feat: Set default values for DB connection parameters

- Configures `max_open` and `max_idle` in default configs to `25`.
  This changes the previous behaviour of connection pooling where both the
  values were unset (from default config) and causes unbounded connection
  limit and no connection reuse.
- Configures `db.SetConnMaxLifetime` which sets the maximum time the
  connection can be reused in a pool.
- Sets `max_conn_lifetime` in default config as `5 minutes`.

Closes https://github.com/knadh/listmonk/issues/225

cmd/queries.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"time"
 
 	"github.com/jmoiron/sqlx"
 	"github.com/lib/pq"
@@ -92,6 +93,7 @@ type dbConf struct {
 	SSLMode     string        `koanf:"ssl_mode"`
 	MaxOpen     int           `koanf:"max_open"`
 	MaxIdle     int           `koanf:"max_idle"`
+	MaxLifetime time.Duration `koanf:"max_lifetime"`
 }
 
 // connectDB initializes a database connection.
@@ -104,6 +106,7 @@ func connectDB(c dbConf) (*sqlx.DB, error) {
 	}
 	db.SetMaxOpenConns(c.MaxOpen)
 	db.SetMaxIdleConns(c.MaxIdle)
+	db.SetConnMaxLifetime(c.MaxLifetime)
 	return db, nil
 }
 

config-demo.toml

@@ -10,3 +10,6 @@
     password = "listmonk"
     database = "listmonk"
     ssl_mode = "disable"
+    max_open = 25
+    max_idle = 25
+    max_lifetime = "300s"

config.toml.sample

@@ -17,3 +17,6 @@
     password = "listmonk"
     database = "listmonk"
     ssl_mode = "disable"
+    max_open = 25
+    max_idle = 25
+    max_lifetime = "300s"