gRPC Trace Flags

The GRPC_TRACE environment variable supports a comma-separated list of tracer names or glob patterns that provide additional insight into how gRPC C core is processing requests via debug logs. Available tracers include:

• api - API calls to the C core.
• backend_metric - C++ backend metric recorder APIs.
• backend_metric_filter - Filter that populates backend metric data in server trailing metadata.
• bdp_estimator - Behavior of bdp estimation logic.
• call - Traces operations on a call through the gRPC stack.
• call_error - Possible errors contributing to final call statuses.
• cares_address_sorting - Operations of the c-ares based DNS resolver's address sorter.
• cares_resolver - Operations of the c-ares based DNS resolver.
• cds_lb - CDS LB policy.
• channel - Operations on the C core channel stack.
• channel_stack - Construction of the set of filters in a channel stack.
• chaotic_good - Chaotic good transport.
• chttp2_hpack_parser - HTTP/2 HPACK parser.
• chttp2_new_stream - HTTP/2 incoming stream creation.
• client_channel - Client channel control plane activity, including resolver and load balancing policy interaction.
• client_channel_call - Client channel call activity related to name resolution.
• client_channel_lb_call - Client channel call activity related to load balancing picking.
• client_idle_filter - Client idleness filter.
• compression - Compression operations.
• connectivity_state - Connectivity state changes to channels.
• dns_resolver - The active DNS resolver.
• environment_autodetect - GCP environment auto-detection.
• event_engine - High-level EventEngine operations.
• event_engine_client_channel_resolver - EventEngine-based client channel resolver state and events.
• event_engine_dns - EventEngine DNS resolver.
• event_engine_endpoint - EventEngine Endpoint operations.
• event_engine_endpoint_data - Detailed dump of EventEngine endpoint TCP data.
• event_engine_poller - EventEngine Poller events.
• fault_injection_filter - Fault injection.
• flowctl - Http2 flow control.
• fork - Fork support.
• glb - gRPClb load balancer.
• grpc_authz_api - gRPC authorization.
• handshaker - Handshaking state.
• health_check_client - Health checking client code.
• http - Http2 transport engine.
• http1 - HTTP/1.x operations performed by gRPC.
• http2_ping - Pings/ping acks/antagonist writes in http2 stack.
• http2_stream_state - Http2 stream state mutations.
• http_keepalive - gRPC keepalive pings.
• inproc - In-process transport.
• metadata_query - GCP metadata queries.
• op_failure - Error information when failure is pushed onto a completion queue. The api tracer must be enabled for this flag to have any effect.
• orca_client - Out-of-band backend metric reporting client.
• outlier_detection_lb - Outlier detection.
• pick_first - Pick first load balancing policy.
• plugin_credentials - Plugin credentials.
• priority_lb - Priority LB policy.
• queue_pluck - Completion queue plucking. The api tracer must be enabled for this flag to have any effect.
• resource_quota - Resource quota objects internals.
• retry - Call retries.
• ring_hash_lb - Ring hash load balancing policy.
• rls_lb - RLS load balancing policy.
• round_robin - Round robin load balancing policy.
• secure_endpoint - Bytes flowing through encrypted channels.
• server_channel - Lightweight trace of significant server channel events.
• server_config_selector_interceptor - Traces calls in the server config selector interceptor.
• stateful_session_filter - Stateful session affinity.
• subchannel - Connectivity state of subchannels.
• subchannel_call - Call handling in the subchannel.
• subchannel_pool - Subchannel pool.
• tcp - Bytes in and out of a channel.
• timer - Timers (alarms) in the grpc internals.
• timer_check - more detailed trace of timer logic in grpc internals.
• token_fetcher_credentials - Token fetcher call credentials framework, used for (e.g.) oauth2 token fetcher credentials.
• tsi - TSI transport security.
• weighted_round_robin_lb - Weighted round robin load balancing policy.
• weighted_target_lb - Weighted target LB policy.
• xds_client - XDS client.
• xds_client_refcount - Refcount of XDS client.
• xds_cluster_impl_lb - XDS Cluster impl LB policy.
• xds_cluster_manager_lb - XDS Cluster manager LB policy.
• xds_override_host_lb - XDS Override host LB.
• xds_resolver - XDS Resolver.
• xds_server_config_fetcher - XDS Server config fetcher.
• xds_wrr_locality_lb - XDS WRR locality LB policy.

The following tracers will only run in binaries built in DEBUG mode. This is accomplished by invoking bazel build --config=dbg <target>

• auth_context_refcount - Auth context refcounting.
• call_combiner - Call combiner state.
• call_refcount - Refcount on call.
• call_state - Traces transitions through the call spine state machine.
• chttp2_server_refcount - Refcounting in Chttp2 Server.
• closure - Legacy closure creation, scheduling, and completion.
• combiner - Combiner lock state.
• cq_refcount - Completion queue refcounting.
• error_refcount - Error refcounting.
• fd_refcount - File descriptor refcounting.
• fd_trace - Legacy file descriptor create(), shutdown() and close() calls for channel fds.
• lb_policy_refcount - LB policy refcounting.
• party_state - Coordination of activities related to a call.
• pending_tags - Still-in-progress tags on completion queues. The api tracer must be enabled for this flag to have any effect.
• http2_ph2_transport - Promise Based HTTP2 transport.
• polling - The active polling engine.
• polling_api - API calls to polling engine.
• promise_primitives - Low-level primitives in the promise library.
• resolver_refcount - Resolver refcouting.
• security_connector_refcount - Refcounting for security connectors (part of channel credentials).
• slice_refcount - Slice refcounting.
• stream_refcount - Stream refcounting.
• subchannel_refcount - Subchannel refcounting.
• work_serializer - A synchronization mechanism used to ensure that only one thread is executing at a given time.
• ztrace - Trace ztrace appends globally (for debugging the ztrace system itself).

Glob patterns and special cases:

• * can be used to turn all traces on.
• Individual traces can be disabled by prefixing them with -.
• *refcount* will turn on all of the tracers for refcount debugging.
• if list_tracers is present, then all of the available tracers will be printed when the program starts up.

Example: export GRPC_TRACE=*,-pending_tags