Resolves#2054
**Context**: branch creation needs to wait for GC to acquire `gc_cs` lock, which prevents creating new timelines during GC. However, because individual timeline GC iteration also requires `compaction_cs` lock, branch creation may also need to wait for compactions of multiple timelines. This results in large latency when creating a new branch, which we advertised as *"instantly"*.
This PR optimizes the latency of branch creation by separating GC into two phases:
1. Collect GC data (branching points, cutoff LSNs, etc)
2. Perform GC for each timeline
The GC bottleneck comes from step 2, which must wait for compaction of multiple timelines. This PR modifies the branch creation and GC functions to allow GC to hold the GC lock only in step 1. As a result, branch creation doesn't need to wait for compaction to finish but only needs to wait for GC data collection step, which is fast.
Simplifies the workflow. Makes the overall build a little faster, as
the build_postgres step doesn't need to upload the pg.tgz artifact,
and the build_neon step doesn't need to download it again.
This effectively reverts commit a490f64a68. That commit changed the
workflow so that the Postgres binaries were not included in the
neon.tgz artifact. With this commit, the pg.tgz artifact is gone, and
the Postgres binaries are part of neon.tgz again.
The "cargo metadata" and "cargo test --no-run" are used in the workflow
to just list names of the final binaries, but unless the same cargo
options like --release or --debug are used in those calls, they will in
fact recompile everything.
neon.tgz artifact in the github workflow included the contents of
'tmp_install', but that seems pointless, because the same files are
included earlier already in the pg.tgz artifact.
Uploading large artifacts is slow in github actions. To speed that up,
make the artifact smaller.
The code coverage tool doesn't require debug symbols, so remove them.
We've discussed doing the same for *all* binaries, but it's nice to
have debugging symbols for debugging purposes, and so that you get
more complete stack traces. The discussion is ongoing, but let's at
least do this for the test symbols now.
See https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#concurrency
* Previously there was a single concurrency group per each branch.
As the `main` branch got pushed into frequently, very few commits got
tested to the end. It resulted in "broken" `main` branch as there were
no fully successful workflow runs.
Now the `main` branch gets a separate concurrency group for each commit.
* As GitHub Actions syntax does not have the conditional operator, it is
emulated via logical and/or operations. Although undocumented, they
return one of their operands instead of plain true/false.
* Replace 3-space indentation with 2-space indentation while we are here
to be consistent with the rest of the file.
We need both storage **and** compute images for deploy, because control plane
picks the compute version based on the storage version. If it notices a fresh
storage it may bump the compute version. And if compute image failed to build
it may break things badly.
