Alexey Kondratov
0ca342260c
## Problem
In 89275f6c1e we fixed an issue, when we were dropping db in Postgres
even though cplane request failed. Yet, it introduced a new problem that
we now de-register db in cplane even if we didn't actually drop it in
Postgres.
## Summary of changes
Here we revert extension change, so we now again may leave db in invalid
state after failed drop. Instead, `compute_ctl` is now responsible for
cleaning up invalid databases during full configuration. Thus, there are
two ways of recovering from failed DROP DATABASE:
1. User can just repeat DROP DATABASE, same as in Vanilla Postgres.
2. If they didn't, then on next full configuration (dbs / roles changes
in the API; password reset; or data availability check) invalid db
will be cleaned up in the Postgres and re-created by `compute_ctl`. So
again it follows pretty much the same semantics as Vanilla Postgres --
you need to drop it again after failed drop.
That way, we have a recovery trajectory for both problems.
See this commit for info about `invalid` db state:
https://github.com/postgres/postgres/commit/a4b4cc1d60f7e8ccfcc8ff8cb80c28ee411ad9a9
According to it:
> An invalid database cannot be connected to anymore, but can still be
dropped.
While on it, this commit also fixes another issue, when `compute_ctl`
was trying to connect to databases with `ALLOW CONNECTIONS false`. Now
it will just skip them.
Fixes #5435
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_ctlaccepts 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
PGDATAdirectory. - Sync safekeepers and get commit LSN.
- Get
basebackupfrom pageserver using the returned on the previous step LSN. - Try to start
postgresand wait until it is ready to accept connections. - Check and alter/drop/create roles and databases.
- Hang waiting on the
postmasterprocess to exit.
Also compute_ctl spawns two separate service threads:
compute-monitorchecks the last Postgres activity timestamp and saves it into the sharedComputeNode;http-endpointruns 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
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