docs/analysis/trace-processor-python.md

# Trace Processor (Python)

The trace processor Python API is built on the trace procesor
[C++ library](/docs/analysis/trace-processor.md). By integrating with Python,
the library allows using Python's rich data analysis ecosystem to process
traces.

## Setup

```
pip install perfetto
```

NOTE: The API is only compatible with Python3.

The main entry point to the API is the `TraceProcessor` class.

## Example Usage

The following examples demonstrate basic usage of the Python API.

### Querying Slices

This example shows how to query for slices and print their names.

```python
from perfetto.trace_processor import TraceProcessor
tp = TraceProcessor(trace='trace.perfetto-trace')

qr_it = tp.query('SELECT name FROM slice')
for row in qr_it:
  print(row.name)
```

**Output**

```
eglSwapBuffersWithDamageKHR
onMessageReceived
queueBuffer
bufferLoad
query
...
```

### Querying as a Pandas DataFrame

For more advanced analysis, you can convert query results to a Pandas DataFrame.

```python
from perfetto.trace_processor import TraceProcessor
tp = TraceProcessor(trace='trace.perfetto-trace')

qr_it = tp.query('SELECT ts, name FROM slice')
qr_df = qr_it.as_pandas_dataframe()
print(qr_df.to_string())
```

**Output**

```
ts                   name
-------------------- ---------------------------
     261187017446933 eglSwapBuffersWithDamageKHR
     261187017518340 onMessageReceived
     261187020825163 queueBuffer
     261187021345235 bufferLoad
     261187121345235 query
     ...
```

## Initialization

`TraceProcessor` can be initialized in a few ways depending on where the trace
is and whether you want to connect to an existing `trace_processor` instance or
start a new one.

**1. With a trace file or object (starts a new `trace_processor` instance):**

This is the most common use case. You can provide a trace in several ways:

- A path to a trace file: `TraceProcessor(trace='trace.perfetto-trace')`
- A file-like object (e.g., `io.BytesIO`): `TraceProcessor(trace=file_obj)`
- A generator yielding bytes: `TraceProcessor(trace=byte_generator)`
- A trace URI: `TraceProcessor(trace='resolver_name:key=value')`

```python
from perfetto.trace_processor import TraceProcessor

# Initialise TraceProcessor with a trace file path
tp = TraceProcessor(trace='trace.perfetto-trace')
```

**2. Connecting to a running `trace_processor` instance:**

If you have a `trace_processor` instance already running (e.g. started from the
command line), you can connect to it by providing its address.

```python
# Connect to a running instance
tp = TraceProcessor(addr='localhost:9001')

# Connect to a running instance and load a new trace into it
tp = TraceProcessor(trace='trace.perfetto-trace', addr='localhost:9001')
```

### Configuration

The `TraceProcessor` can be customized using the `TraceProcessorConfig` class.

```python
from perfetto.trace_processor import TraceProcessor, TraceProcessorConfig

config = TraceProcessorConfig(
    bin_path='/path/to/trace_processor', # Path to custom binary
    verbose=True,
    add_sql_packages=['/path/to/my/sql/modules']
)
tp = TraceProcessor(trace='trace.perfetto-trace', config=config)
```

`TraceProcessorConfig` has many options for customizing the `trace_processor`
instance. The most important are:

- `add_sql_packages`: A list of paths to additional PerfettoSQL packages to
  load. All SQL modules inside these packages will be available to include using
  `INCLUDE PERFETTO MODULE` PerfettoSQL statements.
- `verbose`: If `True`, `trace_processor` will print verbose output to stdout.
  This is useful for debugging and seeing more detailed error messages.
- `bin_path`: Path to the `trace_processor` binary. If not given, the latest
  prebuilt version will be downloaded.

## API

The `TraceProcessor` class provides various functions to interact with the
loaded trace.

### Query

The `query()` function takes an SQL query as input and returns an iterator over
the result rows. For more information on how to write queries, see the
[Getting Started with PerfettoSQL](perfetto-sql-getting-started.md) guide.

```python
from perfetto.trace_processor import TraceProcessor
tp = TraceProcessor(trace='trace.perfetto-trace')

qr_it = tp.query('SELECT ts, dur, name FROM slice')
for row in qr_it:
  print(row.ts, row.dur, row.name)
```

**Output**

```
261187017446933 358594 eglSwapBuffersWithDamageKHR
261187017518340 357 onMessageReceived
261187020825163 9948 queueBuffer
261187021345235 642 bufferLoad
261187121345235 153 query
...
```

