Prioritize tasks that have never run at all

src/database-backends/postgresql/queries/get-task-stream.js

@@ -60,29 +60,34 @@ function makeFillQuery(withDependencies) {
 						SELECT item_id FROM tag_candidates
 					`
 				}
+			),
+			tasks AS NOT MATERIALIZED (
+				SELECT
+					item_id,
+					is_successful,
+					(
+						results.is_successful = FALSE
+						OR (
+							results.is_successful = TRUE
+							AND results.is_invalidated = FALSE
+							AND (
+								results.expires_at > NOW()
+								OR results.expires_at IS NULL
+							)
+						)
+					) AS is_completed
+				FROM srap_task_results AS results
+				WHERE
+					results.task = :task
+					AND results.task_version = :taskVersion
 			)
 		SELECT
 			:task AS task,
-			item_id
+			full_candidates.item_id
 		FROM full_candidates
-		WHERE NOT EXISTS (
-			SELECT item_id FROM srap_task_results AS results
-			WHERE
-				item_id = full_candidates.item_id
-				AND results.task = :task
-				AND results.task_version = :taskVersion
-				AND (
-					results.is_successful = FALSE
-					OR (
-						results.is_successful = TRUE
-						AND results.is_invalidated = FALSE
-						AND (
-							results.expires_at > NOW()
-							OR results.expires_at IS NULL
-						)
-					)
-				)
-		)
+		LEFT JOIN tasks ON full_candidates.item_id = tasks.item_id
+		WHERE tasks.is_completed IS NOT TRUE
+		ORDER BY tasks.is_successful NULLS FIRST
 	`;
 }