On 12/09/2011 01:02 AM, Tomas Vondra wrote:
On 8 Prosinec 2011, 17:11, Marc Cousin wrote:
Le Thu, 8 Dec 2011 09:29:28 -0600,
- admission control, queuing and resource limiting to optimally
load a machine. Some limited level is possible with external
pooling, but only by limiting concurrent workers.
Oracle has natively two ways of handling inbound connections:
- Dedicated, which is very similar to the PostgreSQL way of
accepting connections: accept(), fork() and so on
- Shared, which is based on processes listening and handling the
connections (called dispatchers) and processes doing the real work
(called workers, obviously). All of this works internally with
some sort of queuing and storing results in shared memory (I don't
remember the details of it)
The advantage of this second architecture being of course that you
can't have more than N workers hitting your database
simultaneously. So it's easier to keep the load on the server to a
reasonable value.
you have a couple of very good options to achieve the same in postgres
-- pgbouncer, pgpool.
I wish it was the same (I use and like both pgbouncer and pgpool too,
and they do a good job, I'm not arguing on that). But unfortunately it
isn't: you still have the notion of session for each connected client
in Oracle when using the shared servers model.
True, it is not exactly the same, it's similar. I don't think PostgreSQL
will ever provide 'shared backends' the way Oracle does - it would require
significant code change. Most of the benefits can be achieved by using a
connection pool without the added complexity.
Yep - a connection pool that could save and restore session state,
separating "executor/backend" from "connection/session", would produce
much the same result with a lot less complexity. It's one of the reasons
I'd love to see in-core pooling, because I don't see how an out-of-core
solution can maintain session state like advisory locks, HOLD cursors, etc.
--
Craig Ringer
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