The `QueryResultIterator` can also be converted to a Pandas DataFrame, which is
useful for data analysis and visualization. This requires `numpy` and `pandas`
to be installed.

```python
# Requires pandas and numpy
# pip install pandas numpy
import numpy as np

qr_it = tp.query('SELECT ts, dur, name FROM slice')
qr_df = qr_it.as_pandas_dataframe()
print(qr_df.to_string())
```

**Output**

```
ts                   dur                  name
-------------------- -------------------- ---------------------------
     261187017446933               358594 eglSwapBuffersWithDamageKHR
     261187017518340                  357 onMessageReceived
     261187020825163                 9948 queueBuffer
     261187021345235                  642 bufferLoad
     261187121345235                  153 query
     ...
```

You can use Pandas DataFrames to easily create visualizations from trace data.

```python
from perfetto.trace_processor import TraceProcessor
tp = TraceProcessor(trace='trace.perfetto-trace')

qr_it = tp.query('SELECT ts, value FROM counter WHERE track_id=50')
qr_df = qr_it.as_pandas_dataframe()
qr_df = qr_df.replace(np.nan,0)
qr_df = qr_df.set_index('ts')['value'].plot()
```

**Output**

![Graph made from the query results](/docs/images/example_pd_graph.png)

### Trace Summary

The `trace_summary()` function computes a structured summary of the trace. This
is useful for creating structured protobuf messages for consumption by other
tools. This function is the replacement for the deprecated `metric()` function.

See the [Trace Summarization docs](/docs/analysis/trace-summary.md) for a deep
dive into this feature.

```python
from perfetto.trace_processor import TraceProcessor

spec = """
metric_spec {
  id: "memory_per_process"
  dimensions: "process_name"
  value: "avg_rss_and_swap"
  query: {
    table: {
      table_name: "memory_rss_and_swap_per_process"
      module_name: "linux.memory.process"
    }
    group_by: {
      column_names: "process_name"
      aggregates: {
        column_name: "rss_and_swap"
        op: DURATION_WEIGHTED_MEAN
        result_column_name: "avg_rss_and_swap"
      }
    }
  }
}
"""
with TraceProcessor(trace='trace.perfetto-trace') as tp:
    summary = tp.trace_summary(specs=[spec])
    print(summary)
```

### Metatracing

Metatracing allows you to trace the performance of `trace_processor` itself.

```python
# Enable metatracing
tp.enable_metatrace()

# Run some queries
tp.query('select * from slice')
tp.query('select * from slice')

# Disable and read the metatrace
metatrace_bytes = tp.disable_and_read_metatrace()

# You can now load this into another TraceProcessor instance
with open('tp_metatrace.pftrace', 'wb') as f:
    f.write(metatrace_bytes)
tp_meta = TraceProcessor(trace='tp_metatrace.pftrace')
tp_meta.query('select * from slice')
```

### Metric (Deprecated)

The `metric()` function takes in a list of trace metrics and returns the results
as a Protobuf.

**Note:** this function is deprecated but there are no plans to remove it.
Consider using `trace_summary()` instead, which is an indirect replacement,
providing much of the same functionality but in a more flexible way.

```python
from perfetto.trace_processor import TraceProcessor
tp = TraceProcessor(trace='trace.perfetto-trace')

ad_cpu_metrics = tp.metric(['android_cpu'])
print(ad_cpu_metrics)
```

**Output**

```
metrics {
  android_cpu {
    process_info {
      name: "/system/bin/init"
      threads {
        name: "init"
        core {
          id: 1
          metrics {
            mcycles: 1
            runtime_ns: 570365
            min_freq_khz: 1900800
            max_freq_khz: 1900800
            avg_freq_khz: 1902017
          }
        }
        core {
          id: 3
          metrics {
            mcycles: 0
            runtime_ns: 366406
            min_freq_khz: 1900800
            max_freq_khz: 1900800
            avg_freq_khz: 1902908
          }
        }
        ...
      }
      ...
    }
    process_info {
      name: "/system/bin/logd"
      threads {
        name: "logd.writer"
        core {
          id: 0
          metrics {
            mcycles: 8
            runtime_ns: 33842357
            min_freq_khz: 595200
            max_freq_khz: 1900800
            avg_freq_khz: 1891825
          }
        }
        core {
          id: 1
          metrics {
            mcycles: 9
            runtime_ns: 36019300
            min_freq_khz: 1171200
            max_freq_khz: 1900800
            avg_freq_khz: 1887969
          }
        }
        ...
      }
      ...
    }
    ...
  }
}
```