# Refs
- fixes https://github.com/neondatabase/neon/issues/11395
# Problem
Since 2025-03-10, we have observed increased flakiness of
`test_pageserver_getpage_throttle`.
The test is timing-dependent by nature, and was hitting the
```
assert duration_secs >= 10 * actual_smgr_query_seconds, (
"smgr metrics should not include throttle wait time"
)
```
quite frequently.
# Analysis
These failures are not reproducible.
In this PR's history is a commit that reran the test 100 times without
requiring a single retry.
In https://github.com/neondatabase/neon/issues/11395 there is a link to
a query to the test results database.
It shows that the flakiness was not constant, but rather episodic:
2025-03-{10,11,12,13} 2025-03-{19,20,21} 2025-03-31 and 2025-04-01.
To me, this suggests variability in available CPU.
# Solution
The point of the offending assertion is to ensure that most of the
request latency is spent on throttling, because testing of the
throttling mechanism is the point of the test.
The `10` magic number means at most 10% of mean latency may be spent on
request processing.
Ideally we would control the passage of time (virtual clock source) to
make this test deterministic.
But I don't see that happening in our regression test setup.
So, this PR de-flakes the test as follows:
- allot up to 66% of mean latency for request processing
- increase duration from 10s to 20s, hoping to get better protection
from momentary CPU spikes in noisy neighbor tests or VMs on the runner
host
As a drive-by, switch to `pytest.approx` and remove one self-test
assertion I can't make sense of anymore.
8884865bca