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pageserver: use histogram for background job semaphore waits #10697

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Feb 6, 2025
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pageserver: use histogram for background job semaphore waits #10697

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58 changes: 30 additions & 28 deletions pageserver/src/metrics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use std::sync::{Arc, Mutex};
use std::task::{Context, Poll};
use std::time::{Duration, Instant};

use enum_map::EnumMap;
use enum_map::{Enum as _, EnumMap};
use futures::Future;
use metrics::{
register_counter_vec, register_gauge_vec, register_histogram, register_histogram_vec,
Expand Down Expand Up @@ -104,7 +104,7 @@ pub(crate) static STORAGE_TIME_COUNT_PER_TIMELINE: Lazy<IntCounterVec> = Lazy::n
.expect("failed to define a metric")
});

// Buckets for background operations like compaction, GC, size calculation
// Buckets for background operation duration in seconds, like compaction, GC, size calculation.
const STORAGE_OP_BUCKETS: &[f64] = &[0.010, 0.100, 1.0, 10.0, 100.0, 1000.0];

pub(crate) static STORAGE_TIME_GLOBAL: Lazy<HistogramVec> = Lazy::new(|| {
Expand Down Expand Up @@ -236,7 +236,7 @@ pub(crate) static GET_VECTORED_LATENCY: Lazy<GetVectoredLatency> = Lazy::new(||

GetVectoredLatency {
map: EnumMap::from_array(std::array::from_fn(|task_kind_idx| {
let task_kind = <TaskKind as enum_map::Enum>::from_usize(task_kind_idx);
let task_kind = TaskKind::from_usize(task_kind_idx);

if GetVectoredLatency::TRACKED_TASK_KINDS.contains(&task_kind) {
let task_kind = task_kind.into();
Expand All @@ -259,7 +259,7 @@ pub(crate) static SCAN_LATENCY: Lazy<ScanLatency> = Lazy::new(|| {

ScanLatency {
map: EnumMap::from_array(std::array::from_fn(|task_kind_idx| {
let task_kind = <TaskKind as enum_map::Enum>::from_usize(task_kind_idx);
let task_kind = TaskKind::from_usize(task_kind_idx);

if ScanLatency::TRACKED_TASK_KINDS.contains(&task_kind) {
let task_kind = task_kind.into();
Expand Down Expand Up @@ -300,10 +300,10 @@ static PAGE_CACHE_READ_ACCESSES: Lazy<IntCounterVec> = Lazy::new(|| {

pub(crate) static PAGE_CACHE: Lazy<PageCacheMetrics> = Lazy::new(|| PageCacheMetrics {
map: EnumMap::from_array(std::array::from_fn(|task_kind| {
let task_kind = <TaskKind as enum_map::Enum>::from_usize(task_kind);
let task_kind = TaskKind::from_usize(task_kind);
let task_kind: &'static str = task_kind.into();
EnumMap::from_array(std::array::from_fn(|content_kind| {
let content_kind = <PageContentKind as enum_map::Enum>::from_usize(content_kind);
let content_kind = PageContentKind::from_usize(content_kind);
let content_kind: &'static str = content_kind.into();
PageCacheMetricsForTaskKind {
read_accesses_immutable: {
Expand Down Expand Up @@ -1913,7 +1913,7 @@ pub(crate) static COMPUTE_COMMANDS_COUNTERS: Lazy<ComputeCommandCounters> = Lazy

ComputeCommandCounters {
map: EnumMap::from_array(std::array::from_fn(|i| {
let command = <ComputeCommandKind as enum_map::Enum>::from_usize(i);
let command = ComputeCommandKind::from_usize(i);
let command_str: &'static str = command.into();
inner.with_label_values(&[command_str])
})),
Expand Down Expand Up @@ -2213,13 +2213,13 @@ pub(crate) static TENANT_TASK_EVENTS: Lazy<IntCounterVec> = Lazy::new(|| {

pub struct BackgroundLoopSemaphoreMetrics {
counters: EnumMap<BackgroundLoopKind, IntCounterPair>,
durations: EnumMap<BackgroundLoopKind, Counter>,
durations: EnumMap<BackgroundLoopKind, Histogram>,
waiting_tasks: EnumMap<BackgroundLoopKind, IntGauge>,
running_tasks: EnumMap<BackgroundLoopKind, IntGauge>,
}

