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Why would you do 50k+ connections if they can't be active all at once either way? Unless you have 50k+ cores and IO beefy enough not to get overwhelmed due to t

Why would you do 50k+ connections if they can't be active all at once either way? Unless you have 50k+ cores and IO beefy enough not to get overwhelmed due to that. 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.

samlambert 2y ago
because people run large amounts of front ends and workers that create a significant amount of connections. it doesn't matter if they are all active.
- throwaway313373 2y ago
  Why would you want every "frontend" keep an open connection all the time? > 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.
  - samlambert 2y ago
    so you are suggesting you close a connection between queries?
    - throwaway313373 2y ago
      Between queries in the same transaction? No 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#committing https://docs.sqlalchemy.org/en/20/orm/session_basics.html#co...
      - nrdvana 2y ago
        Because there's an overhead to make a connection, authenticate, set the default parameters on the connection, etc. I've never seen a framework that closed db connections between requests. 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.
        throwaway313373 2y ago
        As I said, you can return the connection to the connection pool. 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.
        deleted 2y ago
        [deleted]
        nrdvana 2y ago
        I might not be understanding what you're pointing out here. It sounds to me like sqlalchemy is talking about a pool of connections within one process, in which case releasing back to that pool does not close the connection by that process to the database. Parent comment is talking about one connection per process with 50k processes. My comment was that you don't need that many processes if each process can handle hundreds of web requests asynchronously. If you are saying that a connection pool can be shared between processes without pgbouncer, that is news to me.
        throwaway313373 2y ago
        Of course, you're right, it is not possible to to share a connection pool between processes without pgbouncer. > 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".

samlambert 2y ago

because people run large amounts of front ends and workers that create a significant amount of connections. it doesn't matter if they are all active.

throwaway313373 2y ago
Why would you want every "frontend" keep an open connection all the time? > 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.
- samlambert 2y ago
  so you are suggesting you close a connection between queries?
  - throwaway313373 2y ago
    Between queries in the same transaction? No 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#committing https://docs.sqlalchemy.org/en/20/orm/session_basics.html#co...
    - nrdvana 2y ago
      Because there's an overhead to make a connection, authenticate, set the default parameters on the connection, etc. I've never seen a framework that closed db connections between requests. 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.
      - throwaway313373 2y ago
        As I said, you can return the connection to the connection pool. 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.
        deleted 2y ago
        [deleted]
        nrdvana 2y ago
        I might not be understanding what you're pointing out here. It sounds to me like sqlalchemy is talking about a pool of connections within one process, in which case releasing back to that pool does not close the connection by that process to the database. Parent comment is talking about one connection per process with 50k processes. My comment was that you don't need that many processes if each process can handle hundreds of web requests asynchronously. If you are saying that a connection pool can be shared between processes without pgbouncer, that is news to me.
        throwaway313373 2y ago
        Of course, you're right, it is not possible to to share a connection pool between processes without pgbouncer. > 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".