On Tuesday, October 31, 2023 6:45 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > b) Currently I have restricted 'alter subscription.. refresh > > publication with copy=true' when failover=true (on a similar line of > > two-phase). The reason being, refresh with copy=true will go for > > table-sync again and since failover was set in main-slot after > > table-sync was done, it will need going through the same transition of > > 'p' to 'e' for main slot making it unsyncable for that time. Should it > > be allowed? > > > > Yeah, I also think we can't allow refresh with copy=true when 'failover' is > enabled. > > I think the current implementation of this flag seems a bit clumsy because > 'failover' is a slot property and we are trying to map it to plugin_options. > It has > to be considered similar to the opt_temporary option while creating the slot. > > We have create_replication_slot and drop_replication_slot in repl_gram.y. How > about if introduce alter_replication_slot and handle the 'failover' flag with > that? > The idea is we will either enable 'failover' at the time > create_replication_slot by > providing an optional failover option or execute a separate command > alter_replication_slot. I think we probably need to perform this command > before the start of streaming. > > I think we will have the following options to allow alter of the 'failover' > property: (a) we can allow altering 'failover' only for the 'disabled' > subscription; > to achieve that, we need to open a connection during alter subscription and > change this property of slot; (b) apply worker detects the change in > 'failover' > option; run the alter_replication_slot command; this needs more analysis as > apply_worker is already doing streaming and changing slot property in > between could be tricky.
I think for approach b), one challenge is the handling of the error case. E.g. If the apply worker errored out when executing the alter_replication_slot command, it may not be able to retry that after restarting, because it won't know if the value has changed before. (Or we have to execute alter_replication_slot always at the beginning in apply worker which seems not great). Best Regards, Hou zj
