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pageserver: improve pageserver_smgr_query_seconds buckets (#11680)

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## Problem

The `pageserver_smgr_query_seconds` buckets are too coarse, using powers
of 10: 1 µs, 10 µs, 100 µs, 1 ms, 10 ms, 100 ms, 1 s, 10 s, 100 s. This
is one of our most crucial latency metrics, and needs better resolution.

Touches #11594.

## Summary of changes

This patch uses buckets with better resolution around 1 ms (the typical
latency):

* 0.6 ms
* 1 ms
* 3 ms
* 6 ms
* 10 ms
* 30 ms
* 100 ms
* 1 s
* 3 s

These will be the same as the compute's `compute_getpage_wait_seconds`,
to make them comparable across the compute and Pageserver:
https://github.com/neondatabase/flux-fleet/pull/579. We sacrifice
buckets above 3 s, since these can already be considered "too slow".

This does not change the previously used `CRITICAL_OP_BUCKETS`, which is
also used for other operations on different timescales (e.g. LSN waits).
We should consider replacing this with more appropriate buckets for
specific operations, since it covers a large span with low resolution.
This commit is contained in:
Erik Grinaker
2025-04-28 13:52:44 +02:00
committed by GitHub
parent 32393b4393
commit 606f14034e
1 changed files with 6 additions and 2 deletions
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8
pageserver/src/metrics.rs
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@@ -1774,8 +1774,12 @@ static SMGR_QUERY_STARTED_PER_TENANT_TIMELINE: Lazy<IntCounterVec> = Lazy::new(|
.expect("failed to define a metric")
});
// Alias so all histograms recording per-timeline smgr timings use the same buckets.
static SMGR_QUERY_TIME_PER_TENANT_TIMELINE_BUCKETS: &[f64] = CRITICAL_OP_BUCKETS;
/// Per-timeline smgr histogram buckets should be the same as the compute buckets, such that the
/// metrics are comparable across compute and Pageserver. See also:
/// <https://github.com/neondatabase/neon/blob/1a87975d956a8ad17ec8b85da32a137ec4893fcc/pgxn/neon/neon_perf_counters.h#L18-L27>
/// <https://github.com/neondatabase/flux-fleet/blob/556182a939edda87ff1d85a6b02e5cec901e0e9e/apps/base/compute-metrics/scrape-compute-sql-exporter.yaml#L29-L35>
static SMGR_QUERY_TIME_PER_TENANT_TIMELINE_BUCKETS: &[f64] =
&[0.0006, 0.001, 0.003, 0.006, 0.01, 0.03, 0.1, 1.0, 3.0];
static SMGR_QUERY_TIME_PER_TENANT_TIMELINE: Lazy<HistogramVec> = Lazy::new(|| {
register_histogram_vec!(