[GitHub] [incubator-doris] imay commented on a change in pull request #851: Parallel fragment exec instance

[GitBox <gi...@apache.org>]

imay commented on a change in pull request #851: Parallel fragment exec instance
URL: https://github.com/apache/incubator-doris/pull/851#discussion_r270853216
 
 

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 File path: fe/src/main/java/org/apache/doris/qe/Coordinator.java
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 @@ -882,12 +889,60 @@ private void computeFragmentHosts() throws Exception {
         }
     }
 
-    //One fragment could only have one HashJoinNode
-    private boolean isColocateJoin(PlanNode node) {
-        if (Config.disable_colocate_join) {
+    private boolean needParallelInstance(PlanNode leftMostNode) {
+        if (getParallelExecInstanceNum() <= SessionVariable.MIN_EXEC_INSTANCE_NUM) {
             return false;
         }
 
+        if (leftMostNode instanceof OlapScanNode) {
+            OlapScanNode olapScanNode = (OlapScanNode) leftMostNode;
+
+            //case 1: the small table of broadcast join need not parallel
+            PlanFragment destFragment =  olapScanNode.getFragment().getDestFragment();
+            if (destFragment != null)  {
+                PlanNode destRootNode = destFragment.getPlanRoot();
+                if (destRootNode instanceof HashJoinNode) {
+                    HashJoinNode joinNode = (HashJoinNode) destRootNode;
+                    if (!joinNode.isShuffleJoin()) {
+                        LOG.debug("ScanNode {} for fragment {} need not parallel because of broadcast join",
+                        olapScanNode.getOlapTable().getName(), olapScanNode.getFragmentId());
+                        return false;
+                    }
+                }
 
 Review comment:
   Does this works? If the fragment is agg(hash(scan1, scan2)), for scan2, the RootNode of `destFragment` is `agg`.
   
   I think if it isn't easy to match this case, we can return true for it. 
   
   For broadcast join, I think the bigger influence is that the outer child will be parallel, and making it would need more hash table for inner child. So it's ok to scan parallel here

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