Feedback-ID: id4a34324:Fastmail
Date: Thu, 9 May 2024 12:14:55 -0700
From: Andres Freund <andres@anarazel.de>
To: Dave Cramer <davecramer@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: request for database identifier in the startup packet
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Hi,

On 2024-05-09 14:20:49 -0400, Dave Cramer wrote:
> On Thu, 9 May 2024 at 12:22, Robert Haas <robertmhaas@gmail.com> wrote:
> > On Thu, May 9, 2024 at 8:06 AM Dave Cramer <davecramer@gmail.com> wrote:
> > > The JDBC driver is currently keeping a per connection cache of types in
> > the driver. We are seeing cases where the number of columns is quite high.
> > In one case Prevent fetchFieldMetaData() from being run when unnecessary. ·
> > Issue #3241 · pgjdbc/pgjdbc (github.com) 2.6 Million columns.
> > >
> > > If we knew that we were connecting to the same database we could use a
> > single cache across connections.
> > >
> > > I think we would require a server/database identifier in the startup
> > message.
> >
> > I understand the desire to share the cache, but not why that would
> > require any kind of change to the wire protocol.
> >
> > The server identity is actually useful for many things such as knowing
> which instance of a cluster you are connected to.
> For the cache however we can't use the IP address to determine which server
> we are connected to as we could be connected to a pooler.
> Knowing exactly which server/database makes it relatively easy to have a
> common cache across connections. Getting that in the startup message seems
> like a good place

ISTM that you could just as well query the information you'd like after
connecting. And that's going to be a lot more flexible than having to have
precisely the right information in the startup message, and most clients not
needing it.

Greetings,

Andres Freund