits.h for more info) if the WAL-file is not available in the repository.
+All other errors end in exit code 1, and should stop PostgreSQL rather than ending PostgreSQL recovery.
+For PostgreSQL that should be any error code between 126 and 255, which can be achieved with a simple wrapper script.
+Please see https://github.com/wal-g/wal-g/pull/1195 for more information.
+
 ### ``wal-push``
 
 When uploading WAL archives to S3, the user should pass in the absolute path to where the archive is located.

internal/databases/postgres/wal_fetch_handler.go

@@ -17,6 +17,9 @@ import (
 	"github.com/wal-g/wal-g/utility"
 )
 
+// Looking at sysexits.h, EX_IOERR (74) is defined as a generic exit code for input/output errors
+const exIoError=74
+
 type InvalidWalFileMagicError struct {
 	error
 }
@@ -98,7 +101,7 @@ func HandleWALFetch(folder storage.Folder, walFileName string, location string,
 	err := internal.DownloadFileTo(folder, walFileName, location)
 	if _, isArchNonExistErr := err.(internal.ArchiveNonExistenceError); isArchNonExistErr {
 		tracelog.ErrorLogger.Print(err.Error())
-		os.Exit(74)
+		os.Exit(exIoError)
 	} else {
 		tracelog.ErrorLogger.FatalOnError(err)
 	}