pg_basebackup and multiple tablespaces

Question

I have the following case:

• the master database has an additional tablespace
• I'm trying to replicate the master with the pg_basebackup tool
• the directory / partition layout on the slave is the same as on the master

What parameters should I use to set up replication safely? Do I need to map tablespace with -T parameter or is it only required if I am doing pg_basebackup on the master? pg_basebackup is generaly safe? Data not be deleted from the master?

My command is:

db_slave# pg_basebackup -h db_master -p 5433 -U replication -D /var/lib/postgresql/12/main -P -Xs -Fp -R

But I get:

pg_basebackup: error: directory "/home/db" exists but is not empty
pg_basebackup: removing data directory "/var/lib/postgresql/12/main"

Tablespace is store in /home/db. Thanks a lot for all answers.

Answer 1

If you use pg_basebackup without -T, it assumes that the tablespace directories are in the same location as on the primary database machine. The documentation states:

As with the main target directory, newdir need not exist already, but if it does exist it must be empty.

If you want to backup the tablespaces to a different location, use the -T option.