executor: disable paging for small limit (#41120)

close #40741
pingcap · Feb 7, 2023 · 98aff8c · 98aff8c
1 parent 79a5d3b
commit 98aff8c
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Showing 5 changed files with 42 additions and 3 deletions.
diff --git a/distsql/request_builder.go b/distsql/request_builder.go
@@ -159,6 +159,7 @@ func (builder *RequestBuilder) SetDAGRequest(dag *tipb.DAGRequest) *RequestBuild
 		if limit != nil && limit.Limit < estimatedRegionRowCount {
 			builder.Request.Concurrency = 1
 		}
+		builder.Request.LimitSize = limit.GetLimit()
 	}
 	return builder
 }

diff --git a/distsql/request_builder_test.go b/distsql/request_builder_test.go
@@ -676,6 +676,7 @@ func TestScanLimitConcurrency(t *testing.T) {
 				Build()
 			require.NoError(t, err)
 			require.Equal(t, tt.concurrency, actual.Concurrency)
+			require.Equal(t, actual.LimitSize, tt.limit)
 		})
 	}
 }

diff --git a/kv/kv.go b/kv/kv.go
@@ -573,6 +573,8 @@ type Request struct {
 	StoreBatchSize int
 	// ResourceGroupName is the name of the bind resource group.
 	ResourceGroupName string
+	// LimitSize indicates whether the request is scan and limit
+	LimitSize uint64
 }
 
 // CoprRequestAdjuster is used to check and adjust a copr request according to specific rules.

diff --git a/store/copr/coprocessor.go b/store/copr/coprocessor.go
@@ -402,7 +402,13 @@ func buildCopTasks(bo *Backoffer, ranges *KeyRanges, opt *buildCopTaskOpt) ([]*c
 			}
 			i = nextI
 			if req.Paging.Enable {
-				pagingSize = paging.GrowPagingSize(pagingSize, req.Paging.MaxPagingSize)
+				if req.LimitSize != 0 && req.LimitSize < pagingSize {
+					// disable paging for small limit.
+					task.paging = false
+					task.pagingSize = 0
+				} else {
+					pagingSize = paging.GrowPagingSize(pagingSize, req.Paging.MaxPagingSize)
+				}
 			}
 		}
 	}

diff --git a/store/copr/coprocessor_test.go b/store/copr/coprocessor_test.go
@@ -514,8 +514,6 @@ func TestBuildPagingTasks(t *testing.T) {
 	req := &kv.Request{}
 	req.Paging.Enable = true
 	req.Paging.MinPagingSize = paging.MinPagingSize
-	flashReq := &kv.Request{}
-	flashReq.StoreType = kv.TiFlash
 	tasks, err := buildTestCopTasks(bo, cache, buildCopRanges("a", "c"), req, nil)
 	require.NoError(t, err)
 	require.Len(t, tasks, 1)
@@ -525,6 +523,37 @@ func TestBuildPagingTasks(t *testing.T) {
 	require.Equal(t, tasks[0].pagingSize, paging.MinPagingSize)
 }
 
+func TestBuildPagingTasksDisablePagingForSmallLimit(t *testing.T) {
+	mockClient, cluster, pdClient, err := testutils.NewMockTiKV("", nil)
+	require.NoError(t, err)
+	defer func() {
+		pdClient.Close()
+		err = mockClient.Close()
+		require.NoError(t, err)
+	}()
+	_, regionIDs, _ := testutils.BootstrapWithMultiRegions(cluster, []byte("g"), []byte("n"), []byte("t"))
+
+	pdCli := tikv.NewCodecPDClient(tikv.ModeTxn, pdClient)
+	defer pdCli.Close()
+
+	cache := NewRegionCache(tikv.NewRegionCache(pdCli))
+	defer cache.Close()
+
+	bo := backoff.NewBackofferWithVars(context.Background(), 3000, nil)
+
+	req := &kv.Request{}
+	req.Paging.Enable = true
+	req.Paging.MinPagingSize = paging.MinPagingSize
+	req.LimitSize = 1
+	tasks, err := buildTestCopTasks(bo, cache, buildCopRanges("a", "c"), req, nil)
+	require.NoError(t, err)
+	require.Len(t, tasks, 1)
+	require.Len(t, tasks, 1)
+	taskEqual(t, tasks[0], regionIDs[0], 0, "a", "c")
+	require.False(t, tasks[0].paging)
+	require.Equal(t, tasks[0].pagingSize, uint64(0))
+}
+
 func toCopRange(r kv.KeyRange) *coprocessor.KeyRange {
 	coprRange := coprocessor.KeyRange{}
 	coprRange.Start = r.StartKey