mirror of https://github.com/postgres/postgres
Split management chapter from start-ag.sgml to manage-ag.sgml.REL6_5_PATCHES
Thomas G. Lockhart
27 years ago
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<chapter id="manage-ag"> |
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<title>Managing a Database</title> |
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|
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<para> |
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If the <productname>Postgres</productname> |
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<application>postmaster</application> is up and running we can create |
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some databases to experiment with. Here, we describe the |
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basic commands for managing a database. |
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</para> |
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|
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<sect1> |
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<title>Creating a Database</title> |
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<para> |
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Let's say you want to create a database named mydb. |
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You can do this with the following command: |
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<programlisting> |
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% createdb <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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|
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<productname>Postgres</productname> allows you to create |
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any number of databases |
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at a given site and you automatically become the |
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database administrator of the database you just created. |
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Database names must have an alphabetic first |
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character and are limited to 16 characters in length. |
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Not every user has authorization to become a database |
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administrator. If <productname>Postgres</productname> |
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refuses to create databases |
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for you, then the site administrator needs to grant you |
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permission to create databases. Consult your site |
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administrator if this occurs. |
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</para> |
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</sect1> |
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|
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<sect1> |
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<title>Accessing a Database</title> |
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<para> |
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Once you have constructed a database, you can access it |
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by: |
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|
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<itemizedlist spacing="compact" mark="bullet"> |
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<listitem> |
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<para> |
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running the <productname>Postgres</productname> terminal monitor program |
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(<application>psql</application>) which allows you to interactively |
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enter, edit, and execute <acronym>SQL</acronym> commands. |
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</para> |
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</listitem> |
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|
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<listitem> |
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<para> |
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writing a C program using the <literal>libpq</literal> subroutine |
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library. This allows you to submit <acronym>SQL</acronym> commands |
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from C and get answers and status messages back to |
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your program. This interface is discussed further |
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in the <citetitle>PostgreSQL Programmer's Guide</citetitle>. |
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</para> |
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</listitem> |
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</itemizedlist> |
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|
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You might want to start up <application>psql</application>, |
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to try out the examples in this manual. It can be activated for the |
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<replaceable class="parameter">dbname</replaceable> database by typing the command: |
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|
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<programlisting> |
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% psql <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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|
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You will be greeted with the following message: |
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|
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<programlisting> |
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Welcome to the Postgres interactive sql monitor: |
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type \? for help on slash commands |
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type \q to quit |
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type \g or terminate with semicolon to execute query |
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You are currently connected to the database: <replaceable>dbname</replaceable> |
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<replaceable>dbname</replaceable>=> |
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</programlisting> |
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</para> |
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<para> |
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This prompt indicates that the terminal monitor is listening |
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to you and that you can type <acronym>SQL</acronym> queries into a |
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workspace maintained by the terminal monitor. |
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The <application>psql</application> program responds to escape |
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codes that begin |
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with the backslash character, "\". For example, you |
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can get help on the syntax of various |
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<productname>Postgres</productname> <acronym>SQL</acronym> commands by typing: |
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|
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<programlisting> |
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<replaceable>dbname</replaceable>=> \h |
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</programlisting> |
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|
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Once you have finished entering your queries into the |
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workspace, you can pass the contents of the workspace |
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to the <productname>Postgres</productname> server by typing: |
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|
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<programlisting> |
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<replaceable>dbname</replaceable>=> \g |
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</programlisting> |
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|
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This tells the server to process the query. If you |
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terminate your query with a semicolon, the backslash-g is not |
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necessary. <application>psql</application> will automatically |
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process semicolon terminated queries. |
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To read queries from a file, instead of |
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entering them interactively, type: |
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|
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<programlisting> |
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<replaceable>dbname</replaceable>=> \i <replaceable class="parameter">filename</replaceable> |
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</programlisting> |
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|
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To get out of <application>psql</application> and return to UNIX, type |
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|
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<programlisting> |
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<replaceable>dbname</replaceable>=> \q |
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</programlisting> |
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|
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and <application>psql</application> will quit and return |
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you to your command shell. (For more escape codes, type |
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backslash-h at the monitor prompt.) |
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White space (i.e., spaces, tabs and newlines) may be |
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used freely in <acronym>SQL</acronym> queries. |
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Single-line comments are denoted by two dashes |
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(<quote>--</quote>). Everything after the dashes up to the end of the |
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line is ignored. Multiple-line comments, and comments within a line, |
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are denoted by <quote>/* ... */</quote>, a convention borrowed |
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from <productname>Ingres</productname>. |
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</para> |
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</sect1> |
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|
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<sect1> |
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<title>Destroying a Database</title> |
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<para> |
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If you are the database administrator for the database |
