From: pgsql-hackers-ow...@postgresql.org > [mailto:pgsql-hackers-ow...@postgresql.org] On Behalf Of Craig Ringer > On 13 April 2017 at 14:59, Tsunakawa, Takayuki > <tsunakawa.ta...@jp.fujitsu.com> wrote: > > > 2. Make transaction_read_only GUC_REPORT This is to avoid the added > > round-trip by SHOW command. It also benefits client apps that want to > know when the server gets promoted? And this may simplify the libpq code. > > I don't understand yet why we need to provide this feature for older servers > by using SHOW. Those who are already using <= 9.6 in production completed > the system or application, and their business is running. Why would they > want to just replace libpq and use this feature? > > I think "transaction_read_only" is a bit confusing for something we're > expecting to change under us. > > To me, a "read only" xact is one created with > > BEGIN READ ONLY TRANSACTION; > > .... which I would not expect to become read/write under me, since I > explicitly asked for read-only. > > It's more like "session read only" that we're interested in IMO.
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. Regards Takayuki Tsunakawa
libpq-fast-connect-read-only.patch
Description: libpq-fast-connect-read-only.patch
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