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Profiling Cookbook

docs/source/library-user-guide/profiling.md

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Profiling Cookbook

The section contains examples how to perform CPU profiling for Apache DataFusion on different operating systems.

Building a flame graph

Video: how to CPU profile DataFusion with a Flamegraph

A flamegraph is a visual representation of which functions are being run You can create flamegraphs in many ways; The instructions below are for cargo-flamegraph which results in images such as this:

MacOS

Step 1: Install the flamegraph Tool

To install flamegraph, run:

shell
cargo install flamegraph

Step 2: Prepare Your Environment

Ensure that you're in the directory containing the necessary data files for your DataFusion query. The flamegraph tool will profile the execution of your query against this data.

Step 3: Running the Flamegraph Tool

To generate a flamegraph, you'll need to use the -- separator to pass arguments to the binary you're profiling. For datafusion-cli, you need to make sure to run the command with sudo permissions (especially on macOS, where DTrace requires elevated privileges).

Here is a general example:

shell
sudo flamegraph -- datafusion-cli -f <path_to_sql_file/sql_file.sql>

Example: Generating a Flamegraph for a Specific Query

Here is an example using 28.sql:

shell
sudo flamegraph -- datafusion-cli -f 28.sql

You can also invoke the flamegraph tool with cargo to profile a specific test or benchmark.

Example: Flamegraph for a specific test:

bash
CARGO_PROFILE_RELEASE_DEBUG=true cargo flamegraph --root --unit-test datafusion  -- dataframe::tests::test_array_agg

Example: Flamegraph for a benchmark

bash
CARGO_PROFILE_RELEASE_DEBUG=true cargo flamegraph --root --bench sql_planner -- --bench

CPU profiling with XCode Instruments

Video: how to CPU profile DataFusion with XCode Instruments

Profiling using Samply cross platform profiler

There is an opportunity to build flamegraphs, call trees and stack charts on any platform using Samply

Install Samply profiler

shell
cargo install --locked samply

More Samply installation options

Run the profiler

shell
samply record --profile profiling ./my-application my-arguments

Profile the benchmark

Set up benchmarks if not yet done

Example: Profile Q22 query from TPC-H benchmark. Note: --profile profiling to profile release optimized artifact with debug symbols

shell
cargo build --profile profiling --bin tpch
samply record ./target/profiling/tpch benchmark datafusion --iterations 5 --path datafusion/benchmarks/data/tpch_sf10 --prefer_hash_join true --format parquet -o datafusion/benchmarks/results/dev2/tpch_sf10.json --query 22

After sampling has completed the Samply starts a local server and navigates to the profiler

shell
Local server listening at http://127.0.0.1:3000

Note: The Firefox profiler cannot be opened in Safari, please use Chrome or Firefox instead