From f2f9b154adb8055110df6e98718e283157494226 Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Mon, 15 Apr 2024 15:06:05 +0100
Subject: Make the number of database reader threads configurable

---
 nar-herder/database.scm |  8 +++-----
 nar-herder/server.scm   |  4 +++-
 scripts/nar-herder.in   | 14 ++++++++++++--
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/nar-herder/database.scm b/nar-herder/database.scm
index 2db561a..4fa145f 100644
--- a/nar-herder/database.scm
+++ b/nar-herder/database.scm
@@ -259,7 +259,8 @@ CREATE TABLE scheduled_cached_narinfo_removal (
    "CREATE INDEX IF NOT EXISTS narinfo_files_narinfo_id
       ON narinfo_files (narinfo_id);"))
 
-(define (setup-database database-file metrics-registry)
+(define* (setup-database database-file metrics-registry
+                         #:key (reader-threads 1))
   (define mmap-size #f)
 
   (let ((db (db-open database-file)))
@@ -302,10 +303,7 @@ CREATE TABLE scheduled_cached_narinfo_removal (
           #:name "db r"
 
           ;; Use a minimum of 2 and a maximum of 8 threads
-          #:parallelism
-          (min (max (current-processor-count)
-                    2)
-               64)
+          #:parallelism reader-threads
           #:delay-logger (let ((delay-metric
                                 (make-histogram-metric
                                  metrics-registry
diff --git a/nar-herder/server.scm b/nar-herder/server.scm
index dd59216..2b941b9 100644
--- a/nar-herder/server.scm
+++ b/nar-herder/server.scm
@@ -631,7 +631,9 @@
     (make-scheduler #:parallelism 1))
 
   (let* ((database (setup-database (assq-ref opts 'database)
-                                   metrics-registry))
+                                   metrics-registry
+                                   #:reader-threads
+                                   (assq-ref opts 'database-reader-threads)))
          (canonical-storage (and=> (assq-ref opts 'storage)
                                    canonicalize-path))
 
diff --git a/scripts/nar-herder.in b/scripts/nar-herder.in
index 459526e..67515dc 100644
--- a/scripts/nar-herder.in
+++ b/scripts/nar-herder.in
@@ -312,10 +312,16 @@
                 (lambda (opt name arg result)
                   (alist-cons 'parallelism
                               (string->number arg)
-                              (alist-delete 'parallelism result))))))
+                              (alist-delete 'parallelism result))))
+
+        (option '("database-reader-threads") #t #f
+                (lambda (opt name arg result)
+                  (alist-cons 'database-reader-threads
+                              (string->number arg)
+                              (alist-delete 'database-reader-threads result))))))
 
 (define %server-option-defaults
-  '((port                                 . 8080)
+  `((port                                 . 8080)
     (host                                 . "0.0.0.0")
 
     (storage-limit                        . "none")
@@ -325,6 +331,10 @@
 
     (recent-changes-limit                 . 32768)
 
+    (database-reader-threads              . ,(min (max (current-processor-count)
+                                                       2)
+                                                  64))
+
     (parallelism                          . 1)))
 
 (define %check-options
-- 
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