Wrap tablets introduction in experimental setting

Tablets are still experimental in ScyllaDB and
changes in the tablets format are possible.

cluster.go

@@ -244,6 +244,9 @@ type ClusterConfig struct {
 	// internal config for testing
 	disableControlConn bool
 	disableInit        bool
+
+	// If true tablet feature is enabled
+	experimentalTabletsEnabled bool
 }
 
 type Dialer interface {
@@ -277,6 +280,7 @@ func NewCluster(hosts ...string) *ClusterConfig {
 		ConvictionPolicy:       &SimpleConvictionPolicy{},
 		ReconnectionPolicy:     &ConstantReconnectionPolicy{MaxRetries: 3, Interval: 1 * time.Second},
 		WriteCoalesceWaitTime:  200 * time.Microsecond,
+		experimentalTabletsEnabled: false,
 	}
 
 	return cfg
@@ -314,6 +318,10 @@ func (cfg *ClusterConfig) filterHost(host *HostInfo) bool {
 	return !(cfg.HostFilter == nil || cfg.HostFilter.Accept(host))
 }
 
+func (cfg *ClusterConfig) EnableExperimentalTablets() {
+	cfg.experimentalTabletsEnabled = true
+}
+
 var (
 	ErrNoHosts              = errors.New("no hosts provided")
 	ErrNoConnectionsStarted = errors.New("no connections were made when creating the session")

connectionpool.go

@@ -27,6 +27,7 @@ type SetPartitioner interface {
 }
 
 // interface to implement to receive the tablets value
+// Experimental, this interface and use may change
 type SetTablets interface {
 	SetTablets(tablets []*TabletInfo)
 }

host_source.go

@@ -472,11 +472,13 @@ func (h *HostInfo) ScyllaShardAwarePortTLS() uint16 {
 	return h.scyllaShardAwarePortTLS
 }
 
+// Experimental, this interface and use may change
 type ReplicaInfo struct {
 	hostId  UUID
 	shardId int
 }
 
+// Experimental, this interface and use may change
 type TabletInfo struct {
 	mu           sync.RWMutex
 	keyspaceName string
@@ -576,7 +578,8 @@ type ringDescriber struct {
 	mu              sync.Mutex
 	prevHosts       []*HostInfo
 	prevPartitioner string
-	prevTablets     []*TabletInfo
+	// Experimental, this interface and use may change
+	prevTablets []*TabletInfo
 }
 
 // Returns true if we are using system_schema.keyspaces instead of system.schema_keyspaces
@@ -719,6 +722,7 @@ func (s *Session) hostInfoFromMap(row map[string]interface{}, host *HostInfo) (*
 
 // Given a map that represents a row from system.tablets
 // return as much information as we can in *TabletInfo
+// Experimental, this interface and use may change
 func (s *Session) tabletInfoFromMap(row map[string]interface{}, tablet *TabletInfo) (*TabletInfo, error) {
 	const assertErrorMsg = "Missing column %s in tablet description"
 	var ok bool
@@ -884,6 +888,7 @@ func (r *ringDescriber) getClusterPeerInfo(localHost *HostInfo) ([]*HostInfo, er
 }
 
 // Ask the control node for info about tablets
+// Experimental, this interface and use may change
 func (r *ringDescriber) getSystemTabletsInfo() ([]*TabletInfo, error) {
 	if r.session.control == nil {
 		return nil, errNoControl
@@ -921,6 +926,7 @@ func (r *ringDescriber) getSystemTabletsInfo() ([]*TabletInfo, error) {
 }
 
 // Return true if the tablet is valid
+// Experimental, this interface and use may change
 func isValidTablet(tablet *TabletInfo) bool {
 	return tablet.replicas != nil && len(tablet.replicas) != 0 && tablet.tableName != ""
 }
@@ -959,6 +965,7 @@ func (r *ringDescriber) GetHosts() ([]*HostInfo, string, error) {
 }
 
