server: add experimental flag for using shared buffer in transacton write

server/config/config.go

@@ -177,6 +177,10 @@ type ServerConfig struct {
 	// Currently all etcd memory gets mlocked, but in future the flag can
 	// be refined to mlock in-use area of bbolt only.
 	ExperimentalMemoryMlock bool `json:"experimental-memory-mlock"`
+
+	// ExperimentalTxnModeWriteWithSharedBuffer enable write transaction to use
+	// a shared buffer in its readonly check operations.
+	ExperimentalTxnModeWriteWithSharedBuffer bool `json:"experimental-txn-mode-write-with-shared-buffer"`
 }
 
 // VerifyBootstrap sanity-checks the initial config for bootstrap case

server/embed/config.go

@@ -355,6 +355,9 @@ type Config struct {
 	// Currently all etcd memory gets mlocked, but in future the flag can
 	// be refined to mlock in-use area of bbolt only.
 	ExperimentalMemoryMlock bool `json:"experimental-memory-mlock"`
+
+	// ExperimentalTxnModeWriteWithSharedBuffer enables write transaction to use a shared buffer in its readonly check operations.
+	ExperimentalTxnModeWriteWithSharedBuffer bool `json:"experimental-txn-mode-write-with-shared-buffer"`
 }
 
 // configYAML holds the config suitable for yaml parsing
@@ -444,8 +447,9 @@ func NewConfig() *Config {
 		LogLevel:          logutil.DefaultLogLevel,
 		EnableGRPCGateway: true,
 
-		ExperimentalDowngradeCheckTime: DefaultDowngradeCheckTime,
+		ExperimentalDowngradeCheckTime:           DefaultDowngradeCheckTime,
-		ExperimentalMemoryMlock:        false,
+		ExperimentalMemoryMlock:                  false,
+		ExperimentalTxnModeWriteWithSharedBuffer: true,
 	}
 	cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
 	return cfg

server/embed/etcd.go

@@ -163,56 +163,57 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 	backendFreelistType := parseBackendFreelistType(cfg.BackendFreelistType)
 
