[Exec](performance) change colocate execution parallel num

Author: HappenLee

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/distribute/worker/job/UnassignedScanBucketOlapTableJob.java

@@ -505,4 +505,40 @@ private List<DistributedPlanWorker> getWorkersByReplicas(Tablet tablet, long cat
         }
         return workers;
     }
+
+    @Override
+    protected int degreeOfParallelism(int maxParallel, boolean useLocalShuffleToAddParallel) {
+        Preconditions.checkArgument(maxParallel > 0, "maxParallel must be positive");
+        if (!fragment.getDataPartition().isPartitioned()) {
+            return 1;
+        }
+        if (fragment.queryCacheParam != null) {
+            return maxParallel;
+        }
+        if (scanNodes.size() == 1 && scanNodes.get(0) instanceof OlapScanNode) {
+            OlapScanNode olapScanNode = (OlapScanNode) scanNodes.get(0);
+            ConnectContext connectContext = statementContext.getConnectContext();
+            if (connectContext != null && olapScanNode.shouldUseOneInstance(connectContext)) {
+                return 1;
+            }
+        }
+
+        long tabletNum = 0;
+        for (ScanNode scanNode : scanNodes) {
+            if (scanNode instanceof OlapScanNode) {
+                OlapScanNode olapScanNode = (OlapScanNode) scanNode;
+                tabletNum = olapScanNode.getTotalTabletsNum();
+                break;
+            }
+        }
+
+        ConnectContext connectContext = statementContext.getConnectContext();
+        int colocateMaxParallelNum = 128;
+        if (connectContext != null) {
+            colocateMaxParallelNum = connectContext.getSessionVariable().colocateMaxParallelNum;
+        }
+
+        int maxParallelism = (int) Math.max(tabletNum, fragment.getParallelExecNum());
+        return Math.min(maxParallelism, colocateMaxParallelNum);
+    }
 }

fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java

@@ -163,6 +163,7 @@ public class SessionVariable implements Serializable, Writable {
     public static final String DISABLE_STREAMING_PREAGGREGATIONS = "disable_streaming_preaggregations";
     public static final String ENABLE_DISTINCT_STREAMING_AGGREGATION = "enable_distinct_streaming_aggregation";
     public static final String DISABLE_COLOCATE_PLAN = "disable_colocate_plan";
+    public static final String COLOCATE_MAX_PARALLEL_NUM = "colocate_max_parallel_num";
     public static final String ENABLE_BUCKET_SHUFFLE_JOIN = "enable_bucket_shuffle_join";
     public static final String PARALLEL_FRAGMENT_EXEC_INSTANCE_NUM = "parallel_fragment_exec_instance_num";
     public static final String PARALLEL_PIPELINE_TASK_NUM = "parallel_pipeline_task_num";
@@ -1287,6 +1288,9 @@ public void checkQuerySlotCount(String slotCnt) {
                         setter = "setFragmentInstanceNum", varType = VariableAnnotation.DEPRECATED)
     public int parallelExecInstanceNum = 8;
 
+    @VariableMgr.VarAttr(name = COLOCATE_MAX_PARALLEL_NUM, needForward = true, fuzzy = false)
+    public int colocateMaxParallelNum = 128;
+
     @VariableMgr.VarAttr(name = PARALLEL_PIPELINE_TASK_NUM, fuzzy = true, needForward = true,
                         setter = "setPipelineTaskNum")
     public int parallelPipelineTaskNum = 0;