Hi Tatsuo, Thank you for the explanation.
Best regards, On Sun, 2009-12-20 at 18:25 +0900, Tatsuo Ishii wrote: > > Hi, > > > > I've a pgpool-II replication + load balance environment with seven > > backend servers running PostgreSQL 8 and CentOS 5. > > > > The backend 0 (master node) runs both pgpool-II and PostgreSQL. I'm > > setting up online recovery with rsync using the same script for both 1st > > and 2nd stage commands. > > > > Considering a scenario where the backend 0 (which runs pgpool-II and > > PostgreSQL) PostgreSQL is disconnected from pgpool-II, I have the > > following questions: > > > > * How online recovery is supposed to work in this case? > > 1) backend 1 is chosen as the new master node. > > 2) pgpool-II connects to PostgreSQL on backend 1. This connection is > different from ordinary backend connection. > > 3) pgpool-II requests backend 1 to execute CHECKPOINT. > > 4) pgpool-II requests backend 1 to execute "SELECT pgpool_recovery" > which will execute online recovery stage 1 command. > > 5) pgppool-II waits until all client connection disconnected. > > 6) pgpool-II requests backend 1 to execute CHECKPOINT. > > 7) pgpool-II requests backend 1 to execute "SELECT pgpool_recovery" > which will execute online recovery stage 2 command. > > 8) pgpool-II requests backend 1 to execute "SELECT pgpool_remote_start" > which will execute "pgpool_remote_start" script, which is supposed > to remote start postmaster on backend 0. > > 9) backend 0 connected again and recovery done. > > > * Do I need to have pgpool-II installed on all backend servers? If so, I > > will have dummy pgpool-II processes running on backend serves just to > > have the pgpool communication manager running and be able to run > > pcp_recovery_node from another backend? > > No. What you need on all backend servers are: > > 1) C functions under pgpool-II/sql/pgpool-recovery installed > (pgpool_recovery and pgpool_remote_start). > > 2) pgpool_remote_start script installed under PostgreSQL database > cluster directory (/usr/local/pgsql/data). > > 3) recovery scripts installed under PostgreSQL database cluster > directory (/usr/local/pgsql/data). > > > * How 2nd stage of online recovery is supporsed to work if I am > > recovering from a different backend than the one running pgpool-II and > > PostgreSQL will continue accepting connections? Is cascading pgpool-II > > connections to the backend servers a correct solution or workaround > > here? > > See above. > -- > Tatsuo Ishii > SRA OSS, Inc. Japan
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