From 896ddd82d6075b3294dddf9a3e459c8af6a2d645 Mon Sep 17 00:00:00 2001
From: Jerry Hu <mrhhsg@gmail.com>
Date: Tue, 28 Feb 2023 18:12:01 +0800
Subject: [PATCH] [fix](vec) avoid stack overflow when expr tree is too deep

---
 be/src/vec/exprs/vexpr.cpp         |  3 ---
 be/src/vec/exprs/vexpr_context.cpp | 20 +++++++++++++++++++-
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/be/src/vec/exprs/vexpr.cpp b/be/src/vec/exprs/vexpr.cpp
index f90993884d2d6f..4bf08bc6f5a2f9 100644
--- a/be/src/vec/exprs/vexpr.cpp
+++ b/be/src/vec/exprs/vexpr.cpp
@@ -85,9 +85,6 @@ VExpr::VExpr(const TypeDescriptor& type, bool is_slotref, bool is_nullable)
 }
 
 Status VExpr::prepare(RuntimeState* state, const RowDescriptor& row_desc, VExprContext* context) {
-    for (int i = 0; i < _children.size(); ++i) {
-        RETURN_IF_ERROR(_children[i]->prepare(state, row_desc, context));
-    }
     return Status::OK();
 }
 
diff --git a/be/src/vec/exprs/vexpr_context.cpp b/be/src/vec/exprs/vexpr_context.cpp
index 90332452026281..22e0e809bdfee6 100644
--- a/be/src/vec/exprs/vexpr_context.cpp
+++ b/be/src/vec/exprs/vexpr_context.cpp
@@ -49,7 +49,25 @@ doris::Status VExprContext::prepare(doris::RuntimeState* state,
                                     const doris::RowDescriptor& row_desc) {
     _prepared = true;
     _pool.reset(new MemPool());
-    return _root->prepare(state, row_desc, this);
+    std::stack<VExpr*> stack;
+    stack.push(_root);
+
+    std::vector<VExpr*> flatted;
+
+    while (!stack.empty()) {
+        auto* top = stack.top();
+        flatted.emplace_back(top);
+        stack.pop();
+        for (auto* child : top->children()) {
+            stack.push(child);
+        }
+    }
+
+    for (ssize_t i = flatted.size() - 1; i >= 0; --i) {
+        RETURN_IF_ERROR(flatted[i]->prepare(state, row_desc, this));
+    }
+
+    return Status::OK();
 }
 
 doris::Status VExprContext::open(doris::RuntimeState* state) {