tanmayrauth commented on code in PR #1640:
URL: https://github.com/apache/iceberg-go/pull/1640#discussion_r3717179624
##########
catalog/hive/lock.go:
##########
@@ -160,6 +165,60 @@ func calculateBackoff(attempt int, minWait, maxWait
time.Duration) time.Duration
return minWait << attempt
}
+// applyJitter spreads a backoff interval by adding a random amount on top of
it,
+// bounded so the result never exceeds maxWait.
+//
+// calculateBackoff is a pure function of the attempt number and the configured
+// bounds, so every client waiting on the same table lock computes an identical
+// sequence of delays. Contention is the precondition for entering the retry
loop
+// at all, which means those clients are waiting simultaneously by
construction:
+// they re-check the lock in lockstep, and each round of CheckLock calls
arrives
+// at the metastore as a burst. Spreading the wait decorrelates them.
+//
+// The jitter is added rather than subtracted so that the result is never
shorter
+// than the interval calculateBackoff produced. That keeps the guarantee
implied
+// by the lock-check-min-wait-time property: a caller who configures a minimum
+// wait never polls sooner than it.
+//
+// Once the backoff saturates at maxWait there is no headroom left to add into.
+// calculateBackoff reaches that point deliberately, so leaving it unjittered
+// would put contending clients back in lockstep for every retry after the
+// sequence tops out. The wait is therefore spread downwards instead, floored
at
Review Comment:
Small doc nit: this says the downward spread is "floored at minWait", but
the code at line 211 floors at max(d/2, minWait) — so the real floor is d/2,
and minWait only takes over when it's larger than half the interval. Worth
rewording to "floored at half the interval, or at minWait when minWait exceeds
half" so a future reader doesn't assume the at-cap wait can fall all the way to
minWait when it can't.
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