feat(quaint): expose pool health check options as connection string parameters

[YuzuruS]

Overview

The pooled Builder has long supported test_on_check_out and health_check_interval, and QuaintManager::check is already implemented as a SELECT 1 ping — but no connector URL parser exposes either option. Since Prisma builds its pool exclusively from the datasource URL via Quaint::builder_with_tracing, the health-check machinery is effectively dead code for Prisma users.

This PR makes both options parseable from the connection string for PostgreSQL, MySQL and SQL Server, following the exact pattern of the existing max_connection_lifetime / max_idle_connection_lifetime parameters.

New parameters

Parameter	Type	Default	Behavior
test_on_check_out	bool	false	When true, a connection is verified with SELECT 1 before being handed out of the pool. A connection that was silently severed while idle (NAT/LB idle timeout, server-side reset) is discarded and transparently replaced instead of failing the query with a connection error.
health_check_interval	seconds	none	Only meaningful with test_on_check_out=true: rate-limits the check to at most once per interval per connection (mobc marks the connection checked). 0 or omitted = verify every checkout.

SQL Server also accepts testOnCheckOut / healthCheckInterval, consistent with its other JDBC-style parameters (keys are case-normalized by the JDBC parser).

SQLite is intentionally excluded: an embedded file database has no network path that can go stale.

Why

Long-running deployments (ECS/Fargate, EC2, Kubernetes) hold pooled connections long enough for middleboxes or the server to sever them while idle. The next checkout hands out a dead connection and the query fails with an intermittent, hard-to-reproduce P1001/P1017 — the recurring theme behind reports like prisma/prisma#13770. Borrow-time validation is the standard remedy in every mainstream pool (HikariCP connectionTestQuery, pgbouncer server_check_query, tarn/knex afterCreate validation, etc.); quaint already has the mechanism, it just cannot be switched on.

Companion issue with a fully-correlated production trace (app logs + RDS system_health Extended Events): prisma/prisma#29786

Changes

• quaint/src/connector/postgres/url.rs — parse both params + getters
• quaint/src/connector/mysql/url.rs — parse both params + getters
• quaint/src/connector/mssql/url.rs — parse both params (camelCase + snake_case) + getters
• quaint/src/pooled.rs — wire both params into the Builder in builder_with_tracing for the three connectors; document the parameters in the module docs

No behavior change for existing connection strings (both options default to off; Builder defaults are untouched).

Testing

• 10 new unit tests covering: parse with values, defaults (disabled), 0 interval normalization, and mssql camelCase/snake_case spellings
  • cargo test -p quaint --features "pooled,all-native" --lib health_check → 10 passed
• cargo clippy -p quaint --features "pooled,all-native" → no warnings
• cargo fmt clean

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 3ed1dc2b-05e7-4c31-ba06-95bb9f9fc4c1

📥 Commits

Reviewing files that changed from the base of the PR and between 059a7b2 and d0b751a.

📒 Files selected for processing (4)

• quaint/src/connector/mssql/url.rs
• quaint/src/connector/mysql/url.rs
• quaint/src/connector/postgres/url.rs
• quaint/src/pooled.rs

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Summary by CodeRabbit

• New Features

  • Added connection-pool health-check configuration for MySQL, PostgreSQL, and Microsoft SQL Server.
  • Connection strings can now enable health checks when connections are checked out and set a health-check interval.
  • A zero or omitted interval disables periodic health checks, preserving existing defaults.

• Documentation

  • Documented the new connection parameters and their behavior.

Walkthrough

MySQL, PostgreSQL, and MSSQL connection URL parsers now support checkout testing and health-check interval parameters. The settings default to disabled, with a zero interval represented as no interval. New accessors expose the parsed values. Pool builder construction reads these settings for the three connectors and applies them, while pooled connection documentation describes the parameters and SQLite limitation. Tests cover provided values, defaults, and zero-interval behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: exposing pool health check options via connection string parameters.
Description check	✅ Passed	The description accurately describes the implemented URL parsing, builder wiring, connector coverage, and tests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

✨ Simplify code

• Create PR with simplified code

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