Panic : Multi-column Vindex on Gen4

[harshit-gangal]

If multi-column vindex is defined on a table, Gen4 planner panic on it when using it on select query.

 panic: interface conversion: *vindexes.RegionJSON is not vindexes.SingleColumn: missing method Map

potential fix

diff --git a/go/vt/vtgate/planbuilder/routetree.go b/go/vt/vtgate/planbuilder/routetree.go
index 29bcb4d1fa..e460a46e1f 100644
--- a/go/vt/vtgate/planbuilder/routetree.go
+++ b/go/vt/vtgate/planbuilder/routetree.go
@@ -521,8 +521,11 @@ func (rp *routeTree) pickBestAvailableVindex() {
        for _, v := range rp.vindexPreds {
                option := v.bestOption()
                if option != nil && (rp.selected == nil || less(option.cost, rp.selected.cost)) {
-                       rp.selected = option
-                       rp.routeOpCode = option.opcode
+                       // Only pick single column vindexes for now until we have support for multi column vindexes.
+                       if _, ok := option.foundVindex.(vindexes.SingleColumn); ok {
+                               rp.selected = option
+                               rp.routeOpCode = option.opcode
+                       }
                }
        }
 }

[harshit-gangal]

Fixed by #9061