721f7bd3cb
Commit 274bb2b3857cc987cfa21d14775cae9b0dababa5 made it possible to specify multiple IPs in a connection string, but that's not good enough for the case where you have a read-write master and a bunch of read-only standbys and want to connect to whichever server is the master at the current time. This commit allows that, by making it possible to specify target_session_attrs=read-write as a connection parameter. There was extensive discussion of the best name for the connection parameter and its values as well as the best way to distinguish master and standbys. For now, adopt the same solution as JDBC: if the user wants a read-write connection, issue 'show transaction_read_only' and rejection the connection if the result is 'on'. In the future, we could add additional values of this new target_session_attrs parameter that issue different queries; or we might have some way of distinguishing the server type without resorting to an SQL query; but right now, we have this, and that's (hopefully) a good start. Victor Wagner and Mithun Cy. Design review by Álvaro Herrera, Catalin Iacob, Takayuki Tsunakawa, and Craig Ringer; code review by me. I changed Mithun's patch to skip all remaining IPs for a host if we reject a connection based on this new parameter, rewrote the documentation, and did some other cosmetic cleanup. Discussion: http://postgr.es/m/CAD__OuhqPRGpcsfwPHz_PDqAGkoqS1UvnUnOnAB-LBWBW=wu4A@mail.gmail.com
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.