PoolConnection leaked by MysqlDriver.js

[DillonSadofsky]

Issue Description

Using the current version of TypeORM (0.3.3), I noticed if I set my MySQL connection pool to a particularly small size, my app would lock up on attempting to get the first exclusive connection via QueryRunner.connect(). I poked around and stepped through the MysqlDriver code and I believe this is because on line 306 of MysqlDriver.js there is the line:

        const result = (await this.createQueryRunner("master").query(`SELECT VERSION() AS \`version\``));

It appears to want to run the version query to know whether certain features are available, but the queryrunner that is created here never releases back into the pool, which eats up a connection until the server shuts down.

Inlining QueryRunner.query() like this implicitly calls connect() on line 145 of MysqlQueryRunner.js but it is never released.

As documented here: https://github.com/typeorm/typeorm/blob/master/docs/query-runner.md
a query runner that gets connected needs to be explicitly released after we're done.

createQueryRunner("master") is called several other times in MysqlDriver.js but it seems like the connection is released correctly in the other areas.

Expected Behavior

If a connection is implicitly pulled from the query pool by any driver overhead, it should be released back into the pool or terminated so that the pool can reallocate that connection later.

Actual Behavior

One connection is pulled from the pool and never released back.

Steps to Reproduce

Create a typeorm project, establish a mysql connection pool of size 1, and then attempt to retrieve an exclusive connection from the pool using the following code:

		const connection = pool.createQueryRunner()
		const rawConnection = await connection.connect() as mysql.PoolConnection

My Environment

typeorm .3.3

Relevant Database Driver(s)

DB Type	Reproducible
aurora-mysql	no
aurora-postgres	no
better-sqlite3	no
cockroachdb	no
cordova	no
expo	no
mongodb	no
mysql	yes
nativescript	no
oracle	no
postgres	no
react-native	no
sap	no
sqlite	no
sqlite-abstract	no
sqljs	no
sqlserver	no

Are you willing to resolve this issue by submitting a Pull Request?

• ✖️Yes, I have the time, and I know how to start.
• ✖️ Yes, I have the time, but I don't know how to start. I would need guidance.
• ✖️ No, I don’t have the time, but I can support (using donations) development.
• ✅ No, I don’t have the time and I’m okay to wait for the community / maintainers to resolve this issue.

[DillonSadofsky]

I did a quick test and changed that line in MysqlDriver.js to:

		const queryRunner = await this.createQueryRunner("master");
		const result = await queryRunner.query(`SELECT VERSION() AS \`version\``);
		await queryRunner.release();
		const dbVersion = result[0].version;

And it seemed like it fixed it, but I'm not super familiar with the internals, so I'll leave it to others to review.

[MonkeysFletch]

@DillonSadofsky Glad you figured this out. Upgrading to 0.3.3 from 0.2.x had my single connection Lambdas hanging. Upping them to 2 connections in the settings allowed them to succeed for the time being.

Here's my relevant information if it helps anyone out with confirming/fixing:

export class Database {
    private source: DataSource;

    constructor(options?: DeepPartial<DataSourceOptions>) {
        let defaultOptions: DataSourceOptions = {
            type: "mysql",
            host: process.env.DB_HOST,
            port: 3306,
            username: process.env.DB_USER,
            password: process.env.DB_PASS,
            database: process.env.DB_NAME,
            connectTimeout: 20000,
            acquireTimeout: 20000,
            synchronize: true,
            logging: "all",
            entities: [
                ...
            ],
            extra: {
                connectionLimit: 1,
            },
        };
        if (options) _.merge(defaultOptions, options)
        this.source = new DataSource(defaultOptions)
    }

    public async getConnection(): Promise<DataSource> {
        const connection = this.source.initialize();
        return connection;
    } 
}

const database = new Database();
let connection = database.getConnection();

const Handler: ValidatedEventAPIGatewayProxyEvent<typeof schema> = async (event, context) => {
    context.callbackWaitsForEmptyEventLoop = false;
    try {
        const connected = await connection;
        // DB stuff here
    
    } catch (err){
        // Error handling
    }
}

I was able to log all the way up to connected, and then it hangs on the same single query followed by a Lambda timeout and failure:

INFO	query: SELECT VERSION() AS `version`

[pleerock]

looks like bug was introduced in #8673