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mydb, you can destroy it using the following UNIX command: |
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<programlisting> |
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% destroydb <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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|
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This action physically removes all of the UNIX files |
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associated with the database and cannot be undone, so |
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this should only be done with a great deal of forethought. |
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</para> |
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|
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<para> |
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It is also possible to destroy a database from within an |
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<acronym>SQL</acronym> session by using |
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|
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<programlisting> |
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> drop database <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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</para> |
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</sect1> |
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|
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<sect1> |
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<title>Backup and Restore</title> |
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<caution> |
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<para> |
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Every database should be backed up on a regular basis. Since |
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<productname>Postgres</productname> manages it's own files in the |
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file system, it is <emphasis>not advisable</emphasis> to rely on |
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system backups of your file system for your database backups; |
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there is no guarantee that the files will be in a usable, |
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consistant state after restoration. |
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</para> |
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</caution> |
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|
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<para> |
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<productname>Postgres</productname> provides two utilities to |
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backup your system: <application>pg_dump</application> to backup |
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individual databases and |
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<application>pg_dumpall</application> to backup your installation |
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in one step. |
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</para> |
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|
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<para> |
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An individual database can be backed up using the following |
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command: |
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|
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<programlisting> |
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% pg_dump <replaceable class="parameter">dbname</replaceable> > <replaceable class="parameter">dbname</replaceable>.pgdump |
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</programlisting> |
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and can be restored using |
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<programlisting> |
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cat <replaceable class="parameter">dbname</replaceable>.pgdump | psql <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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</para> |
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|
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<para> |
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This technique can be used to move databases to new |
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locations, and to rename existing databases. |
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</para> |
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|
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<sect2> |
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<title>Large Databases</title> |
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|
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<note> |
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<title>Author</title> |
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<para> |
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Written by <ulink url="hannu@trust.ee">Hannu Krosing</ulink> on |
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1999-06-19. |
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</para> |
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</note> |
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|
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<para> |
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Since <productname>Postgres</productname> allows tables larger |
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than the maximum file size on your system, it can be problematic |
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to dump the table to a file, since the resulting file will likely |
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be larger than the maximum size allowed by your system.</para> |
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|
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<para> |
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As <application>pg_dump</application> writes to stdout, |
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you can just use standard *nix tools |
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to work around this possible problem: |
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|
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<itemizedlist> |
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<listitem> |
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<para> |
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Use compressed dumps: |
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|
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<programlisting> |
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% pg_dump <replaceable class="parameter">dbname</replaceable> | gzip > <replaceable class="parameter">filename</replaceable>.dump.gz |
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</programlisting> |
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reload with |
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|
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<programlisting> |
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% createdb <replaceable class="parameter">dbname</replaceable> |
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% gunzip -c <replaceable class="parameter">filename</replaceable>.dump.gz | psql <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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or |
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<programlisting> |
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% cat <replaceable class="parameter">filename</replaceable>.dump.gz | gunzip | psql <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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</para> |
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</listitem> |
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|
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<listitem> |
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<para> |
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Use split: |
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<programlisting> |
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% pg_dump <replaceable class="parameter">dbname</replaceable> | split -b 1m - <replaceable class="parameter">filename</replaceable>.dump. |
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</programlisting> |
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reload with |
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<programlisting> |
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% createdb <replaceable class="parameter">dbname</replaceable> |
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% cat <replaceable class="parameter">filename</replaceable>.dump.* | pgsql <replaceable class="parameter">dbname</replaceable> |
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</programlisting> |
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</para> |
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</listitem> |
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</itemizedlist> |
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</para> |
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|
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<para> |
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Of course, the name of the file |
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(<replaceable class="parameter">filename</replaceable>) and the |
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content of the <application>pg_dump</application> output need not |
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match the name of the database. Also, the restored database can |
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have an arbitrary new name, so this mechanism is also suitable |
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for renaming databases. |
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</sect2> |
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</sect1> |
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</chapter> |
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|
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<!-- Keep this comment at the end of the file |
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Local variables: |
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mode: sgml |
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sgml-omittag:nil |
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sgml-shorttag:t |
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sgml-minimize-attributes:nil |
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sgml-always-quote-attributes:t |
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sgml-indent-step:1 |
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sgml-indent-data:t |
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sgml-parent-document:nil |
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sgml-default-dtd-file:"./reference.ced" |
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sgml-exposed-tags:nil |
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sgml-local-catalogs:"/usr/lib/sgml/CATALOG" |
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sgml-local-ecat-files:nil |
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End: |
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--> |
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