Cache ZoneId in ZonedDateTimeAdapter to reduce allocation pressure#34
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ZoneId.systemDefault() internally calls TimeZone.getDefault() which clones the ZoneInfo object on every invocation. Since parse() is called for every datetime field in SIRI XML messages, this creates significant allocation pressure. Cache the default ZoneId and ZoneOffset as static final constants to eliminate this per-call overhead.
lassetyr
approved these changes
Feb 27, 2026
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Summary
ZoneId.systemDefault()andZoneOffset.ofHours(0)asstatic finalconstants inZonedDateTimeAdapterinstead of calling them on everyparse()invocation.Motivation
JFR profiling of OTP2 with a live SIRI-ET feed showed that
ZonedDateTimeAdapter.parse()consumed 5.9% of total CPU during real-time processing. The root cause isZoneId.systemDefault(), which internally callsTimeZone.getDefault()— this clones theZoneInfoobject on every call. With thousands of datetime fields per SIRI message, this produced ~717 MB of sampledZoneInfoallocations and ~3.9 GB ofThreadLocalMap$Entryallocations over an 11-minute profiling window (~150 MB/s total allocation rate).Caching the
ZoneIdandZoneOffsetas class-level constants eliminates this per-call overhead entirely.Trade-off
By caching
ZoneId.systemDefault()at class load time, the default zone is resolved once and reused for the lifetime of the JVM. This means that any runtime changes to the default timezone (viaTimeZone.setDefault()orSystem.setProperty("user.timezone", ...)) will not be picked up byZonedDateTimeAdapter. In practice this is a non-issue for server applications like OTP where the timezone is set at startup and never changed, but it is a behavioural change worth noting.