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fix: do not create metrics contention from background task permit (#7730)

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The background task loop permit metrics do two of `with_label_values`
very often. Change the codepath to cache the counters on first access
into a `Lazy` with `enum_map::EnumMap`. The expectation is that this
should not fix for metric collection failures under load, but it doesn't
hurt.

Cc: #7161
This commit is contained in:
Joonas Koivunen
2024-05-13 17:49:50 +03:00
committed by GitHub
parent 55ba885f6b
commit 4d8a10af1c
1 changed files with 12 additions and 6 deletions
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18
pageserver/src/tenant/tasks.rs
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@@ -41,7 +41,7 @@ static CONCURRENT_BACKGROUND_TASKS: once_cell::sync::Lazy<tokio::sync::Semaphore
tokio::sync::Semaphore::new(permits)
});
#[derive(Debug, PartialEq, Eq, Clone, Copy, strum_macros::IntoStaticStr)]
#[derive(Debug, PartialEq, Eq, Clone, Copy, strum_macros::IntoStaticStr, enum_map::Enum)]
#[strum(serialize_all = "snake_case")]
pub(crate) enum BackgroundLoopKind {
Compaction,
@@ -57,19 +57,25 @@ pub(crate) enum BackgroundLoopKind {
impl BackgroundLoopKind {
fn as_static_str(&self) -> &'static str {
let s: &'static str = self.into();
s
self.into()
}
}
static PERMIT_GAUGES: once_cell::sync::Lazy<
enum_map::EnumMap<BackgroundLoopKind, metrics::IntCounterPair>,
> = once_cell::sync::Lazy::new(|| {
enum_map::EnumMap::from_array(std::array::from_fn(|i| {
let kind = <BackgroundLoopKind as enum_map::Enum>::from_usize(i);
crate::metrics::BACKGROUND_LOOP_SEMAPHORE_WAIT_GAUGE.with_label_values(&[kind.into()])
}))
});
/// Cancellation safe.
pub(crate) async fn concurrent_background_tasks_rate_limit_permit(
loop_kind: BackgroundLoopKind,
_ctx: &RequestContext,
) -> tokio::sync::SemaphorePermit<'static> {
let _guard = crate::metrics::BACKGROUND_LOOP_SEMAPHORE_WAIT_GAUGE
.with_label_values(&[loop_kind.as_static_str()])
.guard();
let _guard = PERMIT_GAUGES[loop_kind].guard();
pausable_failpoint!(
"initial-size-calculation-permit-pause",