*: support coprocessor cache for paging protocol

executor/copr_cache_test.go

@@ -53,9 +53,6 @@ func TestIntegrationCopCache(t *testing.T) {
 	tk.MustExec("use test")
 	tk.MustExec("create table t (a int primary key)")
 
-	// TODO(tiancaiamao) update the test and support cop cache for paging.
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	tblInfo, err := dom.InfoSchema().TableByName(model.NewCIStr("test"), model.NewCIStr("t"))
 	require.NoError(t, err)
 	tid := tblInfo.Meta().ID

planner/core/cbo_test.go

@@ -822,9 +822,6 @@ func TestLimitIndexEstimation(t *testing.T) {
 		SQL  string
 		Plan []string
 	}
-	// When paging is used, there is a 'paging:true' makes the explain output differ.
-	// IndexLookUp 0.00 root  paging:true
-	tk.MustExec("set @@tidb_enable_paging = off")
 
 	analyzeSuiteData := core.GetAnalyzeSuiteData()
 	analyzeSuiteData.GetTestCases(t, &input, &output)

planner/core/integration_test.go

@@ -177,9 +177,6 @@ func TestPushLimitDownIndexLookUpReader(t *testing.T) {
 	tk.MustExec("insert into tbl values(1,1,1),(2,2,2),(3,3,3),(4,4,4),(5,5,5)")
 	tk.MustExec("analyze table tbl")
 
-	// When paging is enabled, there would be a 'paging: true' in the explain result.
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	var input []string
 	var output []struct {
 		SQL  string
@@ -3685,9 +3682,6 @@ func TestExtendedStatsSwitch(t *testing.T) {
 		"1.000000 1",
 	))
 
-	// When paging is enabled, there would be a 'paging: true' in the explain result.
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	// Estimated index scan count is 4 using extended stats.
 	tk.MustQuery("explain format = 'brief' select * from t use index(b) where a > 3 order by b limit 1").Check(testkit.Rows(
 		"Limit 1.00 root  offset:0, count:1",
@@ -4557,9 +4551,6 @@ func TestLimitIndexLookUpKeepOrder(t *testing.T) {
 	tk.MustExec("drop table if exists t;")
 	tk.MustExec("create table t(a int, b int, c int, d int, index idx(a,b,c));")
 
-	// When paging is enabled, there would be a 'paging: true' in the explain result.
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	var input []string
 	var output []struct {
 		SQL  string
@@ -4786,9 +4777,6 @@ func TestMultiColMaxOneRow(t *testing.T) {
 	tk.MustExec("create table t1(a int)")
 	tk.MustExec("create table t2(a int, b int, c int, primary key(a,b))")
 
-	// When paging is enabled, there would be a 'paging: true' in the explain result.
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	var input []string
 	var output []struct {
 		SQL  string
@@ -5561,8 +5549,6 @@ func TestPreferRangeScanForUnsignedIntHandle(t *testing.T) {
 
 	// Default RPC encoding may cause statistics explain result differ and then the test unstable.
 	tk.MustExec("set @@tidb_enable_chunk_rpc = on")
-	// When paging is enabled, there would be a 'paging: true' in the explain result.
-	tk.MustExec("set @@tidb_enable_paging = off")
 
 	var input []string
 	var output []struct {
@@ -5602,9 +5588,6 @@ func TestIssue27083(t *testing.T) {
 	require.Nil(t, do.StatsHandle().DumpStatsDeltaToKV(handle.DumpAll))
 	tk.MustExec("analyze table t")
 
-	// When paging is enabled, there would be a 'paging: true' in the explain result.
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	var input []string
 	var output []struct {
 		SQL  string

planner/core/physical_plan_test.go

@@ -538,10 +538,6 @@ func TestEliminateMaxOneRow(t *testing.T) {
 	tk.MustExec("create table t2(a int(11) DEFAULT NULL, b int(11) DEFAULT NULL)")
 	tk.MustExec("create table t3(a int(11) DEFAULT NULL, b int(11) DEFAULT NULL, c int(11) DEFAULT NULL, UNIQUE KEY idx_abc (a, b, c))")
 
