bug: timezone mismatch by clickhouse and web

[hanjoo-kim-tossbank]

Describe the bug

I want to use the existing clickhouse in a custom timezone. If clickhouse's default timezone is set to the other than UTC, the langfuse UI describes wrong timestamp.

For example, the clickhouse is set to KST (UTC+9) and a certain trace was created at 01:00 in UTC.
Then the clickhouse stored that trace in 10:00 in KST by the default timezone setting.
Later, langfuse UI would fetch the trace from the clickhouse and its timestamp is translated into UTC, not KST. Finally, it applies local timezone in web client once again (19:00 in KST)

Steps to reproduce

1. Clickhouse setting: default time zone to KST
2. Langfuse web working on UTC timezone
3. Store traces in UTC
4. View in langfuse UI

Langfuse Cloud or self-hosted?

Self-hosted

If self-hosted, what version are you running?

3.140.0

SDK and integration versions

No response

Additional information

If the clickhouse client enables use_client_time_zone, the clickhouse server may return the traces with the timestamp in client timezone (UTC): https://github.com/ClickHouse/clickhouse-js/blob/8f2add94dc9e064d96b94dcb0dac019d7286e9c0/packages/client-common/src/settings.ts#L1555C3-L1555C23

Are you interested in contributing a fix for this bug?

Yes

[dosubot]

Hi @hanjoo-kim-tossbank! I'm Dosu and I’m helping the langfuse team.

Langfuse expects all infrastructure components—including ClickHouse—to use the UTC timezone. If ClickHouse is set to a non-UTC timezone (like KST), timestamps are stored and returned in that local time, but Langfuse always interprets them as UTC. This causes the UI to display incorrect times after the browser applies its own local timezone conversion, resulting in the drift you described. There is no built-in support or configuration in Langfuse to handle non-UTC ClickHouse timezones, and the codebase does not set or expose the ClickHouse use_client_time_zone setting by default. All timestamps from ClickHouse are parsed as if they are UTC, regardless of the server's actual timezone setting (docs, discussion).

Workarounds used by the community include: (1) changing ClickHouse table columns to use explicit UTC (e.g., DateTime64(3, 'UTC')), (2) ensuring all timestamps are generated and stored in UTC (even if the server's default timezone cannot be changed), and (3) patching SDKs or migration files to use UTC for all time-related fields. Attempts to add multi-timezone support (e.g., via a CLICKHOUSE_USE_LOCAL_TIMEZONE env var) have been declined by maintainers due to the complexity and risk of breaking existing deployments (PR).

The best practice is to ensure ClickHouse and all related infrastructure run in UTC. If that's not possible, updating your schema and timestamp generation logic to always use UTC (regardless of server default) can resolve the issue. If you want to see official support for multi-timezone setups, you can vote and share your use case in the ongoing GitHub discussion.

To reply, just mention @dosu.

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[Steffen911]

@hanjoo-kim-tossbank I can confirm dosu's answer and the links that are provided. Having non-UTC timezones in any of the Langfuse components is currently not supported.