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Optimize branch creation (#2101)

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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.
This commit is contained in:
Thang Pham
2022-07-19 14:56:25 -04:00
committed by GitHub
parent 98dd2e4f52
commit 160e52ec7e
6 changed files with 359 additions and 126 deletions
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10
libs/postgres_ffi/build.rs
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@@ -49,12 +49,12 @@ fn main() {
// Finding the location of C headers for the Postgres server:
// - if POSTGRES_INSTALL_DIR is set look into it, otherwise look into `<project_root>/tmp_install`
// - if there's a `bin/pg_config` file use it for getting include server, otherwise use `<project_root>/tmp_install/include/postgresql/server`
let mut pg_install_dir: PathBuf;
if let Some(postgres_install_dir) = env::var_os("POSTGRES_INSTALL_DIR") {
pg_install_dir = postgres_install_dir.into();
let mut pg_install_dir = if let Some(postgres_install_dir) = env::var_os("POSTGRES_INSTALL_DIR")
{
postgres_install_dir.into()
} else {
pg_install_dir = PathBuf::from("tmp_install")
}
PathBuf::from("tmp_install")
};
if pg_install_dir.is_relative() {
let cwd = env::current_dir().unwrap();