Redash queries stuck in queue

[aakashb-kayzen]

Redash Version : Version: 7.0.0+b17535 (15c815f)
OS : Ubuntu 18.04.2 LTS

Issue : We frequently see queries getting stuck for long (several minutes) in queue, inspite of the server hosting redash not being busy.
On checking the server, we see that most of the celery processes are idle doing nothing (in htop CPU is 0% and TIME+ is unchanging), while a few celery processes have 100% CPU and have become orphan (PPID=1). [See screenshot below]

Restarting redash fixes the issue.

Question :

• Is this an expected issue with celery (as described in previous threads here and here) ?
• Will upgrading to newer versions that use RQ help fix this issue ?