 // GetTablets returns a list of tablets found via queries to system.tablets
+// Experimental, this interface and use may change
 func (r *ringDescriber) GetTablets() ([]*TabletInfo, error) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
@@ -973,6 +980,7 @@ func (r *ringDescriber) GetTablets() ([]*TabletInfo, error) {
 }
 
 // True if experimental feature "tablets" is enabled and it is possible to query system.tablets
+// Experimental, this interface and use may change
 func (r *ringDescriber) UsesTablets() bool {
 	_, err := r.GetTablets()
 	if err != nil {
@@ -1091,6 +1099,7 @@ func refreshRing(r *ringDescriber) error {
 	return nil
 }
 
+// Experimental, this interface and use may change
 func refreshTablets(r *ringDescriber) error {
 	tablets, err := r.GetTablets()
 	if err != nil {
@@ -1216,6 +1225,7 @@ func (d *refreshDebouncer) stop() {
 }
 
 // used to refresh tablets every x seconds
+// Experimental, this interface and use may change
 type tabletRefresher struct {
 	mu          sync.Mutex
 	ticker      *time.Ticker

metadata_scylla.go

@@ -134,11 +134,13 @@ type IndexMetadata struct {
 }
 
 // TabletsMetadata holds metadata for tablet list
+// Experimental, this interface and use may change
 type TabletsMetadata struct {
 	Tablets []*TabletMetadata
 }
 
 // TabletMetadata holds metadata for single tablet
+// Experimental, this interface and use may change
 type TabletMetadata struct {
 	KeyspaceName string
 	TableId      UUID
@@ -151,6 +153,7 @@ type TabletMetadata struct {
 }
 
 // TabletMetadata holds metadata for single replica
+// Experimental, this interface and use may change
 type ReplicaMetadata struct {
 	HostId  UUID
 	ShardId int
@@ -245,6 +248,8 @@ type schemaDescriber struct {
 	mu      sync.Mutex
 
 	cache        map[string]*KeyspaceMetadata
+
+	// Experimental, this interface and use may change
 	tabletsCache *TabletsMetadata
 }
 
@@ -278,6 +283,7 @@ func (s *schemaDescriber) getSchema(keyspaceName string) (*KeyspaceMetadata, err
 	return metadata, nil
 }
 
+// Experimental, this interface and use may change
 func (s *schemaDescriber) getTabletsSchema() *TabletsMetadata {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -287,6 +293,7 @@ func (s *schemaDescriber) getTabletsSchema() *TabletsMetadata {
 	return metadata
 }
 
+// Experimental, this interface and use may change
 func (s *schemaDescriber) refreshTabletsSchema() {
 	tablets := s.session.getTablets()
 	s.tabletsCache.Tablets = []*TabletMetadata{}

policies.go

@@ -96,6 +96,7 @@ func (c *cowHostList) remove(ip net.IP) bool {
 }
 
 // cowTabletList implements a copy on write tablet list, its equivalent type is []*TabletInfo
+// Experimental, this interface and use may change
 type cowTabletList struct {
 	list atomic.Value
 	mu   sync.Mutex
@@ -306,6 +307,7 @@ type HostTierer interface {
 type HostSelectionPolicy interface {
 	HostStateNotifier
 	SetPartitioner
+	// Experimental, this interface and use may change
 	SetTablets
 	KeyspaceChanged(KeyspaceUpdateEvent)
 	Init(*Session)
@@ -357,9 +359,11 @@ type roundRobinHostPolicy struct {
 func (r *roundRobinHostPolicy) IsLocal(*HostInfo) bool              { return true }
 func (r *roundRobinHostPolicy) KeyspaceChanged(KeyspaceUpdateEvent) {}
 func (r *roundRobinHostPolicy) SetPartitioner(partitioner string)   {}
-func (r *roundRobinHostPolicy) SetTablets(tablets []*TabletInfo)    {}
 func (r *roundRobinHostPolicy) Init(*Session)                       {}
 
