store/copr: optimize copIterator by avoid start new goroutine

pkg/distsql/context/context.go

@@ -85,6 +85,9 @@ type DistSQLContext struct {
 	SessionAlias                string
 
 	ExecDetails *execdetails.SyncExecDetails
+
+	// Only one cop-reader can use lite worker. Using lite-worker in multiple readers will affect the concurrent execution of readers.
+	TryCopLiteWorker uint32
 }
 
 // AppendWarning appends the warning to the warning handler.

pkg/distsql/context/context_test.go

@@ -89,6 +89,7 @@ func TestContextDetach(t *testing.T) {
 		ReplicaClosestReadThreshold: 1,
 		ConnectionID:                1,
 		SessionAlias:                "c",
+		TryCopLiteWorker:            1,
 	}
 
 	obj.AppendWarning(errors.New("test warning"))

pkg/distsql/distsql.go

@@ -80,6 +80,7 @@ func Select(ctx context.Context, dctx *distsqlctx.DistSQLContext, kvReq *kv.Requ
 		EnabledRateLimitAction:     enabledRateLimitAction,
 		EventCb:                    eventCb,
 		EnableCollectExecutionInfo: config.GetGlobalConfig().Instance.EnableCollectExecutionInfo.Load(),
+		TryCopLiteWorker:           &dctx.TryCopLiteWorker,
 	}
 
 	if kvReq.StoreType == kv.TiFlash {

pkg/kv/kv.go

@@ -327,6 +327,7 @@ type ClientSendOption struct {
 	EnableCollectExecutionInfo bool
 	TiFlashReplicaRead         tiflash.ReplicaRead
 	AppendWarning              func(warn error)
+	TryCopLiteWorker           *uint32
 }
 
 // ReqTypes.

pkg/store/copr/copr_test/BUILD.bazel

@@ -8,15 +8,17 @@ go_test(
         "main_test.go",
     ],
     flaky = True,
-    shard_count = 3,
+    shard_count = 4,
     deps = [
         "//pkg/config",
         "//pkg/kv",
         "//pkg/resourcegroup/runaway",
         "//pkg/store/copr",
         "//pkg/store/mockstore",
+        "//pkg/testkit",
         "//pkg/testkit/testmain",
         "//pkg/testkit/testsetup",
+        "@com_github_pingcap_failpoint//:failpoint",
         "@com_github_pingcap_kvproto//pkg/meta_storagepb",
         "@com_github_pingcap_kvproto//pkg/resource_manager",
         "@com_github_stretchr_testify//require",

pkg/store/copr/copr_test/coprocessor_test.go

@@ -19,15 +19,18 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"testing"
 	"time"
 
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/kvproto/pkg/meta_storagepb"
 	rmpb "github.com/pingcap/kvproto/pkg/resource_manager"
 	"github.com/pingcap/tidb/pkg/kv"
 	"github.com/pingcap/tidb/pkg/resourcegroup/runaway"
 	"github.com/pingcap/tidb/pkg/store/copr"
 	"github.com/pingcap/tidb/pkg/store/mockstore"
+	"github.com/pingcap/tidb/pkg/testkit"
 	"github.com/stretchr/testify/require"
 	"github.com/tikv/client-go/v2/testutils"
 	pd "github.com/tikv/pd/client"
@@ -287,3 +290,21 @@ func TestBuildCopIteratorWithRunawayChecker(t *testing.T) {
 	require.Equal(t, concurrency, 1)
 	require.Equal(t, smallTaskConcurrency, 0)
 }
+
+func TestQueryWithConcurrentSmallCop(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	// Test for https://github.com/pingcap/tidb/pull/57522#discussion_r1875515863
+	tk.MustExec("create table t1 (id int key, b int, c int, index idx_b(b)) partition by hash(id) partitions 10;")
+	for i := 0; i < 10; i++ {
+		tk.MustExec(fmt.Sprintf("insert into t1 values (%v, %v, %v)", i, i, i))
+	}
+
+	tk.MustExec("set @@tidb_distsql_scan_concurrency=15")
+	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/store/mockstore/unistore/unistoreRPCSlowCop", `return(200)`))
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	tk.MustQueryWithContext(ctx, "select sum(c) from t1 use index (idx_b) where b < 10;")
+	cancel()
+	require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/pkg/store/mockstore/unistore/unistoreRPCSlowCop"))
+}