Pool timeout error with minimumIdle = 0

[n0v1]

Hello there,

I noticed an unexpected behaviour in mariadb version 3.4.5: When setting minimumIdle to 0, queries fail with a pool timeout error after acquireTimeout is reached.

Reproduction:

const mariadb = require('mariadb')

const pool = mariadb.createPool({
  host           : 'localhost',
  port           : 3306,
  user           : 'test',
  password       : 'test',
  database       : 'test',
  minimumIdle    : 0,
  acquireTimeout : 5 * 1000,
})

const main = async () => {
  try {
    await pool.query('SELECT SLEEP(0.5)')
  } finally {
    await pool.end()
  }
}

main()
  .then(() => console.log('done'))
  .catch(err => console.error(err))

When not setting minimumIdle or when setting it to a positive value this works as expected but when setting it to 0, it logs this error:

SqlError: (conn:-1, no: 45028, SQLState: HY000) pool timeout: failed to retrieve a connection from pool after 5004ms
    (pool connections: active=0 idle=0 limit=10)
    at module.exports.createError (/home/me/test/node_modules/.pnpm/mariadb@3.4.5/node_modules/mariadb/lib/misc/errors.js:66:10)
    at Pool._rejectTimedOutRequest (/home/me/test/node_modules/.pnpm/mariadb@3.4.5/node_modules/mariadb/lib/pool.js:347:33)
    at Pool._checkRequestTimeouts (/home/me/test/node_modules/.pnpm/mariadb@3.4.5/node_modules/mariadb/lib/pool.js:315:14)
    at listOnTimeout (node:internal/timers:588:17)
    at process.processTimers (node:internal/timers:523:7) {
  sqlMessage: 'pool timeout: failed to retrieve a connection from pool after 5004ms\n' +
    '    (pool connections: active=0 idle=0 limit=10)',
  sql: null,
  fatal: false,
  errno: 45028,
  sqlState: 'HY000',
  code: 'ER_GET_CONNECTION_TIMEOUT'
}

Even with no idle connections auto-created on pool instanciation (minimumIdle: 0) I would expect the query to work.

I think this happens because of check this.#idleConnections.length < this.opts.minimumIdle in _shouldCreateMoreConnections() (see https://github.com/mariadb-corporation/mariadb-connector-nodejs/blob/3.4.5/lib/pool.js#L472). When changing the check to (this.#idleConnections.length < this.opts.minimumIdle) || this.opts.minimumIdle <= 0 it works fine.

Is this expected behaviour or a bug?

[n0v1]

Fixed as of mariadb version 3.5.0-rc.0 (not published yet).