Lets see pgsql deal with 15000 client connections.
One of the Planetscale guys did a podcast and said at GitHub every MySQL instance is doing like 50k+ connections while if you need more than 100 connections in Postgres you already need PgBouncer.
It's just an architectural decision to spawn a process per connection that Postgres made long time ago.
It's a tradeoff like most decisions.
Back in the days MySQL had huge issues with scaling to multi-core systems (maybe they fixed it now, I haven't used MySQL for a long time) while Postgres never had this problem.
When designing an application around Postgres you just have to take into account that:
1. opening a new connection is rather expensive, so you should have a connection pool
2. opening too many connections is problematic, so you should keep the size of your pool rather small and return connections back into the pool ASAP
That's it.
It's not that hard in practice.
Postgres uses an old design model which predates threads; I have no idea if they have made any progress in updating their design. In the past I have heard the core devs talk about how difficult it would be to do this.
Oracle Database moved to a hybrid process/thread model at some point, this is the superior solution ( I have no idea if it was done well or not, but from standpoint of how to achieve better leverage of CPU vs IO, this is the way ).
If the PG devs had enough time/money, I am sure they would move towards a hybrid model where the focus would be on processor affinity with IO being all tied to events.
Unrelated to mysql - I do consider using redis in any capacity a blunder (it's likely ok for nodejs users, I suppose)
[0]: http://dimitrik.free.fr/MySQL_Connect_2013/MySQL_Perf-Connec...
You can have as much connections as you want, but you'll have to trade it for having lower work mem numbers, which hurts performance. Traditional advice is to keep it below 500 per PostgreSQL instance (I'd say physical host).
I've ran dozens of micro services handling thousands of requests per second with a total connection limit of around 200 of which most was still unused - all without any server-side pooler.
> it doesn't matter if they are all active
It does, if the connection is inactive (doesn't hold an open transaction) you should close it or return it to the pool.
Between transactions? Yes, absolutely
In fact, many libraries do it automatically.
For example, SQLAlchemy doc explicitly says [0]:
> After the commit, the Connection object associated with that transaction is closed, causing its underlying DBAPI connection to be released back to the connection pool associated with the Engine to which the Session is bound.
I expect other reasonably sane libs for working with transactional databases do the same.
So, if you are doing pooling correctly, you can only run out of available connections if you want to have a lot of long running transactions.
So, why would you want every of your 50k frontends keep an open transaction simultaneously?
[0] https://docs.sqlalchemy.org/en/20/orm/session_basics.html#co...
Of course, the better design is to write a nonblocking worker that can run async requests on a single connection, and not need a giant pool of blocking workers, but that is a major architecture plan that can't be added late in a project that started as blocking worker pools. MySQL has always fit well with those large blocking worker pools. Postgres less so.
From the perspective of keeping the number of open connections low it doesn't really matter if you close it or return to the pool, because in either case the connection becomes available to other clients.
If you are saying that a connection pool can be shared between processes without pgbouncer, that is news to me.
> Parent comment is talking about one connection per process with 50k processes.
It is actually not clear what parent comment was talking about. I don't know what exactly did they mean by "front ends".