Open one connection per database instead of one per query

[vyruss]

Summary

Follows the review on #10: every per-database task opened its own connection. There are 46 per-database queries, so an archive from an eight-database instance cost 369 connect and authentication cycles.

The connection is now opened once per database and shared by that database's tasks, and closed when collection moves on, so only one is ever held. The task generator returns the closer that releases the last one. The database radar was invoked against reuses the connection opened at startup. The same eight-database instance now costs 8.

test-radar.sh reads pg_stat_database.sessions around the first scenario and fails above 10; the container's two databases report 2.

Checklist

• Unit tests (one connection per database, the startup connection reused for its own database, the previous one closed as collection moves on, the last one on the closer)
• Regression tests (go test ./... passes)
• Docs/README updated (connection count under Performance)
• Integration test impact (test-radar.sh asserts the session count; all 6 scenarios pass)
• Security checks (no change to what is collected)
• PR links to a tracking issue/ticket (none for this work)

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📝 Walkthrough

Walkthrough

The collector now reuses one connection per database and closes shared connections after collection. Tests verify connection reuse and cleanup. Integration documentation and scripts now cover six authentication scenarios and validate session counts.

Changes

Database connection reuse

Layer / File(s)	Summary
Shared connection lifecycle postgres.go, postgres_test.go, radar.go, radar_test.go	dbConns reuses one connection per database, switches connections when needed, and closes them after collection. Tests verify reuse, switching, and idempotent cleanup.

Integration test coverage

Layer / File(s)	Summary
Authentication scenarios and session validation test-radar.sh, CONTRIBUTING.md	The integration suite now defines six scenarios, including certificate and GSSAPI/Kerberos authentication. Scenario 1 validates that a radar run opens at most 10 sessions. Documentation updates expected collector counts and test requirements.

Performance documentation

Layer / File(s)	Summary
Connection reuse documentation README.md, docs/index.md	The performance documentation states that each database uses one reusable connection for all queries.

Poem

A rabbit watched the connections flow
One per database, steady and low
Six test paths crossed the meadow bright
Certificates gleamed in moonlit light
Kerberos hopped through the night
And every session count stayed right

Merge Risk: 🔵 Low · up to a9be2

When collection returns to the configured startup database after another database, the previous connection can remain open temporarily, holding an extra database session and weakening the intended connection reduction. The PR is mergeable with explicit owner follow-up to close the cached connection before returning the startup connection.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: reusing one database connection instead of opening one connection per query.
Description check	✅ Passed	The description directly explains the connection reuse change, connection lifecycle, tests, documentation updates, and integration test changes.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 5 files. (3 skipped: 3…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 5 files. (3 skipped: 3 unsupported.)

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Up to standards ✅

🟢 Issues 0 issues

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🟢 Metrics 0 duplication

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Actionable comments posted: 1

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Inline comments:
In `@postgres.go`:
- Around line 189-190: Update the cached-connection reuse branch around
cfg.Database and cfg.DB so the existing c.db connection is closed before
returning cfg.DB when switching from another database. Preserve the current
return behavior and avoid closing the connection when it is already the cached
cfg.DB instance.

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📥 Commits

Reviewing files that changed from the base of the PR and between a7f6a60 and a9be212.

📒 Files selected for processing (8)

• CONTRIBUTING.md
• README.md
• docs/index.md
• postgres.go
• postgres_test.go
• radar.go
• radar_test.go
• test-radar.sh

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[bonesmoses]

I made a comment, but it's not critical. Feel free to roll with what's here.