featzhang created FLINK-39042:
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Summary: [webui] Make watermark timestamps timezone-aware and
configurable
Key: FLINK-39042
URL: https://issues.apache.org/jira/browse/FLINK-39042
Project: Flink
Issue Type: Improvement
Components: Runtime / Web Frontend
Reporter: featzhang
h4. Summary
The Flink Web UI Watermarks page already supports displaying *formatted
datetime strings* for watermark timestamps.
However, the {*}timezone is neither explicitly indicated nor configurable{*},
which can easily lead to ambiguity and operational confusion in multi-region
environments.
This issue proposes to *explicitly label the timezone* used for formatted
timestamps and *add a timezone switching capability* to the UI.
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h4. Current Behavior
* The Watermarks page displays:
** Raw timestamp (milliseconds since epoch)
** A formatted datetime string (e.g. {{{}2026-02-05 09:58:50{}}})
* {*}Problems with the current behavior{*}:
## The formatted time {*}does not clearly indicate which timezone it belongs
to{*}.
## Users cannot switch the timezone (e.g. UTC vs local time).
## Operators must _infer_ the timezone based on browser or deployment context,
which is error-prone.
Example (current UI):
{{1770256730000 → 2026-02-05 09:58:50}}
>From this display alone, it is unclear whether the time is UTC, browser local
>time, or another timezone.
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h4. Proposed Improvements
h5. 1. Explicit Timezone Labeling
* Always display the timezone together with the formatted timestamp.
* Suggested format:
{{Timestamp (YYYY-MM-DD HH:mm:ss Z)}}
Example:
{{1770256730000 (2026-02-05 09:58:50 UTC+8)}}
This removes ambiguity and makes the time semantics explicit.
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h5. 2. Timezone Switching Support
* Add a timezone selector (e.g. dropdown or toggle group) above the Watermarks
table.
* Supported options could include:
** UTC
** Browser Local Time
** Fixed offsets (e.g. UTC+8)
Example UI concept:
{{[ Timezone: UTC | Local | UTC+8 ]}}
Changing the selection updates all formatted timestamps on the page accordingly.
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h5. 3. Consistency & Reusability
* The same timezone formatting and switching logic should be reusable for:
** Checkpoints
** Backpressure
** Other Web UI pages displaying time-based metrics
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h4. Motivation & Use Cases
* *Debugging*
Quickly determine whether a subtask watermark is lagging behind wall-clock time
without guessing the timezone.
* *Monitoring & Operations*
Teams operating clusters across regions can view timestamps in a consistent,
explicit timezone.
* *User Experience*
Avoid confusion caused by implicit timezone assumptions.
----
h4. Non-Goals
* This issue does *not* change watermark semantics or calculation logic.
* This issue focuses purely on {*}UI presentation and usability
improvements{*}.
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