fix: protect publish path from mysql exhaustion

server/db/mysql/adapter.go

@@ -21,6 +21,7 @@ import (
 	"github.com/tinode/chat/server/auth"
 	dbadapter "github.com/tinode/chat/server/db"
 	"github.com/tinode/chat/server/db/common"
+	immetrics "github.com/tinode/chat/server/metrics"
 	"github.com/tinode/chat/server/store"
 	t "github.com/tinode/chat/server/store/types"
 )
@@ -109,6 +110,9 @@ type configType struct {
 	MaxOpenConns int `json:"max_open_conns,omitempty"`
 	// Maximum number of connections in the idle connection pool.
 	MaxIdleConns int `json:"max_idle_conns,omitempty"`
+	// Registry database has a separate, much smaller workload and pool budget.
+	RegistryMaxOpenConns int `json:"registry_max_open_conns,omitempty"`
+	RegistryMaxIdleConns int `json:"registry_max_idle_conns,omitempty"`
 	// Maximum amount of time a connection may be reused (in seconds).
 	ConnMaxLifetime int `json:"conn_max_lifetime,omitempty"`
 
@@ -185,6 +189,7 @@ func openMySQLDB(config configType, dsn, dbName string) (*sqlx.DB, string, error
 	if config.ConnMaxLifetime > 0 {
 		db.SetConnMaxLifetime(time.Duration(config.ConnMaxLifetime) * time.Second)
 	}
+	immetrics.RegisterDBPool(dbName, db.DB)
 	return db, dbName, nil
 }
 
@@ -281,7 +286,14 @@ func (a *adapter) Open(jsonconfig json.RawMessage) error {
 			a.txTimeout = time.Duration(float64(config.SqlTimeout)*txTimeoutMultiplier) * time.Second
 		}
 		if a.tenantRegistryDB != "" && a.tenantRegistryDB != a.dbName {
-			a.registryDB, _, err = openMySQLDB(config, a.dsn, a.tenantRegistryDB)
+			registryConfig := config
+			if config.RegistryMaxOpenConns > 0 {
+				registryConfig.MaxOpenConns = config.RegistryMaxOpenConns
+			}
+			if config.RegistryMaxIdleConns > 0 {
+				registryConfig.MaxIdleConns = config.RegistryMaxIdleConns
+			}
+			a.registryDB, _, err = openMySQLDB(registryConfig, a.dsn, a.tenantRegistryDB)
 			if err == nil {
 				err = a.registryDB.Ping()
 			}