Docs
menu Home Community Trace Viewer GitHub

Trace Processor (C++)

Trace Processor is a C++ library (src/trace_processor) that ingests traces in a variety of formats and exposes an SQL interface for querying them through a consistent set of tables. It also computes trace summaries, annotates traces with human-readable descriptions, and derives new events from trace contents.

Trace processor block diagram

Most users interact with Trace Processor through the trace_processor shell, a command-line wrapper around the library that opens an interactive PerfettoSQL prompt. To embed Trace Processor in another C++ application, see Embedding the C++ library. Python users should use the Python API instead.

The trace_processor shell

The trace_processor shell is a command-line binary that loads a trace and opens an interactive SQL prompt on it.

Downloading the shell

The shell is a thin Python wrapper that you download from the Perfetto website. On first use it fetches and caches the native binary for your platform (including trace_processor_shell.exe on Windows) under ~/.local/share/perfetto/prebuilts.

curl -LO https://get.perfetto.dev/trace_processor chmod +x ./trace_processor

curl.exe -LO https://get.perfetto.dev/trace_processor

Python 3 is required to run the wrapper script. curl ships with Windows 10 and later.

Running the shell

Once downloaded, run it on a trace file:

./trace_processor trace.perfetto-trace

python trace_processor trace.perfetto-trace

This opens an interactive SQL shell where you can query the trace. For how to write queries, see the Getting Started with PerfettoSQL guide.

TIP: the trace file can also be a ZIP or TAR archive containing several traces: they are merged onto a single timeline. See Merging traces from the command line.

For example, to see all the slices in a trace:

> SELECT ts, dur, name FROM slice LIMIT 10; ts dur name -------------------- -------------------- --------------------------- 261187017446933 358594 eglSwapBuffersWithDamageKHR 261187017518340 357 onMessageReceived 261187020825163 9948 queueBuffer 261187021345235 642 bufferLoad 261187121345235 153 query ...

Or, to see the values of all counters:

> SELECT ts, value FROM counter LIMIT 10; ts value -------------------- -------------------- 261187012149954 1454.000000 261187012399172 4232.000000 261187012447402 14304.000000 261187012535839 15490.000000 261187012590890 17490.000000 261187012590890 16590.000000 ...

Keeping a trace warm: sessions

Parsing a large trace takes time. If you plan to run several queries against the same trace, load it once into a named background session and point each invocation at that session:

# Load the trace once into a background session. trace_processor server unix --name mysession --daemonize trace.pftrace # Run queries against the warm session instead of re-loading the trace. trace_processor query --remote mysession "SELECT count(*) FROM slice"

The query, interactive, metrics and summarize subcommands all accept --remote, which talks to a session over the same TraceProcessor RPC interface the Perfetto UI uses. See Analyzing traces from the command line for a walkthrough, and the server subcommand below for the mode and flag details.

Subcommand interface

Besides the interactive REPL, trace_processor takes a subcommand as its first argument for non-interactive workflows:

trace_processor <command> [flags] [positional args]

trace_processor --help prints the top-level summary below. To see the flags of one subcommand, run trace_processor <command> --help (equivalently trace_processor help <command>):

Perfetto Trace Processor. Usage: trace_processor [command] [flags] [trace_file] If no command is given, opens an interactive SQL shell on the trace file. Commands: query Load a trace and run a SQL query. interactive Interactive SQL shell (default if no command is given). server Start an RPC server. summarize Compute a trace summary from specs and/or built-in metrics. export Export trace data (sqlite, arrow_tar, perfetto). metrics Run v1 metrics (deprecated; use 'summarize --metrics-v2'). convert Convert trace format. Common flags (apply to all commands): -h, --help Show help (per-command if after a command). -v, --version Print version. --full-sort Force full sort ignoring windowing. --no-ftrace-raw Prevent ingestion of typed ftrace into raw table. --add-sql-package PATH Register SQL files from a directory as a package. -m, --metatrace FILE Enable metatracing, write to FILE.

Backwards compatibility. The classic flat-flag interface (-q, -Q, --httpd, --summary, --run-metrics, -e, --stdiod) is still supported through an internal translation layer, so existing scripts keep working unchanged. Run trace_processor --help-classic for the full list of classic flags.

query: run SQL

query loads a trace, runs one or more ;-separated SQL statements, prints the results to stdout, and exits. SQL can be passed as an argument, read from a file, or piped on stdin:

# Pass SQL as an argument. trace_processor query trace.pftrace "SELECT ts, dur, name FROM slice LIMIT 5" # Read SQL from a file. trace_processor query -f queries.sql trace.pftrace # Pipe SQL on stdin. cat queries.sql | trace_processor query trace.pftrace

Each statement's result set is printed as CSV, and consecutive result sets are separated by a single blank line. The separator is unambiguous because every string value is quoted.

