guix: Avoid ‘fdatasync’ call for caches and regular files.

Fixes <https://issues.guix.gnu.org/77606>.

Calling ‘fdatasync’ for each and every narinfo file created by ‘guix
substitute’ proved to be too expensive on spinning HDDs and/or under
load (from 0.1s to 1.3s for the ‘fdatasync’ call alone).

* guix/git-authenticate.scm (cache-authenticated-commit): Pass #:sync? #f.
* guix/http-client.scm (http-fetch/cached): Likewise.
* guix/scripts/discover.scm (write-publish-file): Likewise.
* guix/scripts/style.scm (format-whole-file): Likewise.
* guix/substitutes.scm (cache-narinfo!): Likewise.

Reported-by: Christopher Baines <mail@cbaines.net>
Change-Id: I82297eae737bc5aae8a3f7604119e9f3d4b625bf

5 files changed, 13 insertions, 8 deletions

diff --git a/guix/git-authenticate.scm b/guix/git-authenticate.scm
index 37c69d0880..3cd1175c32 100644
--- a/guix/git-authenticate.scm
+++ b/guix/git-authenticate.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2019, 2020, 2021, 2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2019-2022, 2025 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -344,7 +344,8 @@ authenticated (only COMMIT-ID is written to cache, though)."
           (chmod port #o600)
           (display ";; List of previously-authenticated commits.\n\n"
                    port)
-          (pretty-print lst port))))))
+          (pretty-print lst port)))
+      #:sync? #f)))
 
 
 ;;;
diff --git a/guix/http-client.scm b/guix/http-client.scm
index 9138a627ac..4e0cc59e91 100644
--- a/guix/http-client.scm
+++ b/guix/http-client.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012-2018, 2020-2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012-2018, 2020-2022, 2025 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2012, 2015 Free Software Foundation, Inc.
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
@@ -346,7 +346,8 @@ Write information about redirects to LOG-PORT."
           (when cache-port
             (close-port cache-port))
           (with-atomic-file-output file
-            (cut write-cache port <>))
+            (cut write-cache port <>)
+            #:sync? #f)
           (close-port port)
           (open-input-file file))))
 
diff --git a/guix/scripts/discover.scm b/guix/scripts/discover.scm
index 32bf6085a5..cbe01638f5 100644
--- a/guix/scripts/discover.scm
+++ b/guix/scripts/discover.scm
@@ -87,7 +87,8 @@ lock on FILE to synchronize with any potential readers."
          (format port "http://~a:~a~%"
                  (avahi-service-address service)
                  (avahi-service-port service)))
-       %publish-services)))
+       %publish-services))
+    #:sync? #f)
   (chmod file #o644))
 
 (define* (read-substitute-urls #:key (file (%publish-file)))
diff --git a/guix/scripts/style.scm b/guix/scripts/style.scm
index 4801529f7e..c45bdd4458 100644
--- a/guix/scripts/style.scm
+++ b/guix/scripts/style.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2021-2024 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2021-2025 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2024 Herman Rimm <herman@rimm.ee>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -554,7 +554,8 @@ are put in alphabetical order."
           (apply pretty-print-with-comments/splice port lst
                  #:format-comment canonicalize-comment
                  #:format-vertical-space canonicalize-vertical-space
-                 rest))))))
+                 rest))
+        #:sync? #f))))
 
 
 ;;;
diff --git a/guix/substitutes.scm b/guix/substitutes.scm
index 9edce5b2f8..24b7873ce2 100644
--- a/guix/substitutes.scm
+++ b/guix/substitutes.scm
@@ -127,7 +127,8 @@ indicates that PATH is unavailable at CACHE-URL."
     (mkdir-p (dirname file))
     (with-atomic-file-output file
       (lambda (out)
-        (write (cache-entry cache-url narinfo) out))))
+        (write (cache-entry cache-url narinfo) out))
+      #:sync? #f))
 
   narinfo)