[task manager] do not sort tasks to be claimed by score if no pinned …

…tasks (#80692) (#81495)

resolves: #80371

Previously, when claiming tasks, we were always sorting the tasks to claim by
the score and then by the time they should be run.  We sort by score to
capture `runNow()` tasks, also referred to internally as "pinned" tasks
in the update by query.

The change in this PR is to only sort by score if there are pinned tasks, and
to not sort by score at all if there aren't any.

x-pack/plugins/task_manager/server/task_store.test.ts

@@ -367,7 +367,7 @@ describe('TaskStore', () => {
 
       const {
         args: {
-          updateByQuery: { body: { query } = {} },
+          updateByQuery: { body: { query, sort } = {} },
         },
       } = await testClaimAvailableTasks({
         opts: {
@@ -476,6 +476,25 @@ describe('TaskStore', () => {
           ],
         },
       });
+      expect(sort).toMatchObject([
+        {
+          _script: {
+            type: 'number',
+            order: 'asc',
+            script: {
+              lang: 'painless',
+              source: `
+if (doc['task.retryAt'].size()!=0) {
+  return doc['task.retryAt'].value.toInstant().toEpochMilli();
+}
+if (doc['task.runAt'].size()!=0) {
+  return doc['task.runAt'].value.toInstant().toEpochMilli();
+}
+    `,
+            },
+          },
+        },
+      ]);
     });
 
     test('it supports claiming specific tasks by id', async () => {

x-pack/plugins/task_manager/server/task_store.ts

@@ -46,6 +46,7 @@ import {
   RangeFilter,
   asPinnedQuery,
   matchesClauses,
+  SortOptions,
 } from './queries/query_clauses';
 
 import {
@@ -272,6 +273,17 @@ export class TaskStore {
       )
     );
 
+    // The documents should be sorted by runAt/retryAt, unless there are pinned
+    // tasks being queried, in which case we want to sort by score first, and then
+    // the runAt/retryAt.  That way we'll get the pinned tasks first.  Note that
+    // the score seems to favor newer documents rather than older documents, so
+    // if there are not pinned tasks being queried, we do NOT want to sort by score
+    // at all, just by runAt/retryAt.
+    const sort: SortOptions = [SortByRunAtAndRetryAt];
+    if (claimTasksById && claimTasksById.length) {
+      sort.unshift('_score');
+    }
+
     const apmTrans = apm.startTransaction(`taskManager markAvailableTasksAsClaimed`, 'taskManager');
     const { updated } = await this.updateByQuery(
       asUpdateByQuery({
@@ -288,12 +300,7 @@ export class TaskStore {
           status: 'claiming',
           retryAt: claimOwnershipUntil,
         }),
-        sort: [
-          // sort by score first, so the "pinned" Tasks are first
-          '_score',
-          // the nsort by other fields
-          SortByRunAtAndRetryAt,
-        ],
+        sort,
       }),
       {
         max_docs: size,