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13.10 pg_dump

Name

pg_dump -- extract a PostgreSQL database into a script file or other archive file

Synopsis

pg_dump [option...] [dbname]

Description

pg_dump is a utility for backing up a PostgreSQL database. It makes consistent backups even if the database is being used concurrently. pg_dump does not block other users accessing the database (readers or writers).

Dumps can be output in script or archive file formats. Script dumps are plain-text files containing the SQL commands required to reconstruct the database to the state it was in at the time it was saved. To restore from such a script, feed it to psql. Script files can be used to reconstruct the database even on other machines and other architectures; with some modifications even on other SQL database products.

The alternative archive file formats must be used with pg_restore to rebuild the database. They allow pg_restore to be selective about what is restored, or even to reorder the items prior to being restored. The archive file formats are designed to be portable across architectures.

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 standard Unix 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.

Options

The following command-line options control the content and format of the output.

dbname

Specifies the name of the database to be dumped. If this is not specified, the environment variable PGDATABASE is used. If that is not set, the user name specified for the connection is used.

-a

--data-only

Dump only the data, not the schema (data definitions). This option is only meaningful for the plain-text format. For the archive formats, you may specify the option when you call pg_restore.

-b

--blobs

Include large objects in the dump. This is the default behavior except when --schema, --table, or --schema-only is specified, so the -b switch is only useful to add large objects to selective dumps.

-c

--clean

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 archive formats, you may specify the option when you call pg_restore.

-C

--create

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 archive formats, you may specify the option when you call pg_restore.

-d

--inserts

Dump data as INSERT commands (rather than COPY). This will make restoration very slow; it is mainly useful for making dumps that can be loaded into non-PostgreSQL databases. Also, since this option generates a separate command for each row, an error in reloading a row causes only that row to be lost rather than the entire table contents. Note that the restore may fail altogether if you have rearranged column order. The -D option is safe against column order changes, though even slower.

-D

--column-inserts

--attribute-inserts

Dump data as INSERT commands with explicit column names (INSERT INTO table (column, ...) VALUES ...). This will make restoration very slow; it is mainly useful for making dumps that can be loaded into non-PostgreSQL databases. Also, since this option generates a separate command for each row, an error in reloading a row causes only that row to be lost rather than the entire table contents.

-E encoding

--encoding=encoding

Create the dump in the specified character set encoding. By default, the dump is created in the database encoding. (Another way to get the same result is to set the PGCLIENTENCODING environment variable to the desired dump encoding.)

-f file

--file=file

Send output to the specified file. If this is omitted, the standard output is used.

-F format

--format=format

Selects the format of the output. format can be one of the following:

p

plain

Output a plain-text SQL script file (the default).

c

custom

Output a custom archive suitable for input into pg_restore. This is the most flexible format in that it allows reordering of loading data as well as object definitions. This format is also compressed by default.

t

tar

Output a tar archive suitable for input into pg_restore. Using this archive format allows reordering and/or exclusion of database objects at the time the database is restored. It is also possible to limit which data is reloaded at restore time.

-i

--ignore-version

Ignore version mismatch between pg_dump and the database server. pg_dump can dump from servers running previous releases of PostgreSQL, but very old versions are not supported anymore (currently, those prior to 7.0). Dumping from a server newer than pg_dump is likely not to work at all. Use this option if you need to override the version check (and if pg_dump then fails, don't say you weren't warned).

-n schema

--schema=schema

Dump only schemas matching schema; this selects both the schema itself, and all its contained objects. When this option is not specified, all non-system schemas in the target database will be dumped. Multiple schemas can be selected by writing multiple -n switches. Also, the schema parameter is interpreted as a pattern according to the same rules used by psql's \d commands (see Patterns), so multiple schemas can also be selected by writing wildcard characters in the pattern. When using wildcards, be careful to quote the pattern if needed to prevent the shell from expanding the wildcards.

Note: When -n is specified, pg_dump makes no attempt to dump any other database objects that the selected schema(s) may depend upon. Therefore, there is no guarantee that the results of a specific-schema dump can be successfully restored by themselves into a clean database.

Note: Non-schema objects such as blobs are not dumped when -n is specified. You can add blobs back to the dump with the --blobs switch.

-N schema

--exclude-schema=schema

Do not dump any schemas matching the schema pattern. The pattern is interpreted according to the same rules as for -n. -N can be given more than once to exclude schemas matching any of several patterns. When both -n and -N are given, the behavior is to dump just the schemas that match at least one -n switch but no -N switches. If -N appears without -n, then schemas matching -N are excluded from what is otherwise a normal dump.

-o

--oids

Dump object identifiers (OIDs) as part of the data 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.

-O

--no-owner

Do not output commands to set ownership of objects to match the original database. By default, pg_dump issues ALTER OWNER or SET SESSION AUTHORIZATION statements to set ownership of created database objects. These statements will fail when the script is run unless it is started by a superuser (or the same user that owns all of the objects in the script). To make a script that can be restored by any user, but will give that user ownership of all the objects, specify -O. This option is only meaningful for the plain-text format. For the archive formats, you may specify the option when you call pg_restore.

-R

--no-reconnect

This option is obsolete but still accepted for backwards compatibility.

-s

--schema-only

Dump only the object definitions (schema), not data.

-S username

--superuser=username

Specify the superuser user name to use when disabling triggers. This is only relevant if --disable-triggers is used. (Usually, it's better to leave this out, and instead start the resulting script as superuser.)

-t table

--table=table

Dump only tables (or views or sequences) matching table. Multiple tables can be selected by writing multiple -t switches. Also, the table parameter is interpreted as a pattern according to the same rules used by psql's \d commands (see Patterns), so multiple tables can also be selected by writing wildcard characters in the pattern. When using wildcards, be careful to quote the pattern if needed to prevent the shell from expanding the wildcards. The -n and -N switches have no effect when -t is used, because tables selected by -t will be dumped regardless of those switches, and non-table objects will not be dumped.

