Re: A question regarding streaming replication

Hey all,

I have a  questions regarding streaming replication that I would like to ask in order to understand the feature better : 

I have 2 nodes configured with replication (primary + secondary).

In my primary I configured streaming replcation + archiving. My archive command : 

gzip < %p > /var/lib/pgsql/archive/%f ; echo "archiving wal %f"

Correct me if I'm wrong but my archive_command will be run when the archive_timeout is reached or when the wal is full (16MB). The wal file is created with default size of 16MB and it will be archived only after 16MB of wal records will be created.

In my secondary I have the following settings : 

restore_command = 'rsync -avzhe ssh postgres@my_primary :/var/lib/pgsql/archive/%f /var/lib/pgsql/archive/%f ; gunzip < /var/lib/pgsql/archive/%f > %p; echo "restore command was launched"'

archive_cleanup_command = '/usr/pgsql-9.6/bin/pg_archivecleanup /var/lib/pgsql/archive %r; "archive_cleanupup for %r was launched"'

Which means, that the restore command on the secondary connects to the primary, copies the wal file from the archive dir , unzip it and saves it in the pg_xlog dir of the database.

my question : 

When exactly the restore_command will be used ? I use streaming replication therefore wal records are passed through wal_sender and wal receiver. I dont see in my logs in the secondary that the restore_command is used but I see that the same wal files as in the primary are exists on the pg_xlog in the secondary. Does the streaming replication generates wals on the secondary from the wals records that it receives from the primary ?