grpc/doc/trace_flags.md

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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.
  - cronet - Cronet transport engine.
  - 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.
  - executor - gRPC's legacy thread pool ('the executor').
  - 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.
  - stateful_session_filter - Stateful session affinity.
  - subchannel - Connectivity state of subchannels.
  - 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.
  - 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.
  - ph2 - 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.

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