pg_dump is a utility for saving a PostgreSQL database into a script or an archive file. The script files are in plain-text format and contain the SQL commands required to reconstruct the database to the state it was in at the time it was saved. They can be used to reconstruct the database even on other machines and other architectures, with some modifications even on other RDBMS products. Furthermore, there are alternative archive file formats that are meant to be used with pg_restore to rebuild the database, and they also allow pg_restore to be selective about what is restored, or even to reorder the items prior to being restored. The archive files are also designed to be portable across architectures.
pg_dump will save the information necessary to re-generate all user-defined types, functions, tables, indexes, aggregates, and operators. In addition, all the data is copied out in text format so that it can be readily copied in again, as well as imported into tools for editing.
pg_dump is useful for dumping out the contents of a database to move from one PostgreSQL installation to another.
When used with one of the archive file formats and combined with pg_restore , pg_dump provides a flexible archival and transfer mechanism. pg_dump can be used to backup an entire database, then pg_restore can be used to examine the archive and/or select which parts of the database are to be restored. The most flexible output file format is the "custom" format (-Fc). It allows for selection and reordering of all archived items, and is compressed by default. The tar format (-Ft) is not compressed and it is not possible to reorder data when loading, but it is otherwise quite flexible; moreover, it can be manipulated with other tools such as tar.
While running pg_dump, one should examine the output for any warnings (printed on standard error), especially in light of the limitations listed below.
pg_dump makes consistent backups even if the database is being used concurrently. pg_dump does not block other users accessing the database (readers or writers).
pg_dump accepts the following command line arguments. (Long option forms are only available on some platforms.)
Specifies the name of the database to be dumped.
Dump only the data, not the schema (data definitions).
This option is only meaningful for the plain-text format. For the other formats, you may specify the option when you call pg_restore.
Include large objects in dump.
Output commands to clean (drop) database objects prior to (the commands for) creating them.
This option is only meaningful for the plain-text format. For the other formats, you may specify the option when you call pg_restore.
Begin the output with a command to create the database itself and reconnect to the created database. (With a script of this form, it doesn't matter which database you connect to before running the script.)
This option is only meaningful for the plain-text format. For the other formats, you may specify the option when you call pg_restore.
Dump data as INSERT commands (rather than COPY). This will make restoration very slow, but it makes the archives more portable to other RDBMS packages.
Dump data as INSERT commands with explicit column names (INSERT INTO table (column, ...) VALUES ...). This will make restoration very slow, but it is necessary if you desire to rearrange column ordering.
Send output to the specified file. If this is omitted, the standard output is used.
Selects the format of the output. format can be one of the following:
Output a plain-text SQL script file (default)
Output a tar archive suitable for input into pg_restore. Using this archive format allows reordering and/or exclusion of schema elements at the time the database is restored. It is also possible to limit which data is reloaded at restore time.
Output a custom archive suitable for input into pg_restore. This is the most flexible format in that it allows reordering of data load as well as schema elements. This format is also compressed by default.
Ignore version mismatch between pg_dump and the database server. Since pg_dump knows a great deal about system catalogs, any given version of pg_dump is only intended to work with the corresponding release of the database server. Use this option if you need to override the version check (and if pg_dump then fails, don't say you weren't warned).
Suppress double quotes around identifiers unless absolutely necessary. This may cause trouble loading this dumped data if there are reserved words used for identifiers. This was the default behavior for pg_dump prior to version 6.4.
Include double quotes around identifiers. This is the default.
Dump object identifiers (OIDs) for every table. Use this option if your application references the OID columns in some way (e.g., in a foreign key constraint). Otherwise, this option should not be used.
Do not output commands to set the object ownership to match the original database. Typically, pg_dump issues (psql-specific) \connect statements to set ownership of schema elements. See also under -R and -X use-set-session-authorization. Note that -O does not prevent all reconnections to the database, only the ones that are exclusively used for ownership adjustments.
This option is only meaningful for the plain-text format. For the other formats, you may specify the option when you call pg_restore.
Prohibit pg_dump from outputting a script that would require reconnections to the database while being restored. An average restoration script usually has to reconnect several times as different users to set the original ownerships of the objects. This option is a rather blunt instrument because it makes pg_dump lose this ownership information, unless you use the -X use-set-session-authorization option.
One possible reason why reconnections during restore might not be desired is if the access to the database requires manual interaction (e.g., passwords).
This option is only meaningful for the plain-text format. For the other formats, you may specify the option when you call pg_restore.
Dump only the schema (data definitions), no data.
The scripts or archives created by pg_dump need to have superuser access in certain cases, such as when disabling triggers or setting ownership of schema elements. This option specifies the user name to use for those cases.
Dump data for table only.
Specifies verbose mode.
Prevent dumping of access privileges (grant/revoke commands).
Normally, if a (plain-text mode) script generated by pg_dump must alter the current database user (e.g., to set correct object ownerships), it uses the psql \connect command. This command actually opens a new connection, which might require manual interaction (e.g., passwords). If you use the -X use-set-session-authorization option, then pg_dump will instead output SET SESSION AUTHORIZATION commands. This has the same effect, but it requires that the user restoring the database from the generated script be a database superuser. This option effectively overrides the -R option.
Since SET SESSION AUTHORIZATION is a standard SQL command, whereas \connect only works in psql, this option also enhances the theoretical portability of the output script.
This option is only meaningful for the plain-text format. For the other formats, you may specify the option when you call pg_restore.
Specify the compression level to use in archive formats that support compression (currently only the custom archive format supports compression).
pg_dump also accepts the following command line arguments for connection parameters:
Specifies the host name of the machine on which the server is running. If host begins with a slash, it is used as the directory for the Unix domain socket.
Specifies the Internet TCP/IP port or local Unix domain socket file extension on which the server is listening for connections. The port number defaults to 5432, or the value of the PGPORT environment variable (if set).
Connect as the given user.
Force a password prompt. This should happen automatically if the server requires password authentication.
Connection to database 'template1' failed.
connectDBStart() -- connect() failed: No such file or directory
Is the postmaster running locally
and accepting connections on Unix socket '/tmp/.s.PGSQL.5432'?pg_dump could not attach to the postmaster process on the specified host and port. If you see this message, ensure that the postmaster is running on the proper host and that you have specified the proper port.
Note: pg_dump internally executes SELECT statements. If you have problems running pg_dump, make sure you are able to select information from the database using, for example, psql.
If your installation has any local additions to the template1 database, be careful to restore the output of pg_dump into a truly empty database; otherwise you are likely to get errors due to duplicate definitions of the added objects. To make an empty database without any local additions, copy from template0 not template1, for example:
CREATE DATABASE foo WITH TEMPLATE = template0;
pg_dump has a few limitations:
When dumping a single table or as plain text, pg_dump does not handle large objects. Large objects must be dumped in their entirety using one of the binary archive formats.
When doing a data only dump, pg_dump emits queries to disable triggers on user tables before inserting the data and queries to re-enable them after the data has been inserted. If the restore is stopped in the middle, the system catalogs may be left in the wrong state.
To dump a database:
$ pg_dump mydb > db.out
To reload this database:
$ psql -d database -f db.out
To dump a database called mydb that contains large objects to a tar file:
$ pg_dump -Ft -b mydb > db.tar
To reload this database (with large objects) to an existing database called newdb:
$ pg_restore -d newdb db.tar