On Thu, 17 Jan 2019 at 19:38, Tatsuo Ishii <is...@sraoss.co.jp> wrote:
> >> >> >> > From: Tatsuo Ishii [mailto:is...@sraoss.co.jp] > >> >> >> >> But pg_is_in_recovery() returns true even for a promoting > >> standby. So > >> >> >> >> you have to wait and retry to send pg_is_in_recovery() until it > >> >> >> >> finishes the promotion to find out it is now a primary. I am > not > >> sure > >> >> >> >> if backend out to be responsible for this process. If not, > libpq > >> >> would > >> >> >> >> need to handle it but I doubt it would be possible. > >> >> >> > > >> >> >> > Yes, the application needs to retry connection attempts until > >> success. > >> >> >> That's not different from PgJDBC and other DBMSs. > >> >> >> > >> >> >> I don't know what PgJDBC is doing, however I think libpq needs to > do > >> >> >> more than just retrying. > >> >> >> > >> >> >> 1) Try to find a node on which pg_is_in_recovery() returns false. > If > >> >> >> found, then we assume that is the primary. We also assume that > >> >> >> other nodes are standbys. done. > >> >> >> > >> >> >> 2) If there's no node on which pg_is_in_recovery() returns false, > >> then > >> >> >> we need to retry until we find it. To not retry forever, there > >> >> >> should be a timeout counter parameter. > >> >> >> > >> >> >> > >> >> > IIRC this is essentially what pgJDBC does. > >> >> > >> >> Thanks for clarifying that. Pgpool-II also does that too. Seems like > a > >> >> common technique to find out a primary node. > >> >> > >> >> > >> > Checking the code I see we actually use show transaction_read_only. > >> > > >> > Sorry for the confusion > >> > >> So if all PostgreSQL servers returns transaction_read_only = on, how > >> does pgJDBC find the primary node? > >> > >> well preferSecondary would return a connection. > > This is not my message :-) > > > I'm curious; under what circumstances would the above occur? > > Former primary goes down and one of standbys is promoting but it is > not promoted to new primary yet. > seems like JDBC might have some work to do...Thanks I'm going to wait to implement until we resolve this discussion Dave > >