pub(crate) static BACKGROUND_LOOP_SEMAPHORE: Lazy<BackgroundLoopSemaphoreMetrics> = Lazy::new(
|| {
pub(crate) static BACKGROUND_LOOP_SEMAPHORE: Lazy<BackgroundLoopSemaphoreMetrics> =
Lazy::new(|| {
let counters = register_int_counter_pair_vec!(
"pageserver_background_loop_semaphore_wait_start_count",
"Counter for background loop concurrency-limiting semaphore acquire calls started",
Expand All @@ -2229,10 +2229,11 @@ pub(crate) static BACKGROUND_LOOP_SEMAPHORE: Lazy<BackgroundLoopSemaphoreMetrics
)
.unwrap();

let durations = register_counter_vec!(
"pageserver_background_loop_semaphore_wait_duration_seconds",
"Sum of wall clock time spent waiting on the background loop concurrency-limiting semaphore acquire calls",
let durations = register_histogram_vec!(
"pageserver_background_loop_semaphore_wait_seconds",
"Seconds spent waiting on background loop semaphore acquisition",
&["task"],
vec![0.01, 1.0, 5.0, 10.0, 30.0, 60.0, 180.0, 300.0, 600.0],
)
.unwrap();

Expand All @@ -2251,25 +2252,24 @@ pub(crate) static BACKGROUND_LOOP_SEMAPHORE: Lazy<BackgroundLoopSemaphoreMetrics
.unwrap();

BackgroundLoopSemaphoreMetrics {
counters: enum_map::EnumMap::from_array(std::array::from_fn(|i| {
let kind = <BackgroundLoopKind as enum_map::Enum>::from_usize(i);
counters: EnumMap::from_array(std::array::from_fn(|i| {
let kind = BackgroundLoopKind::from_usize(i);
counters.with_label_values(&[kind.into()])
})),
durations: enum_map::EnumMap::from_array(std::array::from_fn(|i| {
let kind = <BackgroundLoopKind as enum_map::Enum>::from_usize(i);
durations: EnumMap::from_array(std::array::from_fn(|i| {
let kind = BackgroundLoopKind::from_usize(i);
durations.with_label_values(&[kind.into()])
})),
waiting_tasks: enum_map::EnumMap::from_array(std::array::from_fn(|i| {
let kind = <BackgroundLoopKind as enum_map::Enum>::from_usize(i);
waiting_tasks: EnumMap::from_array(std::array::from_fn(|i| {
let kind = BackgroundLoopKind::from_usize(i);
waiting_tasks.with_label_values(&[kind.into()])
})),
running_tasks: enum_map::EnumMap::from_array(std::array::from_fn(|i| {
let kind = <BackgroundLoopKind as enum_map::Enum>::from_usize(i);
running_tasks: EnumMap::from_array(std::array::from_fn(|i| {
let kind = BackgroundLoopKind::from_usize(i);
running_tasks.with_label_values(&[kind.into()])
})),
}
},
);
});

impl BackgroundLoopSemaphoreMetrics {
/// Starts recording semaphore metrics. Call `acquired()` on the returned recorder when the
Expand Down Expand Up @@ -2304,11 +2304,13 @@ impl<'a> BackgroundLoopSemaphoreMetricsRecorder<'a> {
}

/// Signals that the semaphore has been acquired, and updates relevant metrics.
pub fn acquired(&mut self) {
pub fn acquired(&mut self) -> Duration {
let waited = self.start.elapsed();
self.wait_counter_guard.take().expect("already acquired");
self.metrics.durations[self.task].inc_by(self.start.elapsed().as_secs_f64());
self.metrics.durations[self.task].observe(waited.as_secs_f64());
self.metrics.waiting_tasks[self.task].dec();
self.metrics.running_tasks[self.task].inc();
waited
}
}

Expand All @@ -2317,7 +2319,7 @@ impl Drop for BackgroundLoopSemaphoreMetricsRecorder<'_> {
fn drop(&mut self) {
if self.wait_counter_guard.take().is_some() {
// Waiting.
self.metrics.durations[self.task].inc_by(self.start.elapsed().as_secs_f64());
self.metrics.durations[self.task].observe(self.start.elapsed().as_secs_f64());
self.metrics.waiting_tasks[self.task].dec();
} else {
// Running.
Expand Down Expand Up @@ -2570,7 +2572,7 @@ pub(crate) static WAL_REDO_PROCESS_LAUNCH_DURATION_HISTOGRAM: Lazy<Histogram> =

