Tsunakawa, Takayuki wrote: > From: Laurenz Albe [mailto:laurenz.a...@cybertec.at] > > I think that transaction_read_only is good. > > > > If it is set to false, we are sure to be on a replication primary or > > stand-alone server, which is enough to know for the load balancing use case. > > As Tatsuo-san said, setting default_transaction_read_only leads to a > misjudgement of the primary.
Yes, you can have a false negative, i.e. fail to recognize a primary server. > > I deem it unlikely that someone will set default_transaction_read_only to > > FALSE and then complain that the feature is not working as expected, but > > again > > I cannot prove that claim. > > I wonder what default_transaction_read_only exists for. For maing the > database by default > and allowing only specific users to write to the database with "CREATE/ALTER > USER SET > default_transaction_read_only = false"? I'd guess that the main use of default_transaction_read_only is to make sure an application (that isn't smart enough to change the parameter) won't modify any data. > I'm sorry to repeat myself, but anyway, I think we need a method to connect > to a standby > as the original desire, because the primary instance may be read only by > default while > only limited users update data. That's for reducing the burdon on the > primary and > minimizing the impact on users who update data. For example, > > * run data reporting on the standby > * backup the database from the standby > * cascade replication from the standby I see. But then the new value should not be called "prefer-read", because that would be misleading. It would also not be related to the existing "read-write". For what you have in mind, there should be the options "primary-required" and "standby-preferred", however we implement them. Have there been a lot of complaints that the existing "read-write" is not good enough to detect replication primaries? > > As Robert said, transaction_read_only might even give you the option to > > use the feature for more than just load balancing between replication master > > and standby. > > What use case do you think of? If you want to load balance the workload > between > the primary and standbys, we can follow PgJDBC -- targetServerType=any. One use case I can think of is logical replication (or other replication methods like Slony). You can use the feature by setting default_transaction_read_only = on on the standby. Yours, Laurenz Albe