Re: get/setReadOnly broken if default_transaction_read_only on

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>
Cc: "Johann 'Myrkraverk' Oskarsson" <johann(at)2ndquadrant(dot)com>, PostgreSQL JDBC <pgsql-jdbc(at)postgresql(dot)org>
Subject: Re: get/setReadOnly broken if default_transaction_read_only on
Date: 2012-06-08 13:47:19
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Craig Ringer <ringerc(at)ringerc(dot)id(dot)au> writes:
> On 06/08/2012 04:19 PM, Johann 'Myrkraverk' Oskarsson wrote:
>> Craig Ringer<ringerc(at)ringerc(dot)id(dot)au> writes:
>>> The JDBC driver really needs a way to grab everything it needs to know
>>> efficiently during initial connection setup, with some extensibility
>>> so connection parameters can specify other things to request and cache
>>> when the connection is first established.

> I was thinking more of running something like:
> ... preferably combined with a mechanism for the server to notify (or
> NOTIFY) the JDBC client when a pg_ctl reload or a SET causes settings to
> change.

Running pg_settings() seems like a dead end to me, precisely because you
won't know about any subsequent changes; and most of the parameters that
JDBC might care about are changeable. LISTEN/NOTIFY is not the answer
either, for the reasons you mention as well as some others.

There already is a mechanism to notify clients of changes in selected
GUC settings, but currently the set of parameters so reported is
hard-wired. Possibly pgsql-hackers would consider a proposal to let
the GUC_REPORT flag get set on client-selected parameters.

regards, tom lane

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