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## Source tree layout
Below you will find a brief overview of each subdir in the source tree in alphabetical order.
`/control_plane`:
Local control plane.
Functions to start, configure and stop pageserver and postgres instances running as a local processes.
Intended to be used in integration tests and in CLI tools for local installations.
`/docs`:
Documentaion of the Zenith features and concepts.
Now it is mostly dev documentation.
`/monitoring`:
TODO
`/pageserver`:
Zenith storage service.
The pageserver has a few different duties:
- Store and manage the data.
- Generate a tarball with files needed to bootstrap ComputeNode.
- Respond to GetPage@LSN requests from the Compute Nodes.
- Receive WAL from the WAL service and decode it.
- Replay WAL that's applicable to the chunks that the Page Server maintains
For more detailed info, see `/pageserver/README`
`/postgres_ffi`:
Utility functions for interacting with PostgreSQL file formats.
Misc constants, copied from PostgreSQL headers.
`/proxy`:
Postgres protocol proxy/router.
This service listens psql port, can check auth via external service
and create new databases and accounts (control plane API in our case).
`/test_runner`:
Integration tests, written in Python using the `pytest` framework.
`/vendor/postgres`:
PostgreSQL source tree, with the modifications needed for Zenith.
`/vendor/postgres/contrib/zenith`:
PostgreSQL extension that implements storage manager API and network communications with remote page server.
`/vendor/postgres/contrib/zenith_test_utils`:
PostgreSQL extension that contains functions needed for testing and debugging.
`/walkeeper`:
The zenith WAL service that receives WAL from a primary compute nodes and streams it to the pageserver.
It acts as a holding area and redistribution center for recently generated WAL.
For more detailed info, see `/walkeeper/README`
`/workspace_hack`:
The workspace_hack crate exists only to pin down some dependencies.
`/zenith`
Main entry point for the 'zenith' CLI utility.
TODO: Doesn't it belong to control_plane?
`/zenith_metrics`:
Helpers for exposing Prometheus metrics from the server.
`/zenith_utils`:
Helpers that are shared between other crates in this repository.
## Using Python
Note that Debian/Ubuntu Python packages are stale, as it commonly happens,
so manual installation of dependencies is not recommended.
A single virtual environment with all dependencies is described in the single `Pipfile`.
### Prerequisites
- Install Python 3.7 (the minimal supported version)
- Later version (e.g. 3.8) is ok if you don't write Python code
- You can install Python 3.7 separately, e.g.:
```bash
# In Ubuntu
sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt update
sudo apt install python3.7
```
- Install `pipenv`
- Exact version of `pipenv` is not important, you can use Debian/Ubuntu package `pipenv`.
- Install dependencies via either
* `pipenv --python 3.7 install --dev` if you will write Python code, or
* `pipenv install` if you only want to run Python scripts and don't have Python 3.7.
Run `pipenv shell` to activate the virtual environment.
Alternatively, use `pipenv run` to run a single command in the venv, e.g. `pipenv run pytest`.
### Obligatory checks
We force code formatting via `yapf` and type hints via `mypy`.
Run the following commands in the repository's root (next to `setup.cfg`):
```bash
pipenv run yapf -ri . # All code is reformatted
pipenv run mypy . # Ensure there are no typing errors
```
**WARNING**: do not run `mypy` from a directory other than the root of the repository.
Otherwise it will not find its configuration.
Also consider:
* Running `flake8` (or a linter of your choice, e.g. `pycodestyle`) and fixing possible defects, if any.
* Adding more type hints to your code to avoid `Any`.
### Changing dependencies
You have to update `Pipfile.lock` if you have changed `Pipfile`:
```bash
pipenv --python 3.7 install --dev # Re-create venv for Python 3.7 and install recent pipenv inside
pipenv run pipenv --version # Should be at least 2021.5.29
pipenv run pipenv lock # Regenerate Pipfile.lock
```
As the minimal supported version is Python 3.7 and we use it in CI,
you have to use a Python 3.7 environment when updating `Pipfile.lock`.
Otherwise some back-compatibility packages will be missing.
It is also important to run recent `pipenv`.
Older versions remove markers from `Pipfile.lock`.