fix(Segments): Restore segment list performance on large installations by matthewelwell · Pull Request #8587 · Flagsmith/flagsmith

matthewelwell · 2026-09-23T18:52:45Z

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Changes

Since #8548, get_all_live_or_scheduled_overrides compared a feature state's version against EnvironmentFeatureVersion.objects.get_live_or_scheduled() — an uncorrelated subquery over every published version in the installation. Correlating the check to the feature state's own feature and environment lets the existing efv_env_feature_pub_created index serve it, so there is no migration.

How did you test this code?

EXPLAIN (ANALYZE) on a production read replica, listing segments for a project with 156 of them.

Before — 59,069 ms. SubPlan 1 is the version check, reading ~90k and ~147k version rows, 313 times over. Note also features_featuresegment scanned by primary key, and features_featurestate gathered across the whole table:

Index Scan using segments_segment_project_id on segments_segment (actual time=526.402..59068.949 rows=156 loops=1)
  SubPlan 2
    ->  Merge Semi Join (actual time=378.375..378.396 rows=1 loops=156)
          ->  Index Scan using features_featuresegment_pkey (actual time=43.666..43.666 rows=1 loops=156)
                Filter: (segment_id = segments_segment.id)
                Rows Removed by Filter: 112198
          ->  Gather Merge (actual time=63.223..327.546 rows=98349 loops=156)
                ->  Nested Loop Left Join (actual time=0.091..219.699 rows=33110 loops=468)
                      ->  Parallel Index Scan using features_featurestate_feature_segment_id (rows=37767 loops=468)
                      SubPlan 1
                        ->  Merge Anti Join (actual time=0.108..156.984 rows=45721 loops=313)
                              ->  Index Scan using efv_env_feature_pub_created v0 (rows=90105 loops=313)
                              ->  Index Scan using efv_env_feature_pub_created u0 (rows=147469 loops=313)
Execution Time: 59069.494 ms

After — 3.6 ms. SubPlan 1 is now an index seek and is never reached; the other two joins flip to nested loops on the right indexes:

Limit (actual time=0.600..3.335 rows=156 loops=1)
  ->  Index Scan using segments_segment_project_id on segments_segment (rows=156 loops=1)
  SubPlan 2
    ->  Nested Loop Semi Join (actual time=0.018..0.018 rows=1 loops=156)
          ->  Index Scan using features_featuresegment_segment_id (actual time=0.004..0.004 rows=1 loops=156)
                Index Cond: (segment_id = segments_segment.id)
          ->  Nested Loop Left Join (actual time=0.013..0.013 rows=1 loops=156)
                ->  Index Scan using features_featurestate_feature_segment_id (rows=1 loops=156)
                      Index Cond: (feature_segment_id = w0.id)
                SubPlan 1
                  ->  Index Scan using efv_env_feature_pub_created (never executed)
                        Index Cond: ((environment_id = v0.environment_id) AND (feature_id = v0.feature_id))
Execution Time: 3.622 ms

The existing get_all_live_or_scheduled_overrides tests cover the semantics and pass unchanged. The new test asserts how many version rows the plan reads: 1 with this change, 4,002 without.

vercel · 2026-09-23T18:52:52Z

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coderabbitai · 2026-09-23T18:53:12Z

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📝 Walkthrough

Walkthrough

The v2 filter in get_all_live_or_scheduled_overrides now checks for a later published version of the same feature and environment whose live_from is no later than the current time. It excludes the current version when such a version exists. The v1 filtering path is unchanged.

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github-actions · 2026-09-23T18:53:54Z

Docker builds report

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codecov · 2026-09-23T18:58:48Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.80%. Comparing base (3e5fa33) to head (89534b8).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8587      +/-   ##
==========================================
- Coverage   98.81%   98.80%   -0.01%     
==========================================
  Files        1631     1631              
  Lines       67012    67013       +1     
==========================================
- Hits        66215    66214       -1     
- Misses        797      799       +2

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github-actions · 2026-09-23T19:00:10Z

✅ private-cloud · depot-ubuntu-latest-arm-16 — run #20766 (attempt 1)

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1 minute, 3 seconds
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18 seconds
89534b8
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✅ oss · depot-ubuntu-latest-16 — run #20766 (attempt 1)

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1 test across 1 suite
32.1 seconds
89534b8
🔄 Run: #20766 (attempt 1)

✅ oss · depot-ubuntu-latest-arm-16 — run #20766 (attempt 1)

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18 passed
1 skipped

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19 tests across 12 suites
1 minute, 8 seconds
89534b8
🔄 Run: #20766 (attempt 1)

Skipped tests

firefox › tests/onboarding-tests.pw.ts › Onboarding › New user connects via the single-page onboarding flow @oss

✅ private-cloud · depot-ubuntu-latest-arm-16 — run #20765 (attempt 1)

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38.5 seconds
b77585a
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✅ private-cloud · depot-ubuntu-latest-16 — run #20765 (attempt 1)

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3 passed

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33.4 seconds
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✅ oss · depot-ubuntu-latest-arm-16 — run #20765 (attempt 1)

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1 test across 1 suite
47.1 seconds
b77585a
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✅ oss · depot-ubuntu-latest-16 — run #20765 (attempt 1)

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34.8 seconds
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3 tests across 2 suites
12.2 seconds
53ae4aa
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✅ private-cloud · depot-ubuntu-latest-16 — run #20764 (attempt 1)

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39.6 seconds
53ae4aa
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✅ oss · depot-ubuntu-latest-16 — run #20764 (attempt 1)

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11.4 seconds
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4.4 seconds
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github-actions · 2026-09-23T19:01:13Z

Visual Regression

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`get_all_live_or_scheduled_overrides` matched a feature state's version against `EnvironmentFeatureVersion.objects.get_live_or_scheduled()`, an uncorrelated subquery over every published version in the installation. On a reported project, the `has_overrides` annotation on the segment list took 59 seconds to return 156 rows, almost all of it spent in a merge anti-join reading ~90k and ~147k version rows, 313 times over. Correlate the superseded-version check with the feature state's own feature and environment instead, which the existing `efv_env_feature_pub_created` index already covers. The same query then runs in 3.6ms, and the planner drops the merge joins that scanning drove it to, reading `features_featuresegment` by segment rather than by primary key. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

emyller

To be fair, I still don't grasp why the filter needs to be not superseded instead of superseding, but the logic here looks sound.

for more information, see https://pre-commit.ci

Drop the module-level constant and the helper's return value, and assert the exact number of version rows the plan reads rather than a fraction of the table's size. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

coderabbitai

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matthewelwell requested a review from a team as a code owner September 23, 2026 18:52

matthewelwell requested review from emyller and removed request for a team September 23, 2026 18:52

github-actions Bot added api Issue related to the REST API fix labels Sep 23, 2026

coderabbitai Bot reviewed Sep 23, 2026

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Comment thread api/tests/unit/segments/test_unit_segments_services.py Outdated

matthewelwell marked this pull request as draft September 23, 2026 19:00

matthewelwell force-pushed the fix(segments)/has-overrides-full-table-scan branch from 2f444dd to 07463d5 Compare September 23, 2026 20:43

emyller requested changes Sep 23, 2026

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Comment thread api/segments/services.py

Comment thread api/tests/unit/segments/test_unit_segments_services.py Outdated