Configuration

Generated rustdoc: https://docs.rs/babar/latest/babar/struct.Config.html

See also: Book Chapter 1 — Connecting, Chapter 6 — Pooling, Chapter 12 — TLS & security.

`babar::Config`

Config holds everything Session::connect needs. Required fields are positional in the constructor; optional fields are chained methods. Build it from any source — env vars, a config file, a clap::Parser. babar deliberately doesn’t ship a DSN parser.

Constructors

Method	Required arguments
`Config::new(host, port, user, dbname)`	`impl Into<String>` for host/user/dbname, `u16` for port. Resolves `host` via DNS at connect time.
`Config::with_addr(addr, port, user, dbname)`	`addr: IpAddr`, `port: u16`, `user`/`dbname` as `impl Into<String>`. Skips DNS — useful for IP-direct deployments.

Optional fields (chained, value-returning)

Method	Type	Default	Notes
`.password(p)`	`impl Into<String>`	none	Sent to the server only as part of the auth handshake.
`.application_name(n)`	`impl Into<String>`	none	Surfaces in `pg_stat_activity.application_name`. Cheapest observability win.
`.connect_timeout(d)`	`Duration`	none	Wall-clock cap on `Session::connect`.
`.tls_mode(m)`	`TlsMode`	`Disable`	`Disable` / `Prefer` / `Require`. Opt in to `Prefer` or `Require` explicitly. See ch12.
`.require_tls()`	—	—	Sugar for `.tls_mode(TlsMode::Require)`.
`.tls_backend(b)`	`TlsBackend`	`Rustls` (with `rustls` feature)	`Rustls` or `NativeTls`.
`.tls_server_name(n)`	`impl Into<String>`	host	Override SNI / certificate-name match.
`.tls_root_cert_path(p)`	`impl Into<PathBuf>`	system roots / `webpki-roots`	PEM bundle of additional root CAs.

TLS-mode and backend enums

Enum	Variants	Re-exported as
`TlsMode`	`Disable`, `Prefer`, `Require`	`babar::config::TlsMode`
`TlsBackend`	`Rustls`, `NativeTls`	`babar::config::TlsBackend`

`babar::PoolConfig`

PoolConfig is everything Pool::new needs that isn’t a Config.

Constructor

PoolConfig::new() — conservative defaults. All knobs are chained, value-returning methods.

Knobs

Method	Type	Default	Notes
`.min_idle(n)`	`usize`	`0`	Keep at least `n` warm connections when traffic permits.
`.max_size(n)`	`usize`	`16`	Hard cap on total connections in the pool.
`.acquire_timeout(d)`	`Duration`	30 seconds	How long `pool.acquire()` waits before returning `PoolError::Timeout`.
`.idle_timeout(d)`	`Duration`	unset (no idle timeout)	Close idle connections older than this.
`.max_lifetime(d)`	`Duration`	unset (no lifetime cap)	Recycle connections after this age regardless of idle state.
`.health_check(h)`	`HealthCheck`	`HealthCheck::None`	Per-acquire validation policy (off by default).

`PoolError`

Variant	When
`PoolError::Timeout`	`acquire_timeout` elapsed before a slot freed up.
`PoolError::AcquireFailed(babar::Error)`	The pool tried to open a fresh connection and the underlying `Session::connect` failed.
`PoolError::PoolClosed`	The pool itself has been closed.

Picking values

Some tested starting points:

Service shape	`max_size`	`acquire_timeout`	`min_idle`
HTTP service, low/medium traffic	`8`–`16`	`5–10s`	`0`
HTTP service, high traffic	`≈ #worker threads × 2`	`1–3s`	`≥ 2`
Long-running batch / ETL	`1`–`4`	`30s+`	`0`

Beyond that, watch:

pg_stat_activity for connection count vs server’s max_connections.
Pool acquire latency (you wrap it yourself; see Chapter 13).
p99 query latency vs pool size — if increasing max_size doesn’t move p99, the pool isn’t the bottleneck.

For the cargo features that gate TLS backends and codec types, see feature-flags.md. For the errors these knobs can produce, see errors.md.

The Book of Babar