Once we have checked the archives and our system views, we are ready to check for system processes. Checking for system processes might look a little crude, but it has been proven to be highly effective.

On the master, we can simply check for a process called wal_sender. On the slave, we have to check for a process called wal_receiver.

Let's check out what we are supposed to see on the master first. The following command does the job:

ps ax | grep "wal sender"

Here is the output:

9314   ??  Ss     0:00.00 postgres: wal sender process
hs ::1(61498) idle

On Linux, we can see that the process carries not only its purpose (in this case, wal_sender) but also the name of the end user and network-related information. In our case, we can see that somebody has connected from localhost through port 61498.

The situation on the slave is pretty simple as well:

9313   ??  Ss     0:00.00 postgres: wal receiver process

All we see is a process informing us that we are consuming...