From 62c1241b7a9afc711df4f1da2dc042b6e4d487e9 Mon Sep 17 00:00:00 2001
From: Yiding Cui <winoros@gmail.com>
Date: Tue, 23 Oct 2018 14:24:28 +0800
Subject: [PATCH] executor: fix panic when limit is too large (#7936) (#8004)

---
 executor/executor_test.go | 4 ++++
 executor/sort.go          | 8 ++++----
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/executor/executor_test.go b/executor/executor_test.go
index c8c5ccd228188..dd038af049f7d 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -641,6 +641,10 @@ func (s *testSuite) TestSelectOrderBy(c *C) {
 	r = tk.MustQuery("select * from select_order_test order by name, id limit 1 offset 100;")
 	r.Check(testkit.Rows())
 
+	// Test limit exceeds int range.
+	r = tk.MustQuery("select id from select_order_test order by name, id limit 18446744073709551615;")
+	r.Check(testkit.Rows("1", "2"))
+
 	// Test multiple field
 	r = tk.MustQuery("select id, name from select_order_test where id = 1 group by id, name limit 1 offset 0;")
 	r.Check(testkit.Rows("1 hello"))
diff --git a/executor/sort.go b/executor/sort.go
index e77455dd87eed..40794a0dfc09d 100644
--- a/executor/sort.go
+++ b/executor/sort.go
@@ -222,7 +222,7 @@ func (e *SortExec) keyChunksLess(i, j int) bool {
 type TopNExec struct {
 	SortExec
 	limit      *plan.PhysicalLimit
-	totalLimit int
+	totalLimit uint64
 
 	chkHeap *topNChunkHeap
 }
@@ -298,7 +298,7 @@ func (e *TopNExec) Open(ctx context.Context) error {
 func (e *TopNExec) Next(ctx context.Context, chk *chunk.Chunk) error {
 	chk.Reset()
 	if !e.fetched {
-		e.totalLimit = int(e.limit.Offset + e.limit.Count)
+		e.totalLimit = e.limit.Offset + e.limit.Count
 		e.Idx = int(e.limit.Offset)
 		err := e.loadChunksUntilTotalLimit(ctx)
 		if err != nil {
@@ -326,7 +326,7 @@ func (e *TopNExec) loadChunksUntilTotalLimit(ctx context.Context) error {
 	e.rowChunks = chunk.NewList(e.retTypes(), e.maxChunkSize)
 	e.rowChunks.GetMemTracker().AttachTo(e.memTracker)
 	e.rowChunks.GetMemTracker().SetLabel("rowChunks")
-	for e.rowChunks.Len() < e.totalLimit {
+	for uint64(e.rowChunks.Len()) < e.totalLimit {
 		srcChk := e.children[0].newChunk()
 		err := e.children[0].Next(ctx, srcChk)
 		if err != nil {
@@ -354,7 +354,7 @@ const topNCompactionFactor = 4
 
 func (e *TopNExec) executeTopN(ctx context.Context) error {
 	heap.Init(e.chkHeap)
-	for len(e.rowPtrs) > e.totalLimit {
+	for uint64(len(e.rowPtrs)) > e.totalLimit {
 		// The number of rows we loaded may exceeds total limit, remove greatest rows by Pop.
 		heap.Pop(e.chkHeap)
 	}