pg-pool v2.0.10 inspects the client _querable attribute. This attribute was not added until pg v7.5.0. Unfortunately pg versions prior to 7.5.0 do not block 2.0.10. The impact of this is that pg-pool v2.0.10 releasing a client connection with that attribute missing causes the client to be removed rather than released. The performance impact on removing postgres client connections instead of keeping them in the pool is extremely significant. For example postgres CPU utilization increased 6x over a 30 minute workload simulation resulting in 10x increase in execution times of most postgres query/commands.

I understand that this is present only in older versions and is fixed by newer versions of pg but it should be documented or blocked if possible as the possible symptoms -- extremely high postgres CPU utilization can take considerable time to narrow down (multiple weeks in my case).