Turning slaves into masters

A slave can be a wonderful thing if you want to scale up reads or get a backup of your data. But a slave might not always have to remain a slave. At some point, you might need to turn a slave into a master. In classic cases, this happens when the original master crashes or the hardware has to be changed.

Tip

Be careful when promoting a slave. It cannot easily be demoted anymore. Once a slave has turned into a master, it can be a slave again only after performing a complete resync or after running pg_rewind, which will be available by default in PostgreSQL 9.5.

PostgreSQL offers some simple ways to do this. The first way, and most likely the most convenient way, to turn a slave into a master is by using pg_ctl:

iMac:slavehs$ pg_ctl -D /target_directory promote
server promoting
iMac:slavehs$ psql test
psql (9.2.4)
Type "help" for help.
test=# CREATE TABLE sample (id int4);
CREATE TABLE

The promote command will signal the postmaster and turn your slave into a master...