pub(crate) struct WalRedoProcessCounters {
pub(crate) started: IntCounter,
pub(crate) killed_by_cause: enum_map::EnumMap<WalRedoKillCause, IntCounter>,
pub(crate) killed_by_cause: EnumMap<WalRedoKillCause, IntCounter>,
pub(crate) active_stderr_logger_tasks_started: IntCounter,
pub(crate) active_stderr_logger_tasks_finished: IntCounter,
}
Expand Down Expand Up @@ -2612,7 +2614,7 @@ impl Default for WalRedoProcessCounters {
Self {
started,
killed_by_cause: EnumMap::from_array(std::array::from_fn(|i| {
let cause = <WalRedoKillCause as enum_map::Enum>::from_usize(i);
let cause = WalRedoKillCause::from_usize(i);
let cause_str: &'static str = cause.into();
killed.with_label_values(&[cause_str])
})),
Expand Down
38 changes: 28 additions & 10 deletions pageserver/src/tenant/tasks.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@

use std::ops::ControlFlow;
use std::str::FromStr;
use std::sync::Arc;
use std::sync::{Arc, Mutex};
use std::time::{Duration, Instant};

use crate::context::{DownloadBehavior, RequestContext};
Expand All @@ -14,9 +14,11 @@ use crate::tenant::throttle::Stats;
use crate::tenant::timeline::compaction::CompactionOutcome;
use crate::tenant::timeline::CompactionError;
use crate::tenant::{Tenant, TenantState};
use once_cell::sync::Lazy;
use rand::Rng;
use tokio_util::sync::CancellationToken;
use tracing::*;
use utils::rate_limit::RateLimit;
use utils::{backoff, completion, pausable_failpoint};

static CONCURRENT_BACKGROUND_TASKS: once_cell::sync::Lazy<tokio::sync::Semaphore> =
Expand All @@ -41,7 +43,16 @@ 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, enum_map::Enum)]
#[derive(
Debug,
PartialEq,
Eq,
Clone,
Copy,
strum_macros::IntoStaticStr,
strum_macros::Display,
enum_map::Enum,
)]
#[strum(serialize_all = "snake_case")]
pub(crate) enum BackgroundLoopKind {
Compaction,
Expand All @@ -55,12 +66,6 @@ pub(crate) enum BackgroundLoopKind {
SecondaryDownload,
}

impl BackgroundLoopKind {
fn as_static_str(&self) -> &'static str {
self.into()
}
}

pub struct BackgroundLoopSemaphorePermit<'a> {
_permit: tokio::sync::SemaphorePermit<'static>,
_recorder: BackgroundLoopSemaphoreMetricsRecorder<'a>,
Expand All @@ -71,6 +76,11 @@ pub(crate) async fn concurrent_background_tasks_rate_limit_permit(
loop_kind: BackgroundLoopKind,
_ctx: &RequestContext,
) -> BackgroundLoopSemaphorePermit<'static> {
// TODO: use a lower threshold and remove the pacer once we resolve some blockage.
const WARN_THRESHOLD: Duration = Duration::from_secs(600);
static WARN_PACER: Lazy<Mutex<RateLimit>> =
Lazy::new(|| Mutex::new(RateLimit::new(Duration::from_secs(10))));

let mut recorder = crate::metrics::BACKGROUND_LOOP_SEMAPHORE.record(loop_kind);

if loop_kind == BackgroundLoopKind::InitialLogicalSizeCalculation {
Expand All @@ -82,7 +92,15 @@ pub(crate) async fn concurrent_background_tasks_rate_limit_permit(
.acquire()
.await
.expect("should never close");
recorder.acquired();

let waited = recorder.acquired();
if waited >= WARN_THRESHOLD {
let waited = waited.as_secs_f64();
WARN_PACER
.lock()
.unwrap()
.call(|| warn!("{loop_kind} task waited {waited:.3}s for semaphore permit"));
}

BackgroundLoopSemaphorePermit {
_permit: permit,
Expand Down Expand Up @@ -628,7 +646,7 @@ pub(crate) fn warn_when_period_overrun(
"task iteration took longer than the configured period"
);
crate::metrics::BACKGROUND_LOOP_PERIOD_OVERRUN_COUNT
.with_label_values(&[task.as_static_str(), &format!("{}", period.as_secs())])
.with_label_values(&[task.into(), &format!("{}", period.as_secs())])
.inc();
}
}
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