MaxConnectionPoolSize is not respected under heavy load

The default internal connection pool size for this driver seems to be set at 100. I’m seeing that this can be broken. Basic test to reproduce this behavior:

    test('Connection pool', async () => {
        const driver = Neo4J.driver('bolt://localhost:7687', Neo4J.auth.basic('neo4j', 'neo4j'), {
            disableLosslessIntegers: true,
        });

        const p: Promise<any>[] = [];
        for (let i = 0; i < 1500; i++) {
            p.push(new Promise(async (res, rej) => {
                const session = driver.session();
                await session.run('MATCH (n) RETURN n');
                session.close();
                res();
            }));
        }

        await Promise.all(p);
    }, 30000);

Watch netstat while you run this test and see that the number of connections goes into the thousands:

watch -n .5 'netstat -an | grep "7687" | grep ESTABLISHED | wc -l'

I’ve tested this against Neo4j 3.5.3 and 3.5.12 using driver versions 1.7.5 and 4.0.0-beta01.

[zhenlineo]

Hi @aaronjwood, The change was also merged in 1.7. But I currently do not have a patch release date for next 1.7. I will let you know once I got more information.

[zhenlineo]

Hi @aaronjwood , Thanks very much for reporting this to us. We are releasing a new 4.0.0-rc1 driver with the fix inside. The fix ensures the maximum active connection count is always less or equal to MaxConnectionPoolSize.