But no one says you need a separate connection pool for each client application. There are cases when it's the right thing, but you can just as well have a sing

But no one says you need a separate connection pool for each client application. There are cases when it's the right thing, but you can just as well have a single connection pool for each PostgreSQL instance (and all apps will go through that). So you absolutely don't need "8 instances" at peak or whatever. The problem with Postgres vs. many connections is a simple combination of two simple facts. Firstly, Postgres has a dedicated process managing each connection - which significantly simplifies some of the programming because most resources are "private" etc. This made perfect sense back when machines very few cores, threading was much more expensive, etc. And development time is always precious, of course. Secondly, people often don't distinguish between active and idle connections. But a system with X cores reaches top throughput at 2X-3X active connections, and at some point the throughput tanks because the active backends have to share resources (CPU, work_mem, etc.). And the database and/or DBA has to manage that somehow - if you have 128GB of RAM available for query processing, it matters if you allow 100 or 10000 connections. With 100x more connections you can't allow the backends to use as much memory, which probably means less efficient sorts etc. You may assume most connections will be idle at any given time, but that may easily change (a bug in new app version or whatever), storming the DB, exhausting resources, etc. Moreover, some (fairly hot) parts of the transaction management code need to walk active connections to check visibility etc, and the more connections you have the more expensive this is. And there are probably more places with similar behavior. We've fixed / optimized lot of them, because the number of cores is growing and it was hurting even "reasonably" configured instances, but that gets you maybe to 500 - 1000 connections (?), not 100k. And I don't think that'll change anytime soon, so your best bet is still a connection pool. Now, I'm not claiming it's ideal - but there simply are historical and practical reasons why things are designed the way they are, and it's not a matter of swooping in and optimizing one or two places.