--- a/schema/gemma.sql	Wed Jan 23 16:25:43 2019 +0100
+++ b/schema/gemma.sql	Wed Jan 23 17:58:57 2019 +0100
@@ -633,12 +633,14 @@
 );
 
 CREATE TABLE waterway.imports (
-    id        int PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
-    state     waterway.import_state NOT NULL DEFAULT 'queued',
-    kind      varchar   NOT NULL,
-    enqueued  timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
-    due       timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
-    trys_left int,
+    id         int PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
+    state      waterway.import_state NOT NULL DEFAULT 'queued',
+    kind       varchar   NOT NULL,
+    enqueued   timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    due        timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    retry_wait interval
+        CHECK(retry_wait IS NULL OR retry_wait >= interval '0 microseconds'),
+    trys_left  int, -- if NULL and retry_wait NOT NUL, endless
     username  varchar   NOT NULL
         REFERENCES internal.user_profiles(username)
             ON DELETE CASCADE