+// Experimental, this interface and use may change
+func (r *roundRobinHostPolicy) SetTablets(tablets []*TabletInfo) {}
+
 func (r *roundRobinHostPolicy) Pick(qry ExecutableQuery) NextHost {
 	nextStartOffset := atomic.AddUint64(&r.lastUsedHostIdx, 1)
 	return roundRobbin(int(nextStartOffset), r.hosts.get())
@@ -437,6 +441,7 @@ type tokenAwareHostPolicy struct {
 
 	logger StdLogger
 
+	// Experimental, this interface and use may change
 	tablets cowTabletList
 }
 
@@ -504,6 +509,7 @@ func (t *tokenAwareHostPolicy) SetPartitioner(partitioner string) {
 	}
 }
 
+// Experimental, this interface and use may change
 func (t *tokenAwareHostPolicy) SetTablets(tablets []*TabletInfo) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
@@ -630,27 +636,44 @@ func (t *tokenAwareHostPolicy) Pick(qry ExecutableQuery) NextHost {
 
 	var replicas []*HostInfo
 
-	t.tablets.mu.Lock()
-	tablets := t.tablets.get()
+	if qry.GetSession() != nil && qry.GetSession().cfg.experimentalTabletsEnabled {
+		t.tablets.mu.Lock()
+		tablets := t.tablets.get()
 
 	// Search for tablets with Keyspace and Table from the Query
 	l := findTablets(tablets, qry.Keyspace(), qry.Table())
 
-	if l != -1 {
-		tablet := findTabletForToken(tablets, token, l)
-
-		replicas = []*HostInfo{}
-		for _, replica := range tablet.Replicas() {
-			t.hosts.mu.Lock()
-			hosts := t.hosts.get()
-			for _, host := range hosts {
-				if host.hostId == replica.hostId.String() {
-					replicas = append(replicas, host)
-					break
+		if l != -1 {
+			tablet := findTabletForToken(tablets, token, l)
+
+			replicas = []*HostInfo{}
+			for _, replica := range tablet.Replicas() {
+				t.hosts.mu.Lock()
+				hosts := t.hosts.get()
+				for _, host := range hosts {
+					if host.hostId == replica.hostId.String() {
+						replicas = append(replicas, host)
+						break
+					}
 				}
+				t.hosts.mu.Unlock()
+			}
+		} else {
+			ht := meta.replicas[qry.Keyspace()].replicasFor(token)
+
+			if ht == nil {
+				host, _ := meta.tokenRing.GetHostForToken(token)
+				replicas = []*HostInfo{host}
+			} else {
+				replicas = ht.hosts
 			}
-			t.hosts.mu.Unlock()
 		}
+
+		if t.shuffleReplicas && !qry.IsLWT() {
+			replicas = shuffleHosts(replicas)
+		}
+
+		t.tablets.mu.Unlock()
 	} else {
 		ht := meta.replicas[qry.Keyspace()].replicasFor(token)
 
@@ -659,15 +682,12 @@ func (t *tokenAwareHostPolicy) Pick(qry ExecutableQuery) NextHost {
 			replicas = []*HostInfo{host}
 		} else {
 			replicas = ht.hosts
+			if t.shuffleReplicas && !qry.IsLWT() {
+				replicas = shuffleHosts(replicas)
+			}
 		}
 	}
 
-	if t.shuffleReplicas && !qry.IsLWT() {
-		replicas = shuffleHosts(replicas)
-	}
-
-	t.tablets.mu.Unlock()
-
 	var (
 		fallbackIter NextHost
 		i, j, k      int
@@ -775,9 +795,11 @@ type hostPoolHostPolicy struct {
 func (r *hostPoolHostPolicy) Init(*Session)                       {}
 func (r *hostPoolHostPolicy) KeyspaceChanged(KeyspaceUpdateEvent) {}
 func (r *hostPoolHostPolicy) SetPartitioner(string)               {}
-func (r *hostPoolHostPolicy) SetTablets(tablets []*TabletInfo)    {}
 func (r *hostPoolHostPolicy) IsLocal(*HostInfo) bool              { return true }
 
