pg_dump - Online in the Cloud

PROGRAM:

NAME

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

SYNOPSIS

pg_dump [connection-option...] [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).

pg_dump only dumps a single database. To backup global objects that are common to all
databases in a cluster, such as roles and tablespaces, use pg_dumpall(1).

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(1). 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(1) 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 formats are the
“custom” format (-Fc) and the “directory” format(-Fd). They allow for selection and
reordering of all archived items, support parallel restoration, and are compressed by
default. The “directory” format is the only format that supports parallel dumps.

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). Table data, large objects, and
sequence values are dumped.

This option is similar to, but for historical reasons not identical to, specifying
--section=data.

-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 outputting the commands for
creating them. (Unless --if-exists is also specified, restore might generate some
harmless error messages, if any objects were not present in the destination database.)

This option is only meaningful for the plain-text format. For the archive formats, you
can 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 in the
destination installation you connect to before running the script.) If --clean is also
specified, the script drops and recreates the target database before reconnecting to
it.

This option is only meaningful for the plain-text format. For the archive formats, you
can specify the option when you call pg_restore.

-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. This parameter can be omitted for file based output
formats, in which case the standard output is used. It must be given for the directory
output format however, where it specifies the target directory instead of a file. In
this case the directory is created by pg_dump and must not exist before.

-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-format archive suitable for input into pg_restore. Together with
the directory output format, this is the most flexible output format in that it
allows manual selection and reordering of archived items during restore. This
format is also compressed by default.

d
directory
Output a directory-format archive suitable for input into pg_restore. This will
create a directory with one file for each table and blob being dumped, plus a
so-called Table of Contents file describing the dumped objects in a
machine-readable format that pg_restore can read. A directory format archive can
be manipulated with standard Unix tools; for example, files in an uncompressed
archive can be compressed with the gzip tool. This format is compressed by default
and also supports parallel dumps.

t
tar
Output a tar-format archive suitable for input into pg_restore. The tar format is
compatible with the directory format: extracting a tar-format archive produces a
valid directory-format archive. However, the tar format does not support
compression. Also, when using tar format the relative order of table data items
cannot be changed during restore.

-j njobs
--jobs=njobs
Run the dump in parallel by dumping njobs tables simultaneously. This option reduces
the time of the dump but it also increases the load on the database server. You can
only use this option with the directory output format because this is the only output
format where multiple processes can write their data at the same time.

pg_dump will open njobs + 1 connections to the database, so make sure your
max_connections setting is high enough to accommodate all connections.

Requesting exclusive locks on database objects while running a parallel dump could
cause the dump to fail. The reason is that the pg_dump master process requests shared
locks on the objects that the worker processes are going to dump later in order to
make sure that nobody deletes them and makes them go away while the dump is running.
If another client then requests an exclusive lock on a table, that lock will not be
granted but will be queued waiting for the shared lock of the master process to be
released. Consequently any other access to the table will not be granted either and
will queue after the exclusive lock request. This includes the worker process trying
to dump the table. Without any precautions this would be a classic deadlock situation.
To detect this conflict, the pg_dump worker process requests another shared lock using
the NOWAIT option. If the worker process is not granted this shared lock, somebody
else must have requested an exclusive lock in the meantime and there is no way to
continue with the dump, so pg_dump has no choice but to abort the dump.

For a consistent backup, the database server needs to support synchronized snapshots,
a feature that was introduced in PostgreSQL 9.2. With this feature, database clients
can ensure they see the same data set even though they use different connections.
pg_dump -j uses multiple database connections; it connects to the database once with
the master process and once again for each worker job. Without the synchronized
snapshot feature, the different worker jobs wouldn't be guaranteed to see the same
data in each connection, which could lead to an inconsistent backup.

If you want to run a parallel dump of a pre-9.2 server, you need to make sure that the
database content doesn't change from between the time the master connects to the
database until the last worker job has connected to the database. The easiest way to
do this is to halt any data modifying processes (DDL and DML) accessing the database
before starting the backup. You also need to specify the --no-synchronized-snapshots
parameter when running pg_dump -j against a pre-9.2 PostgreSQL server.

-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; see EXAMPLES.

Note
When -n is specified, pg_dump makes no attempt to dump any other database objects
that the selected schema(s) might 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
can 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.

This option is the inverse of --data-only. It is similar to, but for historical
reasons not identical to, specifying --section=pre-data --section=post-data.

(Do not confuse this with the --schema option, which uses the word “schema” in a
different meaning.)

To exclude table data for only a subset of tables in the database, see
--exclude-table-data.

-S username
--superuser=username
Specify the superuser user name to use when disabling triggers. This is relevant only
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 or foreign tables) 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; see EXAMPLES.

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) might 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.

-V
--version
Print the pg_dump version and exit.

-x
--no-privileges
--no-acl
Prevent dumping of access privileges (grant/revoke commands).

-Z 0..9
--compress=0..9
Specify the compression level to use. Zero means no compression. For the custom
archive format, this specifies compression of individual table-data segments, and the
default is to compress at a moderate level. For plain text output, setting a nonzero
compression level causes the entire output file to be compressed, as though it had
been fed through gzip; but the default is not to compress. The tar archive format
currently does not support compression at all.

--binary-upgrade
This option is for use by in-place upgrade utilities. Its use for other purposes is
not recommended or supported. The behavior of the option may change in future releases
without notice.

--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. However, 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.

--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 relevant only 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
can specify the option when you call pg_restore.

