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feat(spanner): add DCP DirectPath fallback #14612

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cc0e058
feat(spanner): add dynamic channel pool
rahul2393 May 19, 2026
63cac5e
feat(spanner): add DCP DirectPath fallback
rahul2393 May 19, 2026
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2 changes: 1 addition & 1 deletion spanner/batch.go
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Original file line number Diff line number Diff line change
Expand Up @@ -370,7 +370,7 @@ func (t *BatchReadOnlyTransaction) Execute(ctx context.Context, p *Partition) *R
nil,
t.setTimestamp,
t.release,
asGRPCSpannerClient(client),
requestIDHeaderProviderFromSpannerClient(client),
true,
false,
)
Expand Down
103 changes: 71 additions & 32 deletions spanner/client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,12 @@ const (

// MinSessions for Experimental Host connection
experimentalHostMinSessions = 0

// DirectPath fallback policy used by both non-DCP grpc-gcp fallback and the
// DCP DirectPath/CloudPath wrapper.
directPathFallbackErrorRateThreshold = float32(1)
directPathFallbackMinFailedCalls = 1
directPathFallbackPeriod = time.Minute * 3
)

const (
Expand Down Expand Up @@ -285,6 +291,9 @@ type ClientConfig struct {
// SessionPoolConfig is the configuration for session pool.
SessionPoolConfig

// DynamicChannelPoolConfig is the opt-in configuration for dynamic gRPC channel pooling.
DynamicChannelPoolConfig DynamicChannelPoolConfig

// SessionLabels for the sessions created by this client.
// See https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#session
// for more info.
Expand Down Expand Up @@ -527,14 +536,69 @@ func newClientWithConfig(ctx context.Context, database string, config ClientConf

var pool gtransport.ConnPool
var endpointClientOpts []option.ClientOption
var sc *sessionClient

isFallbackEnabled := true
if val, ok := os.LookupEnv("GOOGLE_SPANNER_ENABLE_GCP_FALLBACK"); ok {
if b, err := strconv.ParseBool(val); err == nil {
isFallbackEnabled = b
}
}
if gme != nil {

// TODO(loite): Remove as the original map cannot be changed by the user
// anyways, and the client library is also not changing it.
// Make a copy of labels.
sessionLabels := make(map[string]string)
for k, v := range config.SessionLabels {
sessionLabels[k] = v
}

md := metadata.Pairs(resourcePrefixHeader, database)
if config.Compression == gzip.Name {
md.Append(requestsCompressionHeader, gzip.Name)
}
// Append end to end tracing header if SPANNER_ENABLE_END_TO_END_TRACING
// environment variable has been set or client has passed the opt-in
// option in ClientConfig.
endToEndTracingEnvironmentVariable := os.Getenv("SPANNER_ENABLE_END_TO_END_TRACING")
if config.EnableEndToEndTracing || endToEndTracingEnvironmentVariable == "true" {
md.Append(endToEndTracingHeader, "true")
}

if isAFEBuiltInMetricEnabled {
md.Append(afeMetricHeader, "true")
}
if config.BatchTimeout == 0 {
config.BatchTimeout = time.Minute
}