 	srvcfg := config.ServerConfig{
-		Name:                        cfg.Name,
+		Name:                                     cfg.Name,
-		ClientURLs:                  cfg.ACUrls,
+		ClientURLs:                               cfg.ACUrls,
-		PeerURLs:                    cfg.APUrls,
+		PeerURLs:                                 cfg.APUrls,
-		DataDir:                     cfg.Dir,
+		DataDir:                                  cfg.Dir,
-		DedicatedWALDir:             cfg.WalDir,
+		DedicatedWALDir:                          cfg.WalDir,
-		SnapshotCount:               cfg.SnapshotCount,
+		SnapshotCount:                            cfg.SnapshotCount,
-		SnapshotCatchUpEntries:      cfg.SnapshotCatchUpEntries,
+		SnapshotCatchUpEntries:                   cfg.SnapshotCatchUpEntries,
-		MaxSnapFiles:                cfg.MaxSnapFiles,
+		MaxSnapFiles:                             cfg.MaxSnapFiles,
-		MaxWALFiles:                 cfg.MaxWalFiles,
+		MaxWALFiles:                              cfg.MaxWalFiles,
-		InitialPeerURLsMap:          urlsmap,
+		InitialPeerURLsMap:                       urlsmap,
-		InitialClusterToken:         token,
+		InitialClusterToken:                      token,
-		DiscoveryURL:                cfg.Durl,
+		DiscoveryURL:                             cfg.Durl,
-		DiscoveryProxy:              cfg.Dproxy,
+		DiscoveryProxy:                           cfg.Dproxy,
-		NewCluster:                  cfg.IsNewCluster(),
+		NewCluster:                               cfg.IsNewCluster(),
-		PeerTLSInfo:                 cfg.PeerTLSInfo,
+		PeerTLSInfo:                              cfg.PeerTLSInfo,
-		TickMs:                      cfg.TickMs,
+		TickMs:                                   cfg.TickMs,
-		ElectionTicks:               cfg.ElectionTicks(),
+		ElectionTicks:                            cfg.ElectionTicks(),
-		InitialElectionTickAdvance:  cfg.InitialElectionTickAdvance,
+		InitialElectionTickAdvance:               cfg.InitialElectionTickAdvance,
-		AutoCompactionRetention:     autoCompactionRetention,
+		AutoCompactionRetention:                  autoCompactionRetention,
-		AutoCompactionMode:          cfg.AutoCompactionMode,
+		AutoCompactionMode:                       cfg.AutoCompactionMode,
-		QuotaBackendBytes:           cfg.QuotaBackendBytes,
+		QuotaBackendBytes:                        cfg.QuotaBackendBytes,
-		BackendBatchLimit:           cfg.BackendBatchLimit,
+		BackendBatchLimit:                        cfg.BackendBatchLimit,
-		BackendFreelistType:         backendFreelistType,
+		BackendFreelistType:                      backendFreelistType,
-		BackendBatchInterval:        cfg.BackendBatchInterval,
+		BackendBatchInterval:                     cfg.BackendBatchInterval,
-		MaxTxnOps:                   cfg.MaxTxnOps,
+		MaxTxnOps:                                cfg.MaxTxnOps,
-		MaxRequestBytes:             cfg.MaxRequestBytes,
+		MaxRequestBytes:                          cfg.MaxRequestBytes,
-		SocketOpts:                  cfg.SocketOpts,
+		SocketOpts:                               cfg.SocketOpts,
-		StrictReconfigCheck:         cfg.StrictReconfigCheck,
+		StrictReconfigCheck:                      cfg.StrictReconfigCheck,
-		ClientCertAuthEnabled:       cfg.ClientTLSInfo.ClientCertAuth,
+		ClientCertAuthEnabled:                    cfg.ClientTLSInfo.ClientCertAuth,
-		AuthToken:                   cfg.AuthToken,
+		AuthToken:                                cfg.AuthToken,
-		BcryptCost:                  cfg.BcryptCost,
+		BcryptCost:                               cfg.BcryptCost,
-		TokenTTL:                    cfg.AuthTokenTTL,
+		TokenTTL:                                 cfg.AuthTokenTTL,
-		CORS:                        cfg.CORS,
+		CORS:                                     cfg.CORS,
-		HostWhitelist:               cfg.HostWhitelist,
+		HostWhitelist:                            cfg.HostWhitelist,
-		InitialCorruptCheck:         cfg.ExperimentalInitialCorruptCheck,
+		InitialCorruptCheck:                      cfg.ExperimentalInitialCorruptCheck,
-		CorruptCheckTime:            cfg.ExperimentalCorruptCheckTime,
+		CorruptCheckTime:                         cfg.ExperimentalCorruptCheckTime,
-		PreVote:                     cfg.PreVote,
+		PreVote:                                  cfg.PreVote,
-		Logger:                      cfg.logger,
+		Logger:                                   cfg.logger,
-		LoggerConfig:                cfg.loggerConfig,
+		LoggerConfig:                             cfg.loggerConfig,
-		LoggerCore:                  cfg.loggerCore,
+		LoggerCore:                               cfg.loggerCore,
-		LoggerWriteSyncer:           cfg.loggerWriteSyncer,
+		LoggerWriteSyncer:                        cfg.loggerWriteSyncer,
-		ForceNewCluster:             cfg.ForceNewCluster,
+		ForceNewCluster:                          cfg.ForceNewCluster,
-		EnableGRPCGateway:           cfg.EnableGRPCGateway,
+		EnableGRPCGateway:                        cfg.EnableGRPCGateway,
-		UnsafeNoFsync:               cfg.UnsafeNoFsync,
+		UnsafeNoFsync:                            cfg.UnsafeNoFsync,
-		EnableLeaseCheckpoint:       cfg.ExperimentalEnableLeaseCheckpoint,
+		EnableLeaseCheckpoint:                    cfg.ExperimentalEnableLeaseCheckpoint,
-		CompactionBatchLimit:        cfg.ExperimentalCompactionBatchLimit,
+		CompactionBatchLimit:                     cfg.ExperimentalCompactionBatchLimit,
-		WatchProgressNotifyInterval: cfg.ExperimentalWatchProgressNotifyInterval,
+		WatchProgressNotifyInterval:              cfg.ExperimentalWatchProgressNotifyInterval,
-		DowngradeCheckTime:          cfg.ExperimentalDowngradeCheckTime,
+		DowngradeCheckTime:                       cfg.ExperimentalDowngradeCheckTime,
-		WarningApplyDuration:        cfg.ExperimentalWarningApplyDuration,
+		WarningApplyDuration:                     cfg.ExperimentalWarningApplyDuration,
-		ExperimentalMemoryMlock:     cfg.ExperimentalMemoryMlock,
+		ExperimentalMemoryMlock:                  cfg.ExperimentalMemoryMlock,
+		ExperimentalTxnModeWriteWithSharedBuffer: cfg.ExperimentalTxnModeWriteWithSharedBuffer,
 	}
 	print(e.cfg.logger, *cfg, srvcfg, memberInitialized)
 	if e.Server, err = etcdserver.NewServer(srvcfg); err != nil {

