Chapter 4 part 1 - Initialising the data directory

Initialising the data directory

A PostgreSQL instance is composed by a shared memory process and a data area managed by the postgres processes. The data area is initialised by initdb which requires an empty and writable directory to succeed. The binary location depends on the installation method, take a look to the chapters 3 and 2 for further informations. Initdb accepts various parameters. If not supplied then the probam will try to get the informations from the environment variables.

Its basic usage is
initdb DATADIRECTORY
If the variable PGDATA is set then the DATADIRECTORY can be omitted.

 e.g
 
postgres@tardis:~/tempdata$ export PGDATA=`pwd`
postgres@tardis:~/tempdata$ /usr/lib/postgresql/9.3/bin/initdb 
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_GB.UTF-8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /var/lib/postgresql/tempdata ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
creating configuration files ... ok
creating template1 database in /var/lib/postgresql/tempdata/base/1 ... ok
initializing pg_authid ... ok
initializing dependencies ... ok
creating system views ... ok
loading system objects' descriptions ... ok
creating collations ... ok
creating conversions ... ok
creating dictionaries ... ok
setting privileges on built-in objects ... ok
creating information schema ... ok
loading PL/pgSQL server-side language ... ok
vacuuming database template1 ... ok
copying template1 to template0 ... ok
copying template1 to postgres ... ok
syncing data to disk ... ok

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the option -A, or
--auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

    /usr/lib/postgresql/9.3/bin/postgres -D /var/lib/postgresql/tempdata
or
    /usr/lib/postgresql/9.3/bin/pg_ctl -D /var/lib/postgresql/tempdata -l 
logfile start

After initialising the data area initdb shows the two methods to start the database instance. The first one is useful for debugging and development purposes as starts the database directly from the command line without daemonising the process.

postgres@tardis:~/tempdata$ /usr/lib/postgresql/9.3/bin/postgres -D 
/var/lib/postgresql/tempdata
LOG:  database system was shut down at 2014-03-23 18:52:07 UTC
LOG:  database system is ready to accept connections
LOG:  autovacuum launcher started

To stop it simply press ctrl+c
The second method is more interesting as the PostgreSQL process managed as daemon via pg_ctl.
The option -l logfile is to enable the logfile redirection. Without this option the server's output will appear on the standard output.

without -l

postgres@tardis:~/tempdata$ /usr/lib/postgresql/9.3/bin/pg_ctl -D 
/var/lib/postgresql/tempdata  start
server starting
postgres@tardis:~/tempdata$ LOG:  database system was shut down at 2014-03-23 
19:00:36 UTC
LOG:  database system is ready to accept connections
LOG:  autovacuum launcher started

with -l 

postgres@tardis:~/tempdata$ /usr/lib/postgresql/9.3/bin/pg_ctl -D 
/var/lib/postgresql/tempdata -l logfile start
server starting

postgres@tardis:~/tempdata$ tail logfile 
LOG:  database system was shut down at 2014-03-23 19:01:19 UTC
LOG:  database system is ready to accept connections
LOG:  autovacuum launcher started

As seen in the subsection 3.1.2 pg_ctl accepts the command to perform on the cluster.
In order to stop the running instance simply running

postgres@tardis:~$ /usr/lib/postgresql/9.3/bin/pg_ctl -D 
/var/lib/postgresql/tempdata -l logfile stop
waiting for server to shut down.... done
server stopped