Use line buffering for the input and output ports

As these are used for logging, which is done on a line by line basis. Remove
the now redundant calls to (force-output).

guix-data-service/jobs/load-new-guix-revision.scm

@@ -33,13 +33,11 @@
 
 (define (log-time action f)
   (simple-format #t "debug: Starting ~A\n" action)
-  (force-output)
   (let* ((start-time (current-time))
          (result (f))
          (time-taken (- (current-time) start-time)))
     (simple-format #t "debug: Finished ~A, took ~A seconds\n"
                    action time-taken)
-    (force-output)
     result))
 
 (define (all-inferior-package-derivations store inf packages)
@@ -124,7 +122,6 @@
                        (package-name package)
                        key
                        args)
-                      (force-output)
                       (exit 1))
                     (begin
                       (simple-format
@@ -133,7 +130,6 @@
                        (package-name package)
                        key
                        args)
-                      (force-output)
                       '()))))))
         (list ,@(map inferior-package-id packages)))))
 
@@ -425,7 +421,6 @@
                          "Failed extracting information from commit: ~A\n\n" commit)
           (simple-format (current-error-port)
                          "  ~A ~A\n\n" key args)
-          (force-output)
           #f)))))
 
 (define (store-item-for-git-repository-id-and-commit

guix-data-service/model/derivation.scm

@@ -362,7 +362,6 @@ ORDER BY derivations.system DESC,
       (simple-format
        #t "debug: ensure-input-derivations-exist: processing ~A derivations\n"
        (length input-derivation-file-names))
-      (force-output)
       (let* ((existing-derivation-entries
               (derivation-file-names->vhash conn
                                             derivation-ids-hash-table
@@ -443,7 +442,6 @@ ORDER BY derivations.system DESC,
 
     (simple-format
      #t "debug: insert-missing-derivations: ensure-input-derivations-exist\n")
-    (force-output)
 
     (ensure-input-derivations-exist (deduplicate-strings
                                      (map derivation-input-path

scripts/guix-data-service-process-jobs.in

@@ -27,6 +27,9 @@
              (guix-data-service database)
              (guix-data-service jobs))
 
+(setvbuf (current-output-port) 'line)
+(setvbuf (current-error-port) 'line)
+
 (with-postgresql-connection
  (lambda (conn)
    (simple-format #t "Ready to process jobs...\n")

scripts/guix-data-service.in

@@ -80,6 +80,9 @@
      (error "extraneous argument" arg))
    %default-options))
 
+(setvbuf (current-output-port) 'line)
+(setvbuf (current-error-port) 'line)
+
 (let ((opts (parse-options (cdr (program-arguments)))))
   (let ((repl-port (assoc-ref opts 'listen-repl)))
     (when repl-port