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Use LIFO for returning/retrieving connections from the pool #2085

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6 changes: 4 additions & 2 deletions Readme.md
Original file line number Diff line number Diff line change
Expand Up @@ -367,8 +367,10 @@ time one is needed.

Connections are lazily created by the pool. If you configure the pool to allow
up to 100 connections, but only ever use 5 simultaneously, only 5 connections
will be made. Connections are also cycled round-robin style, with connections
being taken from the top of the pool and returning to the bottom.
will be made. Connections are cycled on a last in first out basis, with connections
being taken from the top and returning to the top of the pool. This allows for
connections to be killed off by the server due to inactivity after `wait_timeout`
for the connection has been reached.

When a previous connection is retrieved from the pool, a ping packet is sent
to the server to check if the connection is still good.
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4 changes: 2 additions & 2 deletions lib/Pool.js
Original file line number Diff line number Diff line change
Expand Up @@ -137,8 +137,8 @@ Pool.prototype.releaseConnection = function releaseConnection(connection) {
// this won't catch all double-release cases
throw new Error('Connection already released');
} else {
// add connection to end of free queue
this._freeConnections.push(connection);
// add connection to front of free queue
this._freeConnections.unshift(connection);
this.emit('release', connection);
}
}
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45 changes: 45 additions & 0 deletions test/unit/pool/test-connection-cycling.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
var after = require('after');
var assert = require('assert');
var common = require('../../common');
var pool = common.createPool({port: common.fakeServerPort});

var server = common.createFakeServer();
var lastConnectionId = null;
var numberOfConnections = 4;

server.listen(common.fakeServerPort, function (err) {
assert.ifError(err);

var getConnectionAndEnsureItsTheLastConnection = function(cb) {
pool.getConnection(function (err, connection) {
assert.ifError(err);
assert.ok(connection.id === lastConnectionId);
connection.release();
if (cb) cb();
});
};

var done = after(numberOfConnections, function () {
getConnectionAndEnsureItsTheLastConnection(function() {
getConnectionAndEnsureItsTheLastConnection(function() {
pool.end(function (err) {
assert.ifError(err);
server.destroy();
});
});
});
});

var counter = 1;

var createIndexedConnection = function () {
pool.getConnection(function (err, connection) {
connection.id = counter++;
lastConnectionId = connection.id;
assert.ifError(err);
connection.release();
done();
});
};
Array.apply(null, {length: numberOfConnections}).map(createIndexedConnection);
});