Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

Bar chart: bars on a temporal x-axis shrink to hairlines when the time grain is finer than the data (7.0.0rc2)

Open Beginner friendly
  • Is something wrong?
#45,474 0 comments 0 reactions 0 assignees View on GitHub

Maintainers usually reply within 2 days

@Anikesh0001 is already working on this.

Since Oct 20, 2026.

  • #45519 by @Anikesh0001 — open

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
react, typescript
Domain
data-visualization, frontend

Research direction

Start in superset-frontend/plugins/plugin-chart-echarts/src/utils/series.ts at getGrainBarMaxWidth, then read its callers in Timeseries/transformProps.ts and MixedTimeseries/transformProps.ts. Review test/Timeseries/Bar/sparseSubDailyBarGeometry.test.ts and add coverage for Day grain with monthly and yearly data in both chart types. Done when those cases keep the fallback bar width while the existing sub-daily behavior remains covered.

Written by the indexing model from the issue text.

Description

#bug 🦾 ai-candidate
Bug description

(I used Claude AI to assist in writing up an error I encountered - I have read and edited this)

In 7.0.0rc2, a Bar Chart with a temporal x-axis draws its bars about 1px wide when the time grain is finer than the spacing of the data. The common case is the default grain, Day, on data that is already monthly or yearly. In 6.1.0 the same saved chart draws normal-width bars.

Our case is a stacked bar chart with one bar per year. The x-axis column Year holds 2019-01-01 00:00:00, 2020-01-01 00:00:00, …, 2024-01-01 00:00:00. The time grain is the default, Day. In 6.1.0 each bar fills most of the gap between years. In 7.0.0rc2 each bar is a sliver less than 1px wide.

The cause is getGrainBarMaxWidth in superset-frontend/plugins/plugin-chart-echarts/src/utils/series.ts, added by #44628. It sets the bar series' barMaxWidth to the width of one grain bucket:

const domainSpanMs =
  domainMax > domainMin ? domainMax - domainMin : 2 * ONE_DAY_MS;
return (grainMs / domainSpanMs) * Math.max(plotLengthPx, 0);

For our chart:

  • Grain: Day, so 1 day
  • Data span: 2019-01-01 to 2024-01-01, about 1,826 days
  • Plot width: about 750px
  • Result: 750 × 1/1826 ≈ 0.4px

Before #44628, ECharts sized bars on a time axis from the actual gap between data points (one year here), with barMaxWidth: 100 as the cap. The grain didn't affect bar width.

#44628 was meant for sparse sub-daily data, and the comment it added in Timeseries/transformers.ts says so: "For a sub-daily time grain, transformProps.ts overrides this with a grain-derived value". The code doesn't match that comment, though. getGrainBarMaxWidth applies to every grain in TIMEGRAIN_TO_TIMESTAMP, which includes Day, Month, Quarter and Year. The PR's tests in test/Timeseries/Bar/sparseSubDailyBarGeometry.test.ts all use PT1H, so nothing tests the Day-and-coarser cases.

Day is the default for time_grain_sqla, so any saved bar chart of pre-aggregated monthly or yearly data that kept the default will show hairline bars after upgrading. The override runs in MixedTimeseries/transformProps.ts too, so mixed charts with a bar series are affected the same way.

Choosing a coarser grain works around it for our chart, but that isn't a general fix. The grain also truncates the date column in SQL. Data stamped on fiscal-year starts (e.g. July 1) would be moved and possibly merged by a Year grain. Irregularly spaced dates have no grain that fits.

How to reproduce

  1. Use a dataset with a temporal column holding one value per year (or per month), e.g. 2019-01-01 through 2024-01-01, and a numeric metric.
  2. Create a Bar Chart with that column as the x-axis. Leave Time Grain at the default, Day. Stacking makes no difference.
  3. The bars are drawn as hairlines.
  4. Change Time Grain to Year (or Month for monthly data). The bars are normal width again.

Expected behavior

As in 6.1.0, bars on pre-aggregated data are sized from the spacing of the data whatever the grain setting, so a Day grain on yearly data draws wide bars.

Proposed fix

Apply the grain-based override only to sub-daily grains, as #44628's title and comment describe. In getGrainBarMaxWidth, return undefined (keeping the existing barMaxWidth: 100 fallback and ECharts' own sizing) when the grain is a day or longer:

if (!grainMs || grainMs >= ONE_DAY_MS) {
  return undefined;
}

This brings back 6.1.0 behavior for Day and coarser grains and keeps the #44628 fix for the sparse hourly and minute data it targeted. The existing PT1H tests should still pass.

Unit tests should cover a Day grain on yearly and monthly data, checking that barMaxWidth stays at the fallback, in both Timeseries and MixedTimeseries.

I also considered sizing by the larger of the grain and the smallest observed gap between points. That would partly undo #44628, because a gap-sized bar is what spilled across empty buckets in the original sparse sub-daily bug.

Screenshots/recordings

6.1.0 (expected):
Image

7.0.0rc2 (regression), same saved chart:
Image

Chart config (x-axis Year, Time Grain: Day):
Image

Superset version

7.0.0rc2

Checklist
  • I have searched Superset docs and Slack and didn't find a solution to my problem.
  • I have searched the GitHub issue tracker and didn't find a similar bug report.
  • I have checked Superset's logs for errors and if I found a relevant Python stacktrace, I included it here as text in the "additional context" section.
Dominant language
Python
Stars
75.2k
Forks
18.5k
Avg merge
2d 20h
Merged PRs (30d)
649

Getting set up

Open in Codespaces

Starts the project's dev container in your browser, under your own GitHub account.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from apache/superset

All issues in apache/superset

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.