Improve the "findAssignmentsQuery":

- Fix an issue, where assignments, having an above-zero attempt_count, were finding their way to the results, just because they were prioritized based on their boost_level or pub_year. Apart from retrying the old failed assignments sooner, the non-yet-processed boosted-publications were pushed out to the workers much slower.
- Simplify the query, by removing the internal "ordering" and "limit", which had performance benefits when we did not need additional ordering for "level" and "pub_year". Back then, we wanted to apply the final orderings to as few rows as possible.

src/main/java/eu/openaire/urls_controller/services/UrlsServiceImpl.java

@@ -111,8 +111,7 @@ public class UrlsServiceImpl implements UrlsService {
         // Create the Assignments from the id-urls stored in the database up to the < assignmentsLimit >.
         String findAssignmentsQuery =
             "select pubid, url, datasourceid, datasourcename\n" +   // Select the final sorted data with "assignmentsLimit".
-            "from (select distinct pubid, url, datasourceid, datasourcename, level, pub_year, attempt_count\n" +  // Select the distinct id-url data. Beware that this will return duplicate id-url paris, wince one pair may be associated with multiple datasources.
-            "   from (select p.id as pubid, pu.url as url, pb.level as level, attempts.counts as attempt_count, p.year as pub_year, d.id as datasourceid, d.name as datasourcename\n" +  // Select all needed columns frm JOINs, order by "boost.level" and limit them to  (assignmentsLimit * 10)
+            "from (select distinct p.id as pubid, pu.url as url, pb.level as level, attempts.counts as attempt_count, p.year as pub_year, d.id as datasourceid, d.name as datasourcename\n" +   // Select the distinct id-url data. Beware that this will return duplicate id-url pairs, wince one pair may be associated with multiple datasources.
             "   from " + DatabaseConnector.databaseName + ".publication p\n" +
             "       join " + DatabaseConnector.databaseName + ".publication_urls pu on pu.id=p.id\n" +
             "       join " + DatabaseConnector.databaseName + ".datasource d on d.id=p.datasourceid\n" +  // This is needed for the "d.allow_harvest=true" check later on.
@@ -133,12 +132,9 @@ public class UrlsServiceImpl implements UrlsService {
             "       and not exists (select 1 from " + DatabaseConnector.databaseName + ".attempt a where a.id=p.id and a.error_class = 'noRetry' limit 1)\n" +
             "       and pu.url != '' and pu.url is not null\n" +   // Some IDs have empty-string urls, there are no "null" urls, but keep the relevant check for future-proofing.
             "       and (p.year <= " + currentYear + " or p.year > " + (currentYear + 5) + ")\n" +  // Exclude the pubs which will be published in the next 5 years. They don't provide full-texts now. (We don't exclude all future pubs, since, some have invalid year, like "9999").
-            "       order by coalesce(level, 0) desc, coalesce(pub_year, 0) desc\n" +
-            "       limit " + (assignmentsLimit * 10) + "\n" +
-            "   ) as non_distinct_results\n" +
-            "   order by coalesce(level, 0) desc, coalesce(pub_year, 0) desc, coalesce(attempt_count, 0), reverse(pubid), url\n" +  // We also order by reverse "pubid" and "url", in order to get the exactly same records for consecutive runs, all things being equal.
-            "   limit " + assignmentsLimit + "\n" +
-            ") as findAssignmentsQuery";
+            ") as distinct_results\n" +
+            "order by coalesce(attempt_count, 0), coalesce(level, 0) desc, coalesce(pub_year, 0) desc, reverse(pubid), url\n" +  // We also order by reverse "pubid" and "url", in order to get the exactly same records for consecutive runs, all things being equal.
+            "limit " + assignmentsLimit;
 
         // The datasourceID and datasourceName are currently not used during the processing in the Worker. They may be used by the Worker, in the future to apply a datasource-specific aggregation plugin to take the full-texts quickly, instead of using the general crawling one.
         // However, the "datasourceid" is useful to be able to generate the fileNames for the S3, without needing to perform additional select queries (with JOINs) at that phase.