dcpEnabled := config.DynamicChannelPoolConfig.DCPEnabled && gme == nil && !isExperimentalLocationAPIEnabledForConfig(config) && os.Getenv("SPANNER_EMULATOR_HOST") == ""
if dcpEnabled {
reqIDInjector := new(requestIDHeaderInjector)
dcpOpts := append([]option.ClientOption{}, opts...)
dcpOpts = append(dcpOpts,
option.WithGRPCDialOption(grpc.WithChainStreamInterceptor(reqIDInjector.interceptStream)),
option.WithGRPCDialOption(grpc.WithChainUnaryInterceptor(reqIDInjector.interceptUnary)),
)
sc = newSessionClient(nil, database, config.UserAgent, sessionLabels, config.DatabaseRole, config.DisableRouteToLeader, md, config.BatchTimeout, config.Logger, config.CallOptions)
sc.metricsTracerFactory = metricsTracerFactory
dial := func(dialCtx context.Context) (gtransport.ConnPool, error) {
return gtransport.DialPool(dialCtx, allClientOpts(1, config.Compression, config.EnableDirectAccess, dcpOpts...)...)
}
var fallbackDial func(context.Context) (gtransport.ConnPool, error)
if isFallbackEnabled && isDirectPathEnabled {
fallbackDial = func(dialCtx context.Context) (gtransport.ConnPool, error) {
return gtransport.DialPool(dialCtx, append(allClientOpts(1, config.Compression, config.EnableDirectAccess, dcpOpts...), internaloption.EnableDirectPath(false))...)
}
}
dcp, err := newDynamicChannelPool(ctx, sc, config.DynamicChannelPoolConfig, 0, dial, fallbackDial)
if err != nil {
return nil, err
}
pool = dcp
sc.connPool = pool
sc.dynamicPool = dcp
} else if gme != nil {
// Use GCPMultiEndpoint if provided.
pool = &gmeWrapper{gme}
endpointClientOpts = append(endpointClientOpts, opts...)
Expand Down Expand Up @@ -568,9 +632,9 @@ func newClientWithConfig(ctx context.Context, database string, config ClientConf

fbOpts := grpcgcp.NewGCPFallbackOptions()
fbOpts.EnableFallback = true
fbOpts.ErrorRateThreshold = 1
fbOpts.MinFailedCalls = 1
fbOpts.Period = time.Minute * 3
fbOpts.ErrorRateThreshold = directPathFallbackErrorRateThreshold
fbOpts.MinFailedCalls = directPathFallbackMinFailedCalls
fbOpts.Period = directPathFallbackPeriod

if metricsTracerFactory != nil && metricsTracerFactory.meterProvider != nil {
fbOpts.MeterProvider = metricsTracerFactory.meterProvider
Expand Down Expand Up @@ -608,45 +672,20 @@ func newClientWithConfig(ctx context.Context, database string, config ClientConf
}
}

// TODO(loite): Remove as the original map cannot be changed by the user
// anyways, and the client library is also not changing it.
// Make a copy of labels.
sessionLabels := make(map[string]string)
for k, v := range config.SessionLabels {
sessionLabels[k] = v
}

// Default configs for session pool.
if config.MaxOpened == 0 {
config.MaxOpened = uint64(pool.Num() * 100)
}
if config.MaxBurst == 0 {
config.MaxBurst = DefaultSessionPoolConfig.MaxBurst
}
if config.BatchTimeout == 0 {
config.BatchTimeout = time.Minute
}

md := metadata.Pairs(resourcePrefixHeader, database)
if config.Compression == gzip.Name {
md.Append(requestsCompressionHeader, gzip.Name)
}
// Append end to end tracing header if SPANNER_ENABLE_END_TO_END_TRACING
// environment variable has been set or client has passed the opt-in
// option in ClientConfig.
endToEndTracingEnvironmentVariable := os.Getenv("SPANNER_ENABLE_END_TO_END_TRACING")
if config.EnableEndToEndTracing || endToEndTracingEnvironmentVariable == "true" {
md.Append(endToEndTracingHeader, "true")
}

if isAFEBuiltInMetricEnabled {
md.Append(afeMetricHeader, "true")
}

// Multiplexed sessions are always enabled as the session pool has been removed.

// Create a session client.
sc := newSessionClient(pool, database, config.UserAgent, sessionLabels, config.DatabaseRole, config.DisableRouteToLeader, md, config.BatchTimeout, config.Logger, config.CallOptions)
if sc == nil {
sc = newSessionClient(pool, database, config.UserAgent, sessionLabels, config.DatabaseRole, config.DisableRouteToLeader, md, config.BatchTimeout, config.Logger, config.CallOptions)
}

// Create an OpenTelemetry configuration
otConfig, err := createOpenTelemetryConfig(ctx, config.OpenTelemetryMeterProvider, config.Logger, sc.id, database)
Expand Down
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