MaxGekk commented on code in PR #56848:
URL: https://github.com/apache/spark/pull/56848#discussion_r3490150016
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala:
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@@ -1287,3 +1298,60 @@ object DateTimeUtils extends SparkDateTimeUtils {
c
}
}
+
+/**
+ * Per-task memoization of a zone's UTC offset, used by the
[[DateTimeUtils.truncTimestamp]] hot
+ * path. The session zone is constant for a query and the offset is
piecewise-constant between DST
+ * transitions, so consecutive rows almost always resolve to the same offset.
The cache holds the
+ * half-open epoch-second interval `[lo, hi)` on which the offset is provably
constant -- derived
+ * from the surrounding zone transitions -- so a lookup that falls in the
interval reduces to two
+ * comparisons instead of a transition-array binary search.
+ *
+ * Not thread-safe by design: a fresh instance is created per task (codegen
mutable state) and used
+ * single-threaded, mirroring how stateful per-row helpers are scoped in
generated code.
+ */
+class ZoneOffsetCache(val zoneId: ZoneId) {
Review Comment:
Nice optimization, and the `hi-1` anchoring to dodge the on-transition
off-by-one is well reasoned. One gap: `ZoneOffsetCache` has no direct unit
test. The existing `DateTimeUtilsSuite` truncation tests all go through the
one-shot `truncTimestamp(micros, level, zoneId)` overload, which builds a
*fresh* cache per call — so they confirm the offset *values* near DST
transitions, but never exercise (a) the persistent cross-row reuse the codegen
per-task cache depends on, nor (b) the on-transition interval boundary directly
(the subtle part).
Since the class is public, a small focused test would lock in the reasoning:
consecutive `offsetSeconds` lookups within one window (hit), a lookup
straddling a transition (miss + window reset), and a lookup with `epochSec`
exactly on a transition instant (the `hi-1` anchor). Non-blocking.
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