Situation:
Parallel execution step running some script on several nodes in parallel, parameterized with workers equal to e.g. 2.

Expected:
I'd expect to see a maximum of <workers> (e.g. 2) steps running simultaneously and another one started as soon as one of them is done.

Actual:
It seems to work fine for the first group, i.e. for workers set to 2 just two steps are started initially and as soon as those are done another two are started; but when they start running everything else seems to be triggered at once (meaning as fast as qb/the node can handle it - until the node runs out of memory in this case).

Log excerpt showing just the "checking step execute condition" (order according to qb log):
12:21:35,205 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:21:35,324 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:21:48,531 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:21:50,893 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:05,501 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:05,620 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:05,741 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:05,868 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:05,987 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,107 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,231 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,350 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,469 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,588 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,716 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,834 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:06,952 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,067 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,176 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,303 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,421 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,555 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,676 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,794 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:07,915 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,037 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,156 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,274 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,407 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,526 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,644 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,773 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:08,883 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,001 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,119 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,255 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,373 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,494 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,621 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,739 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,857 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:09,995 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,117 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,235 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,352 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,479 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,618 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,738 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,857 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:10,987 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,104 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,224 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,363 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,481 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,598 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,731 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,853 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:11,971 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:12,103 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:12,223 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:12,357 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:12,475 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:13,069 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:13,623 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:13,743 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:13,866 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:13,990 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,107 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,232 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,352 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,474 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,591 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,717 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,835 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:14,958 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,079 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,206 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,324 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,448 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,568 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,691 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,809 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:15,934 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,055 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,181 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,300 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,432 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,549 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,678 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,797 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:16,926 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,043 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,171 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,303 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,433 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,555 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,676 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,806 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:17,926 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,061 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,179 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,311 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,429 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,571 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,692 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,828 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:18,946 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,077 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,196 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,330 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,470 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,589 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,721 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,839 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:19,969 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,086 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,222 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,340 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,472 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,590 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,722 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,844 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:20,962 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,097 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,219 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,352 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,475 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,608 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,725 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,859 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:21,976 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,113 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,232 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,369 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,491 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,609 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,742 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,860 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:22,994 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,113 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,252 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,375 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,508 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,626 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,744 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,872 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:23,990 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,124 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,248 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,385 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,503 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,637 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,755 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:24,903 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,021 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,165 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,283 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,400 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,534 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,652 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,790 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:25,908 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,049 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,167 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,285 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,419 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,537 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,671 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,791 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:26,933 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,050 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,168 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,303 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,421 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,555 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,675 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,810 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:27,928 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,046 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,178 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,296 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,429 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,546 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,671 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,806 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:28,929 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:29,064 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:29,188 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:29,323 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:29,442 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:29,560 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...
12:22:29,698 [master>execute>parallel>clean-up?selectedNode=<somenode>] INFO - Checking step execute condition...