perf: speed up RepositoryAdmin changelist search

[thomasrockhu-codecov]

Summary

The Django admin Repository changelist search is the #2 most expensive admin page in Sentry (/core/repository/, p95 ~73s). Its search ORed search_fields across the repos ⟷ owners join; because author__username is on a different table, Postgres can't use per-table indexes for that OR and falls back to a full parallel seq-scan + hash join.

This PR rewrites RepositoryAdmin.get_search_results to keep the filter single-table:

• Resolve author username → ownerids with one indexed query on owners, then filter repos with a single-table OR so each branch uses its own index (repos_name_trgm_idx trigram, service_id, ownerid, pk) via a BitmapOr.
• Require a 3-char minimum for substring name search (pg_trgm can only use the GIN trigram index for ≥3-char terms).
• Add list_select_related = ("author",) to remove the per-row author N+1 on the unsearched changelist.

No schema/migration change — the existing repos_name_trgm_idx is reused.

Measured impact

Local EXPLAIN (ANALYZE) against ~24.6M seeded repos:

Query	Before	After
name search (repo-500)	4,425 ms (seq scan + hash join)	34 ms (BitmapOr)
username search	full join scan	1.9 ms
2-char term	full join scan	0.03 ms (name skipped, index scan)

Behavior change

Substring name search now requires ≥3 characters; shorter terms still match service_id / username / repoid exactly.

Test plan

• Existing core/tests/test_admin.py::get_search_results tests pass
• EXPLAIN ANALYZE confirms BitmapOr / no seq scan for name, username, service_id, repoid searches
• Verify results parity in staging admin (name substring, username, service_id, repoid)
• Watch Sentry /core/repository/ p95 after deploy

Made with Cursor

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.88%. Comparing base (701e991) to head (27427d6).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/codecov-api/core/admin.py	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1417      +/-   ##
==========================================
- Coverage   91.89%   91.88%   -0.01%     
==========================================
  Files        1325     1325              
  Lines       50868    50875       +7     
  Branches     1626     1626              
==========================================
+ Hits        46744    46749       +5     
- Misses       3818     3820       +2     
  Partials      306      306              

Flag	Coverage Δ
apiunit	94.93% <87.50%> (-0.01%)	⬇️

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Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/codecov-api/core/admin.py	87.50%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (87.50%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

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