From: Haribabu Kommi [mailto:kommi.harib...@gmail.com] > target_session_attrs checks for the default_transaction_readonly or not?
PG 11 uses transaction_read_only, not default_transaction_readonly. That's fine, because its purpose is to get a read-only session as the name suggests, not to connect to a standby. > target_server_type checks for whether the server is in recovery or not? Yes. > I feel having two options make this feature complex to use it from the user > point of view? > > The need of two options came because of a possibility of a master server > with default_transaction_readonly set to true. Even if the default > transaction > is readonly, it is user changeable parameter, so there shouldn't be any > problem. No. It's not good if the user has to be bothered by default_transaction_read_only when he simply wants to a standby. > how about just adding one parameter that takes the options similar like > JDBC? > target_server_type - Master, standby and prefer-standby. (The option names > can revised based on the common words on the postgresql docs?) "Getting a read-only session" is not equal to "connecting to a standby", so two different parameters make sense. > And one more thing, what happens when the server promotes to master but > the connection requested is standby? I feel we can maintain the existing > connections > and later new connections can be redirected? comments? Ideally, it should be possible for the user to choose the behavior like Oracle below. But that's a separate feature. 9.2 Role Transitions Involving Physical Standby Databases https://docs.oracle.com/en/database/oracle/oracle-database/18/sbydb/managing-oracle-data-guard-role-transitions.html#GUID-857F6F45-DC1C-4345-BD39-F3BE7D79F1CD -------------------------------------------------- Keeping Physical Standby Sessions Connected During Role Transition As of Oracle Database 12c Release 2 (12.2.0.1), when a physical standby database is converted into a primary you have the option to keep any sessions connected to the physical standby connected, without disruption, during the switchover/failover. To enable this feature, set the STANDBY_DB_PRESERVE_STATES initialization parameter in your init.ora file before the standby instance is started. This parameter applies to physical standby databases only. The allowed values are: NONE — No sessions on the standby are retained during a switchover/failover. This is the default value. ALL — User sessions are retained during switchover/failover. SESSION — User sessions are retained during switchover/failover. -------------------------------------------------- Would you like to work on this patch? I'm not sure if I can take time, but I'm willing to do it if you don't have enough time. As Tom mentioned, we need to integrate and clean patches in three mail threads: * Make a new GUC_REPORT parameter, server_type, to show the server role (primary or standby). * Add target_server_type libpq connection parameter, whose values are either primary, standby, or prefer_standby. * Failover timeout, load balancing, etc. that someone proposed in the other thread? (I wonder which of server_type or server_role feels natural in English.) Or, would you like to share the work, e.g., libpq and server-side? Regards Takayuki Tsunakawa
