merlimat opened a new pull request, #25669:
URL: https://github.com/apache/pulsar/pull/25669
### Motivation
The existing `Backoff` class always subtracts up to 10% jitter from the next
delay, never adds, and skips jitter on the first invocation entirely (the
result is clamped back up to `initialDelay`). When many clients restart
together, the first reconnect attempt fires at the exact configured initial
delay — defeating the point of jitter. The jitter percentage was also
hard-coded.
### Modifications
- `Backoff` takes a configurable `jitterPercent` (default 10).
- Jitter is applied symmetrically as `±jitterPercent/2`: the underlying
delay is multiplied by a uniform random factor in `[1 − jitterPercent/200, 1 +
jitterPercent/200)`.
- Jitter is applied on every call, including the first. The previous
`Math.max(initial, …)` clamp is removed; the returned value may now be slightly
below `initialDelay` or slightly above `maxBackoff`.
- `BackoffPolicy` (v5 client API) gains a `jitterPercent` field with a
`withJitter(double)` helper. Existing factory methods seed the default jitter
so callers are unaffected.
The new `BackoffPolicy.jitterPercent` is currently API-shape only: the
connection-backoff path is still TODO'd in `PulsarClientBuilderV5`, and the
redelivery-backoff path goes through `MultiplierRedeliveryBackoff` which has no
jitter support. Wiring is left for a follow-up.
### Verifying this change
This change added tests and can be verified as follows:
- New unit tests in `BackoffTest`:
- `jitterIsAppliedSymmetricallyOnFirstCall` — across 500 resets verifies
values both above and below the base, all within `[base · 0.9, base · 1.1]` for
`jitterPercent=20`.
- `jitterPercentZeroDisablesJitter` — verifies the disable path returns
the exact base.
- `negativeJitterIsRejected` — validation.
- Existing tests updated to set `jitterPercent(0)` for deterministic
exponential-progression and mandatory-stop checks.
### Does this pull request potentially affect one of the following parts:
- [x] The public API
`org.apache.pulsar.common.util.Backoff` and
`org.apache.pulsar.client.api.v5.config.BackoffPolicy` gain new optional
fields/builder methods. Existing callers are unaffected (defaults preserve the
10% magnitude, though the direction now spans `±5%` instead of `−10%`).
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