server/etcdmain/config.go

@@ -267,6 +267,7 @@ func newConfig() *config {
 	fs.DurationVar(&cfg.ec.ExperimentalDowngradeCheckTime, "experimental-downgrade-check-time", cfg.ec.ExperimentalDowngradeCheckTime, "Duration of time between two downgrade status check.")
 	fs.DurationVar(&cfg.ec.ExperimentalWarningApplyDuration, "experimental-warning-apply-duration", cfg.ec.ExperimentalWarningApplyDuration, "Time duration after which a warning is generated if request takes more time.")
 	fs.BoolVar(&cfg.ec.ExperimentalMemoryMlock, "experimental-memory-mlock", cfg.ec.ExperimentalMemoryMlock, "Enable to enforce etcd pages (in particular bbolt) to stay in RAM.")
+	fs.BoolVar(&cfg.ec.ExperimentalTxnModeWriteWithSharedBuffer, "experimental-txn-mode-write-with-shared-buffer", true, "Enable the write transaction to use a shared buffer in its readonly check operations.")
 
 	// unsafe
 	fs.BoolVar(&cfg.ec.UnsafeNoFsync, "unsafe-no-fsync", false, "Disables fsync, unsafe, will cause data loss.")

server/etcdmain/help.go

@@ -220,6 +220,8 @@ Experimental feature:
     Duration of periodical watch progress notification.
   --experimental-warning-apply-duration '100ms'
 	Warning is generated if requests take more than this duration.
+  --experimental-txn-mode-write-with-shared-buffer 'true'
+    Enable the write transaction to use a shared buffer in its readonly check operations.
 
 Unsafe feature:
   --force-new-cluster 'false'

server/etcdserver/apply.go

@@ -438,7 +438,7 @@ func (a *applierV3backend) Txn(ctx context.Context, rt *pb.TxnRequest) (*pb.TxnR
 	// When the transaction contains write operations, we use ReadTx instead of
 	// ConcurrentReadTx to avoid extra overhead of copying buffer.
 	var txn mvcc.TxnWrite
-	if isWrite {
+	if isWrite && a.s.Cfg.ExperimentalTxnModeWriteWithSharedBuffer {
 		txn = mvcc.NewReadOnlyTxnWrite(a.s.KV().Read(mvcc.SharedBufReadTxMode, trace))
 	} else {
 		txn = mvcc.NewReadOnlyTxnWrite(a.s.KV().Read(mvcc.ConcurrentReadTxMode, trace))