Flags:

interactive: REPL

interactive opens the same interactive PerfettoSQL prompt shown in the previous section. It is the default subcommand, so trace_processor trace.pftrace and trace_processor interactive trace.pftrace are equivalent. The only subcommand-specific flag is -W, --wide.

server: HTTP, stdio, or unix RPC

server exposes trace processor over a remote-procedure-call protocol:

# HTTP server, used by ui.perfetto.dev. Listens on port 9001 by default. trace_processor server http # Pre-load a trace and serve it over HTTP. trace_processor server http trace.pftrace # stdio server: length-prefixed RPC for tooling that embeds # trace_processor as a subprocess. trace_processor server stdio # Named unix-socket session: keeps the trace warm for repeated # `query --remote <name>` calls (see the sessions section above). trace_processor server unix --name mysession --daemonize trace.pftrace # Stop a unix session by name or socket path. trace_processor server kill mysession

Flags:

The trace file is optional in http and unix modes; clients can also load traces remotely. The most common client is the Perfetto UI, which auto-detects a local server and offloads trace parsing to it. See Visualising large traces for the end-user flow, or trace_processor.proto for the RPC wire schema.

summarize: compute trace summaries

summarize computes a trace summary. Pass the trace file first, then any spec files; select built-in v2 metrics with --metrics-v2:

# Run every available v2 metric. trace_processor summarize --metrics-v2 all trace.pftrace # Run two specific metrics defined in spec.textproto. trace_processor summarize \ --metrics-v2 startup_metric,memory_metric \ trace.pftrace spec.textproto

Flags:

Spec files are detected as binary or text by extension (.pb for binary, .textproto for text), with content sniffing as a fallback.

export: write trace data to a file

export writes the parsed trace data to a file. The format is the first positional argument, the output path is given with -o:

# Version-coupled archive, loadable by the same version of trace processor. trace_processor export perfetto -o archive.tar trace.pftrace # Static tables as standard Arrow files in a tar. trace_processor export arrow_tar -o tables.tar trace.pftrace # Static tables and views as a SQLite database. trace_processor export sqlite -o trace.db trace.pftrace

Formats:

Flags:

All three formats export the statically registered tables; only sqlite also includes views. Runtime tables created during the session (e.g. CREATE PERFETTO TABLE) are not exported. Exports stream to disk, so memory use stays bounded for large traces. For task-oriented recipes, see Export trace data.

Global flags (apply to every subcommand)

These flags are accepted in addition to the subcommand-specific flags above and behave the same across all subcommands:

Embedding the C++ library

The public API centers on the TraceProcessor class in trace_processor.h. All high-level operations (parsing trace bytes, executing SQL queries, computing summaries) are member functions of this class.

Create an instance with CreateInstance:

#include "perfetto/trace_processor/trace_processor.h" using namespace perfetto::trace_processor; Config config; std::unique_ptr<TraceProcessor> tp = TraceProcessor::CreateInstance(config);

Loading a trace

To ingest a trace, call Parse repeatedly with chunks of trace bytes, then NotifyEndOfFile once the whole trace has been pushed:

while (/* more data available */) { TraceBlobView blob = /* ... */; base::Status status = tp->Parse(std::move(blob)); if (!status.ok()) { /* handle error */ } } base::Status status = tp->NotifyEndOfFile();

Because reading a trace from the filesystem is a common case, a helper ReadTrace is provided in read_trace.h:

#include "perfetto/trace_processor/read_trace.h" base::Status status = ReadTrace(tp.get(), "/path/to/trace.pftrace");

ReadTrace reads the file from disk, calls Parse with the contents, and calls NotifyEndOfFile for you.

Executing queries

Run queries with ExecuteQuery, which returns an Iterator that streams rows back to the caller:

auto it = tp->ExecuteQuery("SELECT ts, name FROM slice LIMIT 10"); while (it.Next()) { int64_t ts = it.Get(0).AsLong(); std::string name = it.Get(1).AsString(); // ... } if (!it.Status().ok()) { // Query produced an error. }

Two important rules when using the iterator:

See the comments in iterator.h for the full iterator API.

Other functionality

The TraceProcessor class also exposes:

Refer to the comments in trace_processor.h for the complete API surface.