-	// When paging is used, there is a 'paging:true' makes the explain output differ.
-	// IndexLookUp 0.00 root  paging:true
-	tk.MustExec("set @@tidb_enable_paging = off")
-
 	for i, ts := range input {
 		testdata.OnRecord(func() {
 			output[i].SQL = ts

planner/core/task.go

@@ -667,7 +667,7 @@ func calcPagingCost(ctx sessionctx.Context, indexPlan PhysicalPlan, expectCnt ui
 
 	// we want the diff between idxCst and pagingCst here,
 	// however, the idxCst does not contain seekFactor, so a seekFactor needs to be removed
-	return pagingCst - sessVars.GetSeekFactor(nil)
+	return math.Max(pagingCst-sessVars.GetSeekFactor(nil), 0)
 }
 
 func (t *rootTask) convertToRootTask(_ sessionctx.Context) *rootTask {

store/copr/coprocessor.go

@@ -712,15 +712,15 @@ func (worker *copIteratorWorker) handleTaskOnce(bo *Backoffer, task *copTask, ch
 	var cacheKey []byte
 	var cacheValue *coprCacheValue
 
-	// TODO: cache paging copr
 	// If there are many ranges, it is very likely to be a TableLookupRequest. They are not worth to cache since
 	// computing is not the main cost. Ignore such requests directly to avoid slowly building the cache key.
-	if task.cmdType == tikvrpc.CmdCop && !task.paging && worker.store.coprCache != nil && worker.req.Cacheable && worker.store.coprCache.CheckRequestAdmission(len(copReq.Ranges)) {
+	if task.cmdType == tikvrpc.CmdCop && worker.store.coprCache != nil && worker.req.Cacheable && worker.store.coprCache.CheckRequestAdmission(len(copReq.Ranges)) {
 		cKey, err := coprCacheBuildKey(&copReq)
 		if err == nil {
 			cacheKey = cKey
 			cValue := worker.store.coprCache.Get(cKey)
 			copReq.IsCacheEnabled = true
+
 			if cValue != nil && cValue.RegionID == task.region.GetID() && cValue.TimeStamp <= worker.req.StartTs {
 				// Append cache version to the request to skip Coprocessor computation if possible
 				// when request result is cached
@@ -779,7 +779,7 @@ func (worker *copIteratorWorker) handleTaskOnce(bo *Backoffer, task *copTask, ch
 	metrics.TiKVCoprocessorHistogram.WithLabelValues(storeID, strconv.FormatBool(staleRead)).Observe(costTime.Seconds())
 
 	if worker.req.Paging {
-		return worker.handleCopPagingResult(bo, rpcCtx, &copResponse{pbResp: resp.Resp.(*coprocessor.Response)}, task, ch, costTime)
+		return worker.handleCopPagingResult(bo, rpcCtx, &copResponse{pbResp: resp.Resp.(*coprocessor.Response)}, cacheKey, cacheValue, task, ch, costTime)
 	}
 
 	// Handles the response for non-paging copTask.
@@ -848,8 +848,8 @@ func appendScanDetail(logStr string, columnFamily string, scanInfo *kvrpcpb.Scan
 	return logStr
 }
 
-func (worker *copIteratorWorker) handleCopPagingResult(bo *Backoffer, rpcCtx *tikv.RPCContext, resp *copResponse, task *copTask, ch chan<- *copResponse, costTime time.Duration) ([]*copTask, error) {
-	remainedTasks, err := worker.handleCopResponse(bo, rpcCtx, resp, nil, nil, task, ch, nil, costTime)
+func (worker *copIteratorWorker) handleCopPagingResult(bo *Backoffer, rpcCtx *tikv.RPCContext, resp *copResponse, cacheKey []byte, cacheValue *coprCacheValue, task *copTask, ch chan<- *copResponse, costTime time.Duration) ([]*copTask, error) {
+	remainedTasks, err := worker.handleCopResponse(bo, rpcCtx, resp, cacheKey, cacheValue, task, ch, nil, costTime)
 	if err != nil || len(remainedTasks) != 0 {
 		// If there is region error or lock error, keep the paging size and retry.
 		for _, remainedTask := range remainedTasks {
@@ -954,6 +954,22 @@ func (worker *copIteratorWorker) handleCopResponse(bo *Backoffer, rpcCtx *tikv.R
 		data := make([]byte, len(cacheValue.Data))
 		copy(data, cacheValue.Data)
 		resp.pbResp.Data = data
+		if worker.req.Paging {
+			var start, end []byte
+			if cacheValue.PageStart != nil {
+				start = make([]byte, len(cacheValue.PageStart))
+				copy(start, cacheValue.PageStart)
+			}
+			if cacheValue.PageEnd != nil {
+				end = make([]byte, len(cacheValue.PageEnd))
+				copy(end, cacheValue.PageEnd)
+			}
+			// When paging protocol is used, the response key range is part of the cache data.
+			resp.pbResp.Range = &coprocessor.KeyRange{
+				Start: start,
+				End:   end,
+			}
+		}
 		resp.detail.CoprCacheHit = true
 	} else {
 		// Cache not hit or cache hit but not valid: update the cache if the response can be cached.
@@ -969,6 +985,12 @@ func (worker *copIteratorWorker) handleCopResponse(bo *Backoffer, rpcCtx *tikv.R
 						RegionID:          task.region.GetID(),
 						RegionDataVersion: resp.pbResp.CacheLastVersion,
 					}
+					// When paging protocol is used, the response key range is part of the cache data.
+					if r := resp.pbResp.GetRange(); r != nil {
+						newCacheValue.PageStart = append([]byte{}, r.GetStart()...)
+						newCacheValue.PageEnd = append([]byte{}, r.GetEnd()...)
+					}
+
 					worker.store.coprCache.Set(cacheKey, &newCacheValue)
 				}
 			}

