pg_dump

Extracts a database into a single script file or other archive file.

Synopsis

pg_dump [<connection_options>] [<dump_options>] <dbname>

pg_dump --help

pg_dump --version

where:

<connection_options> =
    [-h <host> | --host <host>] 
    [-p <port> | -- port <port>] 
    [-U <username> | --username <username>] 
    [-W | --password] 

<dump_options> =
    [-a | --data-only]
    [-b | --blobs]
    [-c | --clean]
    [-C | --create]
    [-d | --inserts]
    [(-D | --column-inserts) ]
    [-E <encoding> | --encoding <encoding>]
    [-f <file> | --file <file>]
    [-F(p|t|c)] | --format (plain|custom|tar)]
    [-i | --ignore-version]
    [-n <schema> | --schema <schema>]
    [-N <schema> | --exclude-schema <schema>]
    [-o | --oids]
    [-O | --no-owner]
    [-s | --schema-only]
    [-S <username> | --superuser <username>]
    [-t <table> | --table <table>]
    [-T <table> | --exclude-table <table>]
    [-v | --verbose]
    [(-x | --no-privileges) ]
    [--disable-dollar-quoting]
    [--disable-triggers]
    [--use-set-session-authorization]
    [--gp-syntax | --no-gp-syntax]
    [-Z <0..9> | --compress <0..9>]

Description

pg_dump is a standard PostgreSQL utility for backing up a database, and is also supported in HAWQ. It creates a single (non-parallel) dump file.

Use pg_dump if you are migrating your data to another database vendor’s system, or to another HAWQ system with a different segment configuration (for example, if the system you are migrating to has greater or fewer segment instances). To restore, you must use the corresponding pg_restore utility (if the dump file is in archive format), or you can use a client program such as psql (if the dump file is in plain text format).

Since pg_dump is compatible with regular PostgreSQL, it can be used to migrate data into HAWQ. The pg_dump utility in HAWQ is very similar to the PostgreSQL pg_dump utility, with the following exceptions and limitations:

  • If using pg_dump to backup a HAWQ database, keep in mind that the dump operation can take a long time (several hours) for very large databases. Also, you must make sure you have sufficient disk space to create the dump file.
  • If you are migrating data from one HAWQ system to another, use the --gp-syntax command-line option to include the DISTRIBUTED BY clause in CREATE TABLE statements. This ensures that HAWQ table data is distributed with the correct distribution key columns upon restore.

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).

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_restorecan 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. It can be manipulated with standard UNIX tools such as tar.

Options

<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.

<dump_options>

-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
Adds commands to the text output file to clean (DROP) database objects prior to (the commands for) creating them. Note that objects are not dropped before the dump operation begins, but DROP commands are added to the DDL dump output files so that when you use those files to do a restore, the DROP commands are run prior to the CREATE commands. 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-based 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
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-based 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>
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>
Send output to the specified file. If this is omitted, the standard output is used.

-F(p|c|t), --format (plain|custom|tar)
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 HAWQ (or PostgreSQL). However, some older versions might not be supported. Use this option if you need to override the version check.

-n, --schema <schema>
Dump only schemas matching the schema pattern; 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, 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, --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 specified multiple times to exclude schemas that match several different patterns. When both -n and -N are specified, the behavior is to dump only schemas that match at least one -n switch but no -N switches. If -N appears without -n, then schemas matching -N are excluded from an otherwise normal dump.

-o, --oids
Dump object identifiers (OIDs) as part of the data for every table. Use of this option is not recommended for files that are intended to be restored into HAWQ.

-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.

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

-S, --superuser <username>
Specify the superuser user name to use when disabling triggers. This is only relevant if --disable-triggers is used. It is better to leave this out, and instead start the resulting script as a superuser.

Note: HAWQ does not support user-defined triggers.

-t, --table <table>
Dump only tables (or views or sequences) matching the table pattern. Specify the table in the format schema.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, 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. Also, -t cannot be used to specify a child table partition. To dump a partitioned table, you must specify the parent table name.

-T, --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
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 triggers on the tables that you do not want to invoke during data reload. 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.

Note: HAWQ does not support user-defined triggers.

--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. A dump using SET SESSION AUTHORIZATION will require superuser privileges to restore correctly, whereas ALTER OWNER requires lesser privileges.

--gp-syntax | --no-gp-syntax
Use --gp-syntax to dump HAWQ syntax in the CREATE TABLE statements. This allows the distribution policy (DISTRIBUTED BY or DISTRIBUTED RANDOMLY clauses) of a HAWQ table to be dumped, which is useful for restoring into other HAWQ systems. The default is to include HAWQ syntax when connected to a HAWQ system, and to exclude it when connected to a regular PostgreSQL system.

-Z, --compress 0..9
Specify the compression level to use in archive formats that support compression. Currently only the custom archive format supports compression.

<connection_options>

-h, --host <host>
The host name of the machine on which the HAWQ master database server is running. If not specified, reads from the environment variable PGHOST or defaults to localhost.

-p, --port <port>
The TCP port on which the HAWQ master database server is listening for connections. If not specified, reads from the environment variable PGPORT or defaults to 5432.

-U, --username <username>
The database role name to connect as. If not specified, reads from the environment variable PGUSER or defaults to the current system role name.

-W, --password
Force a password prompt.

Other Options

--help
Displays the online help.

--version
Displays the version of this utility.

Notes

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.

Examples

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

Dump a HAWQ in tar file format and include distribution policy information:

$ pg_dump -Ft --gp-syntax mydb > db.tar

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

Note: A warning related to the gp_enable_column_oriented_table parameter may appear. If it does, disregard it.

To dump a single table named mytab:

$ pg_dump -t mytab 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. 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

See Also

pg_dumpall, pg_restore, psql