CASSGO-23 Make Session immutable

Patch by Stanislav Bychkov; reviewed by João Reis for CASSGO-23

Author: ribaraka

CHANGELOG.md

@@ -54,6 +54,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Move "execute batch" methods to Batch type (CASSGO-57)
 
+- Make `Session` immutable by removing setters and associated mutex (CASSGO-23)
+
 ### Fixed
 - Cassandra version unmarshal fix (CASSGO-49)
 

cassandra_test.go

@@ -152,11 +152,10 @@ func TestTracing(t *testing.T) {
 	}
 
 	// also works from session tracer
-	session.SetTrace(trace)
 	trace.mu.Lock()
 	buf.Reset()
 	trace.mu.Unlock()
-	if err := session.Query(`SELECT id FROM trace WHERE id = ?`, 42).Scan(&value); err != nil {
+	if err := session.Query(`SELECT id FROM trace WHERE id = ?`, 42).Trace(trace).Scan(&value); err != nil {
 		t.Fatal("select:", err)
 	}
 	if buf.Len() == 0 {

cluster.go

@@ -263,6 +263,17 @@ type ClusterConfig struct {
 	// If not specified, defaults to the gocql.defaultLogger.
 	Logger StdLogger
 
+	// Tracer will be used for all queries. Alternatively it can be set of on a
+	// per query basis.
+	// default: nil
+	Tracer Tracer
+
+	// NextPagePrefetch sets the default threshold for pre-fetching new pages. If
+	// there are only p*pageSize rows remaining, the next page will be requested
+	// automatically. This value can also be changed on a per-query basis.
+	// default: 0.25.
+	NextPagePrefetch float64
+
 	// internal config for testing
 	disableControlConn bool
 }
@@ -298,6 +309,7 @@ func NewCluster(hosts ...string) *ClusterConfig {
 		ConvictionPolicy:       &SimpleConvictionPolicy{},
 		ReconnectionPolicy:     &ConstantReconnectionPolicy{MaxRetries: 3, Interval: 1 * time.Second},
 		WriteCoalesceWaitTime:  200 * time.Microsecond,
+		NextPagePrefetch:       0.25,
 	}
 	return cfg
 }

doc.go

@@ -271,7 +271,7 @@
 //
 // # Paging
 //
-// The driver supports paging of results with automatic prefetch, see ClusterConfig.PageSize, Session.SetPrefetch,
+// The driver supports paging of results with automatic prefetch, see ClusterConfig.PageSize,
 // Query.PageSize, and Query.Prefetch.
 //
 // It is also possible to control the paging manually with Query.PageState (this disables automatic prefetch).

session.go

@@ -75,8 +75,6 @@ type Session struct {
 	ring     ring
 	metadata clusterMetadata
 
-	mu sync.RWMutex
-
 	control *controlConn
 
 	// event handlers
@@ -153,14 +151,15 @@ func NewSession(cfg ClusterConfig) (*Session, error) {
 
 	s := &Session{
 		cons:            cfg.Consistency,
-		prefetch:        0.25,
+		prefetch:        cfg.NextPagePrefetch,
 		cfg:             cfg,
 		pageSize:        cfg.PageSize,
 		stmtsLRU:        &preparedLRU{lru: lru.New(cfg.MaxPreparedStmts)},
 		connectObserver: cfg.ConnectObserver,
 		ctx:             ctx,
 		cancel:          cancel,
 		logger:          cfg.logger(),
+		trace:           cfg.Tracer,
 	}
 
 	s.schemaDescriber = newSchemaDescriber(s)
@@ -416,41 +415,6 @@ func (s *Session) reconnectDownedHosts(intv time.Duration) {
 	}
 }
 
-// SetConsistency sets the default consistency level for this session. This
-// setting can also be changed on a per-query basis and the default value
-// is Quorum.
-func (s *Session) SetConsistency(cons Consistency) {
-	s.mu.Lock()
-	s.cons = cons
-	s.mu.Unlock()
-}
-
-// SetPageSize sets the default page size for this session. A value <= 0 will
-// disable paging. This setting can also be changed on a per-query basis.
-func (s *Session) SetPageSize(n int) {
-	s.mu.Lock()
-	s.pageSize = n
-	s.mu.Unlock()
-}
-
-// SetPrefetch sets the default threshold for pre-fetching new pages. If
-// there are only p*pageSize rows remaining, the next page will be requested
-// automatically. This value can also be changed on a per-query basis and
-// the default value is 0.25.
-func (s *Session) SetPrefetch(p float64) {
-	s.mu.Lock()
-	s.prefetch = p
-	s.mu.Unlock()
-}
-
-// SetTrace sets the default tracer for this session. This setting can also
-// be changed on a per-query basis.
-func (s *Session) SetTrace(trace Tracer) {
-	s.mu.Lock()
-	s.trace = trace
-	s.mu.Unlock()
-}
-
 // Query generates a new query object for interacting with the database.
 // Further details of the query may be tweaked using the resulting query
 // value before the query is executed. Query is automatically prepared
@@ -1005,7 +969,6 @@ type queryRoutingInfo struct {
 func (q *Query) defaultsFromSession() {
 	s := q.session
 
-	s.mu.RLock()
 	q.cons = s.cons
 	q.pageSize = s.pageSize
 	q.trace = s.trace
@@ -1018,7 +981,6 @@ func (q *Query) defaultsFromSession() {
 	q.metrics = &queryMetrics{m: make(map[string]*hostMetrics)}
 
 	q.spec = &NonSpeculativeExecution{}
-	s.mu.RUnlock()
 }
 
 // Statement returns the statement that was used to generate this query.
@@ -1855,7 +1817,6 @@ func (s *Session) NewBatch(typ BatchType) *Batch {
 
 // Batch creates a new batch operation using defaults defined in the cluster
 func (s *Session) Batch(typ BatchType) *Batch {
-	s.mu.RLock()
 	batch := &Batch{
 		Type:             typ,
 		rt:               s.cfg.RetryPolicy,
@@ -1871,7 +1832,6 @@ func (s *Session) Batch(typ BatchType) *Batch {
 		routingInfo:      &queryRoutingInfo{},
 	}
 
-	s.mu.RUnlock()
 	return batch
 }
 

session_test.go

@@ -35,43 +35,21 @@ import (
 )
 
 func TestSessionAPI(t *testing.T) {
-	cfg := &ClusterConfig{}
+	cfg := NewCluster()
 
 	s := &Session{
 		cfg:    *cfg,
 		cons:   Quorum,
 		policy: RoundRobinHostPolicy(),
 		logger: cfg.logger(),
 	}
+	defer s.Close()
 
 	s.pool = cfg.PoolConfig.buildPool(s)
 	s.executor = &queryExecutor{
 		pool:   s.pool,
 		policy: s.policy,
 	}
-	defer s.Close()
-
-	s.SetConsistency(All)
-	if s.cons != All {
-		t.Fatalf("expected consistency 'All', got '%v'", s.cons)
-	}
-
-	s.SetPageSize(100)
-	if s.pageSize != 100 {
-		t.Fatalf("expected pageSize 100, got %v", s.pageSize)
-	}
-
-	s.SetPrefetch(0.75)
-	if s.prefetch != 0.75 {
-		t.Fatalf("expceted prefetch 0.75, got %v", s.prefetch)
-	}
-
-	trace := &traceWriter{}
-
-	s.SetTrace(trace)
-	if s.trace != trace {
-		t.Fatalf("expected traceWriter '%v',got '%v'", trace, s.trace)
-	}
 
 	qry := s.Query("test", 1)
 	if v, ok := qry.values[0].(int); !ok {