Associate a name with database connections

This helps when working out which connection to the database is doing what.

guix-data-service/database.scm

@@ -24,10 +24,12 @@
 (define pg-conn-finish
   (@@ (squee) pg-conn-finish))
 
-(define (with-postgresql-connection f)
+(define* (with-postgresql-connection name f)
   (define paramstring
-    (or (getenv "GUIX_DATA_SERVICE_DATABASE_PARAMSTRING")
-        "dbname=guix_data_service user=guix_data_service"))
+    (string-append
+     (or (getenv "GUIX_DATA_SERVICE_DATABASE_PARAMSTRING")
+         "dbname=guix_data_service user=guix_data_service")
+     " application_name='guix-data-service " name "'"))
 
   (let* ((conn (connect-to-postgres-paramstring paramstring)))
     (with-throw-handler

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

@@ -703,6 +703,7 @@ ORDER BY load_new_guix_revision_jobs.id DESC")
                      (lambda ()
                        (let ((result
                               (with-postgresql-connection
+                               (simple-format #f "load-new-guix-revision ~A logging" id)
                                (lambda (logging-conn)
                                  (insert-empty-log-entry logging-conn id)
                                  (let ((logging-port (log-port id logging-conn)))

guix-data-service/web/controller.scm

@@ -568,6 +568,7 @@
               #t
               (lambda ()
                 (with-postgresql-connection
+                 "web healthcheck"
                  (lambda (conn)
                    (number?
                     (string->number
@@ -585,6 +586,7 @@
                    500))))
     (_
      (with-postgresql-connection
+      "web"
       (lambda (conn)
         (controller-with-database-connection request
                                              method-and-path-components