SERVER-5357 - idle connection timeouts

Changes.md

@@ -21,6 +21,8 @@ you spot any mistakes.
 * Add new error codes up to MySQL 5.7.29
 * Fix early detection of bad callback to `connection.query`
 * Support Node.js 12.x #2211
+* Add `idleConnectionTimeout` to pool options
+* Add `connectionMinLimit` to pool options
 * Support Node.js 13.x
 * Support non-enumerable properties in object argument to `connection.query` #2253
 * Update `bignumber.js` to 9.0.0

Readme.md

@@ -462,6 +462,11 @@ constructor. In addition to those options pools accept a few extras:
 * `queueLimit`: The maximum number of connection requests the pool will queue
   before returning an error from `getConnection`. If set to `0`, there is no
   limit to the number of queued connection requests. (Default: `0`)
+* `idleConnectionTimeout`: The maximum number of milliseconds a connection can be
+  idle in the pool. If set to `0` connection will live until it is manually
+  destroyed or the pool is closed. (Default: `0`)
+* `connectionMinLimit`: The minimum number of connections in the pool.
+  checked when removing a connection. (Default: `5`)
 
 ## Pool events
 

lib/Pool.js

@@ -106,6 +106,11 @@ Pool.prototype.acquireConnection = function acquireConnection(connection, cb) {
       pool.emit('connection', connection);
     }
 
+    if (connection._idleTimeout) {
+      clearTimeout(connection._idleTimeout);
+      connection._idleTimeout = null;
+    }
+
     pool.emit('acquire', connection);
     cb(null, connection);
   }

lib/PoolConfig.js

@@ -17,9 +17,17 @@ function PoolConfig(options) {
   this.connectionLimit    = (options.connectionLimit === undefined)
     ? 10
     : Number(options.connectionLimit);
+  //SERVER-5357 BEGIN
+  this.connectionMinLimit    = (options.connectionMinLimit === undefined)
+    ? 5
+    : Number(options.connectionMinLimit);
+  //SERVER-5357 END
   this.queueLimit         = (options.queueLimit === undefined)
     ? 0
     : Number(options.queueLimit);
+  this.idleConnectionTimeout         = (options.idleConnectionTimeout === undefined)
+    ? 0
+    : Number(options.idleConnectionTimeout);
 }
 
 PoolConfig.prototype.newConnectionConfig = function newConnectionConfig() {

lib/PoolConnection.js

@@ -5,6 +5,8 @@ var Events     = require('events');
 module.exports = PoolConnection;
 inherits(PoolConnection, Connection);
 
+function _noop() {}
+
 function PoolConnection(pool, options) {
   Connection.call(this, options);
   this._pool  = pool;
@@ -32,6 +34,13 @@ PoolConnection.prototype.release = function release() {
     return undefined;
   }
 
+  if (this._pool.config.idleConnectionTimeout) {
+    this._idleTimeout = setTimeout(
+      this._realEnd.bind(this, _noop),
+      this._pool.config.idleConnectionTimeout
+    );
+  }
+
   return pool.releaseConnection(this);
 };
 
@@ -58,6 +67,17 @@ PoolConnection.prototype._removeFromPool = function _removeFromPool() {
     return;
   }
 
+  if (this._idleTimeout) {
+    clearTimeout(this._idleTimeout);
+    this._idleTimeout = null;
+  }
+
+  //SERVER-5357 BEGIN
+  if (this._allConnections.length <= this.config.connectionMinLimit) {
+    return;
+  }
+  //SERVER-5357 END
+
   var pool = this._pool;
   this._pool = null;