+// Experimental, this interface and use may change
+func (r *hostPoolHostPolicy) SetTablets(tablets []*TabletInfo) {}
+
 func (r *hostPoolHostPolicy) SetHosts(hosts []*HostInfo) {
 	peers := make([]string, len(hosts))
 	hostMap := make(map[string]*HostInfo, len(hosts))
@@ -912,12 +934,13 @@ func DCAwareRoundRobinPolicy(localDC string) HostSelectionPolicy {
 func (d *dcAwareRR) Init(*Session)                       {}
 func (d *dcAwareRR) KeyspaceChanged(KeyspaceUpdateEvent) {}
 func (d *dcAwareRR) SetPartitioner(p string)             {}
-func (d *dcAwareRR) SetTablets(tablets []*TabletInfo)    {}
-
 func (d *dcAwareRR) IsLocal(host *HostInfo) bool {
 	return host.DataCenter() == d.local
 }
 
+// Experimental, this interface and use may change
+func (d *dcAwareRR) SetTablets(tablets []*TabletInfo) {}
+
 func (d *dcAwareRR) AddHost(host *HostInfo) {
 	if d.IsLocal(host) {
 		d.localHosts.add(host)
@@ -1006,12 +1029,13 @@ func RackAwareRoundRobinPolicy(localDC string, localRack string) HostSelectionPo
 func (d *rackAwareRR) Init(*Session)                       {}
 func (d *rackAwareRR) KeyspaceChanged(KeyspaceUpdateEvent) {}
 func (d *rackAwareRR) SetPartitioner(p string)             {}
-func (d *rackAwareRR) SetTablets(tablets []*TabletInfo)    {}
-
 func (d *rackAwareRR) MaxHostTier() uint {
 	return 2
 }
 
+// Experimental, this interface and use may change
+func (d *rackAwareRR) SetTablets(tablets []*TabletInfo) {}
+
 func (d *rackAwareRR) HostTier(host *HostInfo) uint {
 	if host.DataCenter() == d.localDC {
 		if host.Rack() == d.localRack {

query_executor.go

@@ -23,6 +23,8 @@ type ExecutableQuery interface {
 	withContext(context.Context) ExecutableQuery
 
 	RetryableQuery
+
+	GetSession() *Session
 }
 
 type queryExecutor struct {

ring.go

@@ -22,6 +22,7 @@ type ring struct {
 	hostList []*HostInfo
 	pos      uint32
 
+	// Experimental, this interface and use may change
 	tabletList []*TabletInfo
 
 	// TODO: we should store the ring metadata here also.
@@ -144,6 +145,7 @@ func (c *clusterMetadata) setPartitioner(partitioner string) {
 	}
 }
 
+// Experimental, this interface and use may change
 func (r *ring) setTablets(newTablets []*TabletInfo) {
 	r.mu.Lock()
 	defer r.mu.Unlock()

scylla.go

@@ -333,22 +333,24 @@ func (p *scyllaConnPicker) Pick(t token, keyspace string, table string) *Conn {
 		return nil
 	}
 
-	tablets := p.conns[0].session.getTablets()
-
 	idx := -1
 
-	// Search for tablets with Keyspace and Table from the Query
-	l := findTablets(tablets, keyspace, table)
+	if p.conns[0].session.cfg.experimentalTabletsEnabled {
+		tablets := p.conns[0].session.getTablets()
+
+		// Search for tablets with Keyspace and Table from the Query
+		l := findTablets(tablets, keyspace, table)
 
-	if l != -1 {
-		tablet := findTabletForToken(tablets, mmt, l)
+		if l != -1 {
+			tablet := findTabletForToken(tablets, mmt, l)
 
-		for _, replica := range tablet.replicas {
-			if replica.hostId.String() == p.hostId {
-				idx = replica.shardId
+			for _, replica := range tablet.replicas {
+				if replica.hostId.String() == p.hostId {
+					idx = replica.shardId
+				}
 			}
 		}
-	} 
+	}
 	if idx == -1 {
 		idx = p.shardOf(mmt)
 	}