Fix next-job query to do round-robin through job groups

modules/store/src/main/scala/docspell/store/queries/QJob.scala

@@ -60,8 +60,11 @@ object QJob {
       store.transact(for {
         n <- RJob.setScheduled(job.id, worker)
         _ <-
-          if (n == 1) RJobGroupUse.setGroup(RJobGroupUse(worker, job.group))
+          if (n == 1) RJobGroupUse.setGroup(RJobGroupUse(job.group, worker))
           else 0.pure[ConnectionIO]
+        _ <- logger.fdebug[ConnectionIO](
+          s"Scheduled job ${job.info} to worker ${worker.id}"
+        )
       } yield if (n == 1) Right(job) else Left(()))
 
     for {
@@ -98,22 +101,42 @@ object QJob {
     val stateCond =
       JC.state === JobState.waiting || (JC.state === JobState.stuck && stuckTrigger < now.toMillis)
 
+    object AllGroups extends TableDef {
+      val tableName = "allgroups"
+      val alias     = Some("ag")
+
+      val group: Column[Ident] = JC.group.copy(table = this)
+
+      val selectAll = Select(JC.group.s, from(JC), stateCond).distinct
+    }
+
     val sql1 =
       Select(
-        max(JC.group).as("g"),
-        from(JC).innerJoin(G, JC.group === G.group),
-        G.worker === worker && stateCond
+        select(min(AllGroups.group).as("g"), lit("0 as n")),
+        from(AllGroups),
+        AllGroups.group > Select(G.group.s, from(G), G.worker === worker)
       )
 
     val sql2 =
-      Select(min(JC.group).as("g"), from(JC), stateCond)
+      Select(
+        select(min(AllGroups.group).as("g"), lit("1 as n")),
+        from(AllGroups)
+      )
 
     val gcol = Column[String]("g", TableDef(""))
+    val gnum = Column[Int]("n", TableDef(""))
     val groups =
-      Select(select(gcol), from(union(sql1, sql2), "t0"), gcol.isNull.negate)
+      withCte(AllGroups -> AllGroups.selectAll)
+        .select(Select(gcol.s, from(union(sql1, sql2), "t0"), gcol.isNull.negate))
+        .orderBy(gnum.asc)
+        .limit(1)
 
-    // either 0, one or two results, but may be empty if RJob table is empty
-    groups.build.query[Ident].to[List].map(_.headOption)
+    val frag = groups.build
+    logger.trace(
+      s"nextGroupQuery: $frag  (now=${now.toMillis}, pause=${initialPause.millis})"
+    )
+
+    frag.query[Ident].option
   }
 
   private def stuckTriggerValue(t: RJob.Table, initialPause: Duration, now: Timestamp) =

modules/store/src/main/scala/docspell/store/records/RJobGroupUse.scala

@@ -36,4 +36,7 @@ object RJobGroupUse {
 
   def findGroup(workerId: Ident): ConnectionIO[Option[Ident]] =
     run(select(T.group), from(T), T.worker === workerId).query[Ident].option
+
+  def deleteAll: ConnectionIO[Int] =
+    DML.delete(T, T.group.isNotNull)
 }