store/copr/coprocessor_cache.go

@@ -41,6 +41,10 @@ type coprCacheValue struct {
 	TimeStamp         uint64
 	RegionID          uint64
 	RegionDataVersion uint64
+
+	// Used in coprocessor paging protocol
+	PageStart []byte
+	PageEnd   []byte
 }
 
 func (v *coprCacheValue) String() string {
@@ -54,7 +58,7 @@ func (v *coprCacheValue) String() string {
 const coprCacheValueSize = int(unsafe.Sizeof(coprCacheValue{}))
 
 func (v *coprCacheValue) Len() int {
-	return coprCacheValueSize + len(v.Key) + len(v.Data)
+	return coprCacheValueSize + len(v.Key) + len(v.Data) + len(v.PageStart) + len(v.PageEnd)
 }
 
 func newCoprCache(config *config.CoprocessorCache) (*coprCache, error) {
@@ -108,6 +112,9 @@ func coprCacheBuildKey(copReq *coprocessor.Request) ([]byte, error) {
 		}
 		totalLength += 2 + len(r.Start) + 2 + len(r.End)
 	}
+	if copReq.PagingSize > 0 {
+		totalLength += 1
+	}
 
 	key := make([]byte, totalLength)
 
@@ -141,6 +148,11 @@ func coprCacheBuildKey(copReq *coprocessor.Request) ([]byte, error) {
 		dest += len(r.End)
 	}
 
+	// 1 byte when use paging protocol
+	if copReq.PagingSize > 0 {
+		key[dest] = 1
+	}
+
 	return key, nil
 }
 

store/copr/coprocessor_cache_test.go

@@ -155,8 +155,8 @@ func TestCacheValueLen(t *testing.T) {
 		RegionID:          0x1,
 		RegionDataVersion: 0x3,
 	}
-	// 72 = (8 byte pointer + 8 byte for length + 8 byte for cap) * 2 + 8 byte * 3
-	require.Equal(t, 72, v.Len())
+	// 120 = (8 byte pointer + 8 byte for length + 8 byte for cap) * 4 + 8 byte * 3
+	require.Equal(t, 120, v.Len())
 
 	v = coprCacheValue{
 		Key:               []byte("foobar"),
@@ -165,7 +165,17 @@ func TestCacheValueLen(t *testing.T) {
 		RegionID:          0x1,
 		RegionDataVersion: 0x3,
 	}
-	require.Equal(t, 72+len(v.Key)+len(v.Data), v.Len())
+	require.Equal(t, 120+len(v.Key)+len(v.Data), v.Len())
+
+	v = coprCacheValue{
+		Key:               []byte("foobar"),
+		Data:              []byte("12345678"),
+		TimeStamp:         0x123,
+		RegionID:          0x1,
+		RegionDataVersion: 0x3,
+		PageEnd:           []byte("3235"),
+	}
+	require.Equal(t, 120+len(v.Key)+len(v.Data)+len(v.PageEnd), v.Len())
 }
 
 func TestGetSet(t *testing.T) {