Improve the metric handling further

This should avoid the metric being adjusted before it's been set
initially.

1 files changed, 57 insertions, 53 deletions

diff --git a/nar-herder/storage.scm b/nar-herder/storage.scm
index b78d4ed..6a6d630 100644
--- a/nar-herder/storage.scm
+++ b/nar-herder/storage.scm
@@ -59,13 +59,6 @@
 (define* (remove-nar-files-by-hash database storage-root metrics-registry
                                    hash
                                    #:key (error-unless-files-to-remove? #t))
-  (define nar-files-metric
-    (or (metrics-registry-fetch-metric metrics-registry
-                                       "nar_files_total")
-        (make-gauge-metric metrics-registry
-                           "nar_files_total"
-                           #:labels '(stored))))
-
   (let ((narinfo-files (database-select-narinfo-files database hash)))
     (when (and (null? narinfo-files)
                error-unless-files-to-remove?)
@@ -82,9 +75,14 @@
            (remove-nar-from-storage storage-root
                                     (assq-ref file 'url)))
 
-         (metric-decrement nar-files-metric
-                           #:label-values
-                           `((stored . ,(if exists? "true" "false"))))))
+         (and=> (metrics-registry-fetch-metric metrics-registry
+                                               "nar_files_total")
+                (lambda (metric)
+                  ;; Just update this metric if it exists, since if it
+                  ;; does, it should be set to a value
+                  (metric-decrement
+                   metric
+                   #:label-values `((stored . ,(if exists? "true" "false"))))))))
      narinfo-files)))
 
 (define (get-storage-size storage-root)
@@ -201,42 +199,49 @@
 (define* (update-nar-files-metric metrics-registry
                                   nar-file-counts
                                   #:key fetched-count removed-count)
-  (define nar-files-metric
-    (or (metrics-registry-fetch-metric metrics-registry
-                                       "nar_files_total")
-        (make-gauge-metric metrics-registry
-                           "nar_files_total"
-                           #:labels '(stored))))
-
-  ;; Set the values if the counts are known
-  (and=>
-   (assq-ref nar-file-counts 'stored)
-   (lambda (stored-count)
-     (metric-set nar-files-metric
-                 stored-count
-                 #:label-values '((stored . "true")))))
-  (and=>
-   (assq-ref nar-file-counts 'not-stored)
-   (lambda (not-stored-count)
-     (metric-set nar-files-metric
-                 not-stored-count
-                 #:label-values '((stored . "false")))))
-
-  ;; Then adjust by the fetched or removed counts
-  (when fetched-count
-    (metric-increment nar-files-metric
-                      #:by fetched-count
-                      #:label-values '((stored . "true")))
-    (metric-decrement nar-files-metric
-                      #:by fetched-count
-                      #:label-values '((stored . "false"))))
-  (when removed-count
-    (metric-decrement nar-files-metric
-                      #:by removed-count
-                      #:label-values '((stored . "true")))
-    (metric-increment nar-files-metric
-                      #:by removed-count
-                      #:label-values '((stored . "false")))))
+
+  ;; Avoid incrementing or decrementing the metric if it hasn't been
+  ;; set yet
+  (when (or (metrics-registry-fetch-metric metrics-registry
+                                           "nar_files_total")
+            (= (length nar-file-counts) 2))
+
+    (let ((nar-files-metric
+           (or (metrics-registry-fetch-metric metrics-registry
+                                              "nar_files_total")
+               (make-gauge-metric metrics-registry
+                                  "nar_files_total"
+                                  #:labels '(stored)))))
+
+      ;; Set the values if the counts are known
+      (and=>
+       (assq-ref nar-file-counts 'stored)
+       (lambda (stored-count)
+         (metric-set nar-files-metric
+                     stored-count
+                     #:label-values '((stored . "true")))))
+      (and=>
+       (assq-ref nar-file-counts 'not-stored)
+       (lambda (not-stored-count)
+         (metric-set nar-files-metric
+                     not-stored-count
+                     #:label-values '((stored . "false")))))
+
+      ;; Then adjust by the fetched or removed counts
+      (when fetched-count
+        (metric-increment nar-files-metric
+                          #:by fetched-count
+                          #:label-values '((stored . "true")))
+        (metric-decrement nar-files-metric
+                          #:by fetched-count
+                          #:label-values '((stored . "false"))))
+      (when removed-count
+        (metric-decrement nar-files-metric
+                          #:by removed-count
+                          #:label-values '((stored . "true")))
+        (metric-increment nar-files-metric
+                          #:by removed-count
+                          #:label-values '((stored . "false")))))))
 
 (define (check-storage database storage-root metrics-registry)
   (define files-count
@@ -546,7 +551,6 @@ When VERIFY-CERTIFICATE? is true, verify HTTPS server certificates."
   (define (download-nars initial-storage-size)
     ;; If there's free space, then consider downloading missing nars
     (if (< initial-storage-size storage-limit)
-
         (let ((result
                nar-file-counts
                (fold-nar-files
@@ -595,8 +599,8 @@ When VERIFY-CERTIFICATE? is true, verify HTTPS server certificates."
              (update-nar-files-metric metrics-registry
                                       nar-file-counts
                                       #:fetched-count fetched-count)
-             (> fetched-count 0))))
-        #f))
+             fetched-count)))
+        0))
 
   (define (fast-download-nars)
     (define parallelism 3)
@@ -654,7 +658,8 @@ When VERIFY-CERTIFICATE? is true, verify HTTPS server certificates."
 
           (update-nar-files-metric metrics-registry
                                    nar-file-counts
-                                   #:fetched-count fetched-count)))))
+                                   #:fetched-count fetched-count)
+          fetched-count))))
 
   (define (run-mirror-pass)
     (log-msg 'DEBUG "running mirror pass")
@@ -662,12 +667,11 @@ When VERIFY-CERTIFICATE? is true, verify HTTPS server certificates."
                                   (get-storage-size storage-root))))
       (metric-set storage-size-metric
                   initial-storage-size)
-      (let ((any-change?
+      (let ((fetched-count
              (if no-storage-limit?
                  (fast-download-nars)
                  (download-nars initial-storage-size))))
-        (log-msg 'DEBUG "finished mirror pass (any change? " any-change? ")")
-        any-change?)))
+        (log-msg 'DEBUG "finished mirror pass (fetched " fetched-count " nars)"))))
 
   (let ((channel (make-channel)))
     (spawn-fiber