Note: When -t is specified, pg_dump makes no attempt to dump any other database objects that the selected table(s) may depend upon. Therefore, there is no guarantee that the results of a specific-table dump can be successfully restored by themselves into a clean database.

Note: The behavior of the -t switch is not entirely upward compatible with pre-8.2 PostgreSQL versions. Formerly, writing -t tab would dump all tables named tab, but now it just dumps whichever one is visible in your default search path. To get the old behavior you can write -t '*.tab'. Also, you must write something like -t sch.tab to select a table in a particular schema, rather than the old locution of -n sch -t tab.

-T table

--exclude-table=table

Do not dump any tables matching the table pattern. The pattern is interpreted according to the same rules as for -t. -T can be given more than once to exclude tables matching any of several patterns. When both -t and -T are given, the behavior is to dump just the tables that match at least one -t switch but no -T switches. If -T appears without -t, then tables matching -T are excluded from what is otherwise a normal dump.

-v

--verbose

Specifies verbose mode. This will cause pg_dump to output detailed object comments and start/stop times to the dump file, and progress messages to standard error.

-x

--no-privileges

--no-acl

Prevent dumping of access privileges (grant/revoke commands).

--disable-dollar-quoting

This option disables the use of dollar quoting for function bodies, and forces them to be quoted using SQL standard string syntax.

--disable-triggers

This option is only relevant when creating a data-only dump. It instructs pg_dump to include commands to temporarily disable triggers on the target tables while the data is reloaded. Use this if you have referential integrity checks or other triggers on the tables that you do not want to invoke during data reload. Presently, the commands emitted for --disable-triggers must be done as superuser. So, you should also specify a superuser name with -S, or preferably be careful to start the resulting script as a superuser. This option is only meaningful for the plain-text format. For the archive formats, you may specify the option when you call pg_restore.

--use-set-session-authorization

Output SQL-standard SET SESSION AUTHORIZATION commands instead of ALTER OWNER commands to determine object ownership. This makes the dump more standards compatible, but depending on the history of the objects in the dump, may not restore properly. Also, a dump using SET SESSION AUTHORIZATION will certainly require superuser privileges to restore correctly, whereas ALTER OWNER requires lesser privileges.

-Z 0..9

--compress=0..9

Specify the compression level to use in archive formats that support compression. (Currently only the custom archive format supports compression.)

The following command-line options control the database connection parameters.

-h host

--host=host

Specifies the host name of the machine on which the server is running. If the value begins with a slash, it is used as the directory for the Unix domain socket. The default is taken from the PGHOST environment variable, if set, else a Unix domain socket connection is attempted.

-p port

--port=port

Specifies the TCP port or local Unix domain socket file extension on which the server is listening for connections. Defaults to the PGPORT environment variable, if set, or a compiled-in default.

-U username

Connect as the given user

-W

Force a password prompt. This should happen automatically if the server requires password authentication.

Environment

PGDATABASE

PGHOST

PGPORT

PGUSER

Default connection parameters.

Diagnostics

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.

Notes

If your database cluster 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 a data-only dump is chosen and the option --disable-triggers is used, pg_dump emits commands to disable triggers on user tables before inserting the data and commands 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.

Members of tar archives are limited to a size less than 8 GB. (This is an inherent limitation of the tar file format.) Therefore this format cannot be used if the textual representation of any one table exceeds that size. The total size of a tar archive and any of the other output formats is not limited, except possibly by the operating system.

The dump file produced by pg_dump does not contain the statistics used by the optimizer to make query planning decisions. Therefore, it is wise to run ANALYZE after restoring from a dump file to ensure good performance.

Because pg_dump is used to transfer data to newer versions of PostgreSQL, the output of pg_dump can be loaded into newer PostgreSQL databases. It also can read older PostgreSQL databases. However, it usually cannot read newer PostgreSQL databases or produce dump output that can be loaded into older database versions. To do this, manual editing of the dump file might be required.

Examples

To dump a database called mydb into a SQL-script file:

$ pg_dump mydb > db.sql

To reload such a script into a (freshly created) database named newdb:

$ psql -d newdb -f db.sql

To dump a database into a custom-format archive file:

$ pg_dump -Fc mydb > db.dump

To reload an archive file into a (freshly created) database named newdb:

$ pg_restore -d newdb db.dump

To dump a single table named mytab:

$ pg_dump -t mytab mydb > db.sql

To dump all tables whose names start with emp in the detroit schema, except for the table named employee_log:

$ pg_dump -t 'detroit.emp*' -T detroit.employee_log mydb > db.sql

To dump all schemas whose names start with east or west and end in gsm, excluding any schemas whose names contain the word test:

$ pg_dump -n 'east*gsm' -n 'west*gsm' -N '*test*' mydb > db.sql

The same, using regular expression notation to consolidate the switches:

$ pg_dump -n '(east|west)*gsm' -N '*test*' mydb > db.sql

To dump all database objects except for tables whose names begin with ts_:

$ pg_dump -T 'ts_*' mydb > db.sql

To specify an upper-case or mixed-case name in -t and related switches, you need to double-quote the name; else it will be folded to lower case (see Patterns). But double quotes are special to the shell, so in turn they must be quoted. Thus, to dump a single table with a mixed-case name, you need something like

$ pg_dump -t '"MixedCaseName"' mydb > mytab.sql

History

The pg_dump utility first appeared in Postgres95 release 0.02. The non-plain-text output formats were introduced in PostgreSQL release 7.1.

See Also

pg_dumpall, pg_restore, psql, Environment Variables ( Volume 2: Environment Variables)