Hello This is a well documented feature of Hot-Standby Replication.
see: http://www.postgresql.org/docs/9.2/static/runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-STANDBY Regards, -- Valentin ვალენტინ გოგიჩაშვილი Valentine Gogichashvili On Wed, Aug 28, 2013 at 2:30 AM, <pc...@contigo.com> wrote: > The following bug has been logged on the website: > > Bug reference: 8404 > Logged by: Pius Chan > Email address: pc...@contigo.com > PostgreSQL version: 9.1.9 > Operating system: Linux version 2.6.32-279.14.1.el6.x86_64 > Description: > > When investigating an "out of memory" issue in hot standby, it is found > that > JDBC can block the application of replicated transaction log to hot > standby. > The set up of the test is as follows: > > > Set up: > ======= > Set up a master db cluster and hot standby db cluster using async streaming > replication. On master database server, create a database TEST. Implement a > cron job which on every minute: > - drop table if exists heartbeat; > - create table heartbeat (timenow timestamp); > - insert into heartbeat values (now()); > - this is to ensure transaction entry is generated at least every minute. > > > Test 1 - psql does not block replication > ======================================== > - on hot standy db server, start a psql session (session 1), then submit > the > following: > psql> begin; > psql> select now(); > ..... idle > > > - start another psql session on hot standby db server and run the following > SQLs to monitor the replication delay: > > > select current_timestamp, pg_last_xact_replay_timestamp(), > current_timestamp-pg_last_xact_replay_timestamp() as replication_delay, > pg_last_xlog_receive_location(); > > > Result: it is found that session 1 does > not block replication. > > > > > Test 2 - JDBC can block replication > ==================================== > - write a Java test program to connect to hot standby TEST database > - in the test program, submit the following SQLs: > > begin; > select now(); > then sleep for 2 minutes > > > - on hot standby db server, start another psql session and monitor the > replication delay with the same SQL. > > > Results: it is found that during the 2 minutes sleeping time, > pg_last_xlog_receive_location is advancing but > pg_last_xact_replay_timestamp > is stuck. The result of "select * from heartbeat" does not change. > > > Is that a bug in JDBC driver? > > > > -- > Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-bugs >
