Re: [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.

On Wed, May 24, 2017 at 3:16 AM, Tsunakawa, Takayuki
<tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:
> I confirmed that the attached patch successfully provides:
>
> * target_session_attrs=read-only
> * If the server is >= 10, avoid the round-trip for SHOW transaction_read_only.
>
> For this, I added a GUC_REPORT variable session_read_only which indicates the session's default read-only status. The characteristics are:
>
> * It cannot be changed directly by the user (postgresql.conf, SET, etc.)
> * Its value is the same as default_transaction_read_only when not in recovery.
> * Its value is false during recovery.
>
> Could you include this in PG 10? I think these are necessary as the bottom line to meet the average expectation of users (please don't ask me what's the average; the main reasons are that PostgreSQL provides hot standby, PgJDBC enables connection to the standby (targetServerType=slave), and PostgreSQL emphasizes performance.) Ideally, I wanted to add other features of PgJDBC (e.g. targetServerType=preferSlave), but I thought this is the limit not to endanger the quality of the final release.

I've already stated my position on this, which is that:

* target_session_attrs=read-only is a perfectly good new feature, but
we're past feature freeze, so it's material for v11.

* I'm not opposed to adding a GUC_REPORT GUC of some kind, but I see
no urgency about that either. The feature works fine as it is. The
fact that it could possibly be made to work more efficiently is not a
critical bug.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company