Estimate number of launched workers from gather node

If the count is not available in the node itself.

Fixes #578

src/enums.ts

@@ -127,6 +127,7 @@ export enum NodeProp {
   AVERAGE_IO_WRITE_TIME = "*I/O Write Speed (exclusive)",
 
   WORKERS_PLANNED_BY_GATHER = "*Workers Planned By Gather",
+  WORKERS_LAUNCHED_BY_GATHER = "*Workers Launched By Gather",
 
   CTE_SCAN = "CTE Scan",
   CTE_NAME = "CTE Name",

src/node.ts

@@ -245,6 +245,9 @@ export default function useNode(
     if (node[NodeProp.WORKERS_LAUNCHED]) {
       return node[NodeProp.WORKERS_LAUNCHED] as number
     }
+    if (node[NodeProp.WORKERS_LAUNCHED_BY_GATHER]) {
+      return node[NodeProp.WORKERS_LAUNCHED_BY_GATHER] as number
+    }
     const workers = node[NodeProp.WORKERS] as Worker[]
     return workers ? workers.length : NaN
   })

src/services/plan-service.ts

@@ -89,6 +89,9 @@ export class PlanService {
         child[NodeProp.WORKERS_PLANNED_BY_GATHER] =
           node[NodeProp.WORKERS_PLANNED] ||
           node[NodeProp.WORKERS_PLANNED_BY_GATHER]
+        child[NodeProp.WORKERS_LAUNCHED_BY_GATHER] =
+          node[NodeProp.WORKERS_LAUNCHED] ||
+          node[NodeProp.WORKERS_LAUNCHED_BY_GATHER]
       }
       if (this.isCTE(child)) {
         plan.ctes.push(child)