Movatterモバイル変換

Before you can do anything, you must initialize a database storage area on disk. We call this adatabase cluster. (TheSQL standard uses the term catalog cluster.) A database cluster is a collection of databases that is managed by a single instance of a running database server. After initialization, a database cluster will contain a database namedpostgres, which is meant as a default database for use by utilities, users and third party applications. The database server itself does not require thepostgres database to exist, but many external utility programs assume it exists. There are two more databases created within each cluster during initialization, namedtemplate1 andtemplate0. As the names suggest, these will be used as templates for subsequently-created databases; they should not be used for actual work. (SeeChapter 21 for information about creating new databases within a cluster.)

In file system terms, a database cluster is a single directory under which all data will be stored. We call this thedata directory ordata area. It is completely up to you where you choose to store your data. There is no default, although locations such as/usr/local/pgsql/data or/var/lib/pgsql/data are popular. The data directory must be initialized before being used, using the programinitdb which is installed withPostgres Pro.

If you are using a pre-packaged version ofPostgreSQL, it may well have a specific convention for where to place the data directory, and it may also provide a script for creating the data directory. In that case you should use that script in preference to runninginitdb directly. Consult the package-level documentation for details.

To initialize a database cluster manually, runinitdb and specify the desired file system location of the database cluster with the-D option, for example:

$initdb -D /usr/local/pgsql/data

Note that you must execute this command while logged into thePostgres Pro user account, which is described in the previous section.

Alternatively, you can runinitdb via thepg_ctl program like so:

$pg_ctl -D /usr/local/pgsql/data initdb

This may be more intuitive if you are usingpg_ctl for starting and stopping the server (seeSection 17.3), so thatpg_ctl would be the sole command you use for managing the database server instance.

initdb will attempt to create the directory you specify if it does not already exist. Of course, this will fail ifinitdb does not have permissions to write in the parent directory. It's generally recommendable that thePostgres Pro user own not just the data directory but its parent directory as well, so that this should not be a problem. If the desired parent directory doesn't exist either, you will need to create it first, using root privileges if the grandparent directory isn't writable. So the process might look like this:

root#mkdir /usr/local/pgsqlroot#chown postgres /usr/local/pgsqlroot#su postgrespostgres$initdb -D /usr/local/pgsql/data

initdb will refuse to run if the data directory exists and already contains files; this is to prevent accidentally overwriting an existing installation.

Because the data directory contains all the data stored in the database, it is essential that it be secured from unauthorized access.initdb therefore revokes access permissions from everyone but thePostgres Pro user, and optionally, group. Group access, when enabled, is read-only. This allows an unprivileged user in the same group as the cluster owner to take a backup of the cluster data or perform other operations that only require read access.

Note that enabling or disabling group access on an existing cluster requires the cluster to be shut down and the appropriate mode to be set on all directories and files before restartingPostgres Pro. Otherwise, a mix of modes might exist in the data directory. For clusters that allow access only by the owner, the appropriate modes are0700 for directories and0600 for files. For clusters that also allow reads by the group, the appropriate modes are0750 for directories and0640 for files.

However, while the directory contents are secure, the default client authentication setup allows any local user to connect to the database and even become the database superuser. If you do not trust other local users, we recommend you use one ofinitdb's-W,--pwprompt or--pwfile options to assign a password to the database superuser. Also, specify-A scram-sha-256 so that the defaulttrust authentication mode is not used; or modify the generatedpg_hba.conf file after runninginitdb, butbefore you start the server for the first time. (Other reasonable approaches include usingpeer authentication or file system permissions to restrict connections. SeeChapter 19 for more information.)

initdb also initializes the default locale for the database cluster. Normally, it will just take the locale settings in the environment and apply them to the initialized database. It is possible to specify a different locale for the database; more information about that can be found inSection 22.1. The default sort order used within the particular database cluster is set byinitdb, and while you can create new databases using different sort order, the order used in the template databases that initdb creates cannot be changed without dropping and recreating them. There is also a performance impact for using locales other thanC orPOSIX. Therefore, it is important to make this choice correctly the first time.

initdb also sets the default character set encoding for the database cluster. Normally this should be chosen to match the locale setting. For details seeSection 22.3.

Non-C and non-POSIX locales rely on the operating system's collation library for character set ordering. This controls the ordering of keys stored in indexes. For this reason, a cluster cannot switch to an incompatible collation library version, either through snapshot restore, binary streaming replication, a different operating system, or an operating system upgrade.