PostgreSQL Exception: “An I/O error occured while sending to the backend” - postgresql

Question

I run two web app in a machine and one DB in another machine.(They use the same DB)
One can run very well,But another one always down after about 4 hours.
Here is error information:
Error 2014-11-03 13:31:05,902 [http-bio-8080-exec-7] ERROR spi.SqlExceptionHelper - An I/O error occured while sending to the backend.
| Error 2014-11-03 13:31:05,904 [http-bio-8080-exec-7] ERROR spi.SqlExceptionHelper - This connection has been closed.
Postgresql logs:
2014-10-26 23:41:31 CDT WARNING: pgstat wait timeout
2014-10-27 01:13:48 CDT WARNING: pgstat wait timeout
2014-10-27 03:55:46 CDT LOG: could not receive data from client: Connection timed out
2014-10-27 03:55:46 CDT LOG: unexpected EOF on client connection
Who caused this problem, app or database? or net?

Answer 1

Reason:
At this point it was clear that the TCP connection that was sitting idle was already broken, but our app still assumed it to be open. By idle connections, I mean connections in the pool that aren’t in active use at the moment by the application.
After some search, I came to the conclusion that the network firewall between my app and the database is dropping the idle/stale connections after 1 hour. It seemed to be a common problem that many people have faced.
Solution:
In grails, you can set this in DataSource.groovy.
environments {
development {
dataSource {
//configure DBCP
properties {
maxActive = 50
maxIdle = 25
minIdle = 1
initialSize = 1
minEvictableIdleTimeMillis = 60000
timeBetweenEvictionRunsMillis = 60000
numTestsPerEvictionRun = 3
maxWait = 10000
testOnBorrow = true
testWhileIdle = true
testOnReturn = false
validationQuery = "SELECT 1"
}
}
}
}