rosbag2_storage: set MCAP as default plugin

[james-rms]

switches the default storage plugin from sqlite3 to mcap.

Reason for change

Benchmarks suggest that MCAP can support higher write throughput than the sqlite3 plugin in its default configuration, while also bringing the following other benefits:

• Append-only write behavior ensures that only the last few messages written can be corrupted in the case of a power outage or recorder crash. This is similar to the corruption guarantees offered by SQLite3 in WAL mode, which is what is used in the resilient SQLite storage plugin preset.
• Ability to enable chunk compression, which should be more space-efficient than message compression for bags with many small messages. This also enables reader to use the message index, unlike file-level compression.
• Record message schemas to the bag by default, enabling applications outside the ROS 2 workspace to read message content.

Benchmarks

Read the benchmarking analysis that lead to this conclusion here.

rosbag2_performance_benchmarking

There is a set of pre-existing benchmarks in the rosbag2 repo here: https://github.com/ros2/rosbag2/tree/rolling/rosbag2_performance/rosbag2_performance_benchmarking

We've run these in an attempt to compare the performance of MCAP against SQLite on these metrics, but at this point the results appear to be pure noise. A full analysis of why will be published to mcap.dev shortly, but for now the news is that we have not succeeded in producing a statistically significant difference in results between MCAP and SQLite.

TODO

• Remove rosbag2_tests direct dependence on sqlite3 #1112
• ros2 bag convert cannot read the input file if the input MCAP is not indexed ros-tooling/rosbag2_storage_mcap#61
• Migrate to rosbag2 repo ros-tooling/rosbag2_storage_mcap#63
• Add integration test for mcap storage plugin #1185
• Parametrize rosbag2_tests

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/psa-default-ros-2-bag-storage-format-is-changing-to-mcap-in-iron/28489/1

[MichaelOrlov]

@james-rms Am I understand correctly that we have not yet finished with adding MCAP to the rosbag2_tests parametrization?
i.e. not ready yet to switch to the MCAP by default.

[james-rms]

Yes - will convert to draft until that lands.

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/ros-2-tsc-meeting-minutes-2022-12-15/28840/1

[james-rms]

Gist: https://gist.githubusercontent.com/james-rms/c4e9cba9397445f51066232f1068771d/raw/9eddb125272e274d3128068668a045b681f124fc/ros2.repos
BUILD args: --packages-above-and-dependencies ros2bag rosbag2_cpp rosbag2_py rosbag2_storage rosbag2_storage_default_plugins rosbag2_tests rosbag2_transport
TEST args: --packages-above ros2bag rosbag2_cpp rosbag2_py rosbag2_storage rosbag2_storage_default_plugins rosbag2_tests rosbag2_transport
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/11309

• Linux
• Linux-aarch64
• Windows

[MichaelOrlov]

Blessing. 🤞

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/ros-2-tsc-meeting-minutes-2023-01-19/29423/1