Move logging cleanup tasks to after the transaction commits

As I think some operations (like the database backup) can block the DROP
SEQUENCE bit, so at least this approach means that the main transaction should
commit and then the sequence is eventually dropped.

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

@@ -303,7 +303,7 @@ WHERE job_id = $1")
   (exec-query
    conn
    (string-append
-    "DROP SEQUENCE "
+    "DROP SEQUENCE IF EXISTS "
     (log-part-sequence-name job-id))))
 
 (define (vacuum-log-parts-table conn)
@@ -1820,13 +1820,15 @@ SKIP LOCKED")
                  (close-port logging-port)
 
                  (combine-log-parts! logging-conn id)
-                 (drop-log-parts-sequence logging-conn id)
-                 (with-time-logging "vacuuming log parts"
-                   (vacuum-log-parts-table logging-conn))
 
                  result))))))
     result))
 
+(define (cleanup-logging id conn)
+  (drop-log-parts-sequence conn id)
+  (with-time-logging "vacuuming log parts"
+    (vacuum-log-parts-table conn)))
+
 (prevent-inlining-for-tests setup-logging)
 
 (define (process-load-new-guix-revision-job id)
@@ -1881,6 +1883,10 @@ SKIP LOCKED")
               (record-job-event conn id "success")
               (exec-query conn "COMMIT")
 
+              (with-time-logging
+                  "cleanup logging"
+                (cleanup-logging id conn))
+
               (with-time-logging
                   "vacuuming package derivations by guix revision range table"
                 (vacuum-package-derivations-table conn))
@@ -1889,6 +1895,11 @@ SKIP LOCKED")
             (begin
               (exec-query conn "ROLLBACK")
               (record-job-event conn id "failure")
+
+              (with-time-logging
+                  "cleanup logging"
+                (cleanup-logging id conn))
+
               #f)))
        (()
         (exec-query conn "ROLLBACK")