Compute node tools

Postgres wrapper (compute_ctl) is intended to be run as a Docker entrypoint or as a systemd ExecStart option. It will handle all the Neon specifics during compute node initialization:

• compute_ctl accepts cluster (compute node) specification as a JSON file.
• Every start is a fresh start, so the data directory is removed and initialized again on each run.
• Next it will put configuration files into the PGDATA directory.
• Sync safekeepers and get commit LSN.
• Get basebackup from pageserver using the returned on the previous step LSN.
• Try to start postgres and wait until it is ready to accept connections.
• Check and alter/drop/create roles and databases.
• Hang waiting on the postmaster process to exit.

Also compute_ctl spawns two separate service threads:

• compute-monitor checks the last Postgres activity timestamp and saves it into the shared ComputeNode;
• http-endpoint runs a Hyper HTTP API server, which serves readiness and the last activity requests.

If AUTOSCALING environment variable is set, compute_ctl will start the vm-monitor located in [neon/libs/vm_monitor]. For VM compute nodes, vm-monitor communicates with the VM autoscaling system. It coordinates downscaling and requests immediate upscaling under resource pressure.

Usage example:

compute_ctl -D /var/db/postgres/compute \
            -C 'postgresql://cloud_admin@localhost/postgres' \
            -S /var/db/postgres/specs/current.json \
            -b /usr/local/bin/postgres

State Diagram

Computes can be in various states. Below is a diagram that details how a compute moves between states.

%% https://mermaid.js.org/syntax/stateDiagram.html
stateDiagram-v2
  [*] --> Empty : Compute spawned
  Empty --> ConfigurationPending : Waiting for compute spec
  ConfigurationPending --> Configuration : Received compute spec
  Configuration --> Failed : Failed to configure the compute
  Configuration --> Running : Compute has been configured
  Empty --> Init : Compute spec is immediately available
  Empty --> TerminationPending : Requested termination
  Init --> Failed : Failed to start Postgres
  Init --> Running : Started Postgres
  Running --> TerminationPending : Requested termination
  TerminationPending --> Terminated : Terminated compute
  Failed --> [*] : Compute exited
  Terminated --> [*] : Compute exited

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Tests

Cargo formatter:

cargo fmt

Run tests:

cargo test

Clippy linter:

cargo clippy --all --all-targets -- -Dwarnings -Drust-2018-idioms

Cross-platform compilation

Imaging that you are on macOS (x86) and you want a Linux GNU (x86_64-unknown-linux-gnu platform in rust terminology) executable.

Using docker

You can use a throw-away Docker container (rustlang/rust image) for doing that:

docker run --rm \
    -v $(pwd):/compute_tools \
    -w /compute_tools \
    -t rustlang/rust:nightly cargo build --release --target=x86_64-unknown-linux-gnu

or one-line:

docker run --rm -v $(pwd):/compute_tools -w /compute_tools -t rust:latest cargo build --release --target=x86_64-unknown-linux-gnu

Using rust native cross-compilation

Another way is to add x86_64-unknown-linux-gnu target on your host system:

rustup target add x86_64-unknown-linux-gnu

Install macOS cross-compiler toolchain:

brew tap SergioBenitez/osxct
brew install x86_64-unknown-linux-gnu

And finally run cargo build:

CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER=x86_64-unknown-linux-gnu-gcc cargo build --target=x86_64-unknown-linux-gnu --release