Open Stack

On 08/01/2018 11:32 AM, melanie witt wrote:

> I think it's definitely a significant issue that troubleshooting "No allocation
> candidates returned" from placement is so difficult. However, it's not
> straightforward to log detail in placement when the request for allocation
> candidates is essentially "SELECT * FROM nodes WHERE cpu usage < needed and disk
> usage < needed and memory usage < needed" and the result is returned from the API.

I think the only way to get useful info on a failure would be to break down the 
huge SQL statement into subclauses and store the results of the intermediate 
queries.  So then if it failed placement could log something like:

hosts with enough CPU: <list1>
hosts that also have enough disk: <list2>
hosts that also have enough memory: <list3>
hosts that also meet extra spec host aggregate keys: <list 4>
hosts that also meet image properties host aggregate keys: <list 5>
hosts that also have requested PCI devices: <list 6>

And maybe we could optimize the above by only emitting logs where the list has a 
length less than X (to avoid flooding the logs with hostnames in large clusters).

This would let you zero in on the things that finally caused the list to be 
whittled down to nothing.

Chris