--enable-row-security
This option is relevant only when dumping the contents of a table which has row
security. By default, pg_dump will set row_security to off, to ensure that all data is
dumped from the table. If the user does not have sufficient privileges to bypass row
security, then an error is thrown. This parameter instructs pg_dump to set
row_security to on instead, allowing the user to dump the parts of the contents of the
table that they have access to.

--exclude-table-data=table
Do not dump data for any tables matching the table pattern. The pattern is interpreted
according to the same rules as for -t. --exclude-table-data can be given more than
once to exclude tables matching any of several patterns. This option is useful when
you need the definition of a particular table even though you do not need the data in
it.

To exclude data for all tables in the database, see --schema-only.

--if-exists
Use conditional commands (i.e. add an IF EXISTS clause) when cleaning database
objects. This option is not valid unless --clean is also specified.

--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.
However, 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 might fail altogether if you have rearranged column order. The
--column-inserts option is safe against column order changes, though even slower.

--lock-wait-timeout=timeout
Do not wait forever to acquire shared table locks at the beginning of the dump.
Instead fail if unable to lock a table within the specified timeout. The timeout may
be specified in any of the formats accepted by SET statement_timeout. (Allowed values
vary depending on the server version you are dumping from, but an integer number of
milliseconds is accepted by all versions since 7.3. This option is ignored when
dumping from a pre-7.3 server.)

--no-security-labels
Do not dump security labels.

--no-synchronized-snapshots
This option allows running pg_dump -j against a pre-9.2 server, see the documentation
of the -j parameter for more details.

--no-tablespaces
Do not output commands to select tablespaces. With this option, all objects will be
created in whichever tablespace is the default during restore.

This option is only meaningful for the plain-text format. For the archive formats, you
can specify the option when you call pg_restore.

--no-unlogged-table-data
Do not dump the contents of unlogged tables. This option has no effect on whether or
not the table definitions (schema) are dumped; it only suppresses dumping the table
data. Data in unlogged tables is always excluded when dumping from a standby server.

--quote-all-identifiers
Force quoting of all identifiers. This may be useful when dumping a database for
migration to a future version that may have introduced additional keywords.

--section=sectionname
Only dump the named section. The section name can be pre-data, data, or post-data.
This option can be specified more than once to select multiple sections. The default
is to dump all sections.

The data section contains actual table data, large-object contents, and sequence
values. Post-data items include definitions of indexes, triggers, rules, and
constraints other than validated check constraints. Pre-data items include all other
data definition items.

--serializable-deferrable
Use a serializable transaction for the dump, to ensure that the snapshot used is
consistent with later database states; but do this by waiting for a point in the
transaction stream at which no anomalies can be present, so that there isn't a risk of
the dump failing or causing other transactions to roll back with a
serialization_failure. See Chapter 13, Concurrency Control, in the documentation for
more information about transaction isolation and concurrency control.

This option is not beneficial for a dump which is intended only for disaster recovery.
It could be useful for a dump used to load a copy of the database for reporting or
other read-only load sharing while the original database continues to be updated.
Without it the dump may reflect a state which is not consistent with any serial
execution of the transactions eventually committed. For example, if batch processing
techniques are used, a batch may show as closed in the dump without all of the items
which are in the batch appearing.

This option will make no difference if there are no read-write transactions active
when pg_dump is started. If read-write transactions are active, the start of the dump
may be delayed for an indeterminate length of time. Once running, performance with or
without the switch is the same.

--snapshot=snapshotname
Use the specified synchronized snapshot when making a dump of the database (see
Table 9.71, “Snapshot Synchronization Functions” for more details).

This option is useful when needing to synchronize the dump with a logical replication
slot (see Chapter 46, Logical Decoding, in the documentation) or with a concurrent
session.

In the case of a parallel dump, the snapshot name defined by this option is used
rather than taking a new snapshot.

--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, might not restore properly. Also,
a dump using SET SESSION AUTHORIZATION will certainly require superuser privileges to
restore correctly, whereas ALTER OWNER requires lesser privileges.

-?
--help
Show help about pg_dump command line arguments, and exit.

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

-d dbname
--dbname=dbname
Specifies the name of the database to connect to. This is equivalent to specifying
dbname as the first non-option argument on the command line.

If this parameter contains an = sign or starts with a valid URI prefix (postgresql://
or postgres://), it is treated as a conninfo string. See Section 31.1, “Database
Connection Control Functions”, in the documentation for more information.

-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
--username=username
User name to connect as.

-w
--no-password
Never issue a password prompt. If the server requires password authentication and a
password is not available by other means such as a .pgpass file, the connection
attempt will fail. This option can be useful in batch jobs and scripts where no user
is present to enter a password.

-W
--password
Force pg_dump to prompt for a password before connecting to a database.

This option is never essential, since pg_dump will automatically prompt for a password
if the server demands password authentication. However, pg_dump will waste a
connection attempt finding out that the server wants a password. In some cases it is
worth typing -W to avoid the extra connection attempt.

--role=rolename
Specifies a role name to be used to create the dump. This option causes pg_dump to
issue a SET ROLE rolename command after connecting to the database. It is useful when
the authenticated user (specified by -U) lacks privileges needed by pg_dump, but can
switch to a role with the required rights. Some installations have a policy against
logging in directly as a superuser, and use of this option allows dumps to be made
without violating the policy.

ENVIRONMENT

PGDATABASE
PGHOST
PGOPTIONS
PGPORT
PGUSER
Default connection parameters.

This utility, like most other PostgreSQL utilities, also uses the environment variables
supported by libpq (see Section 31.14, “Environment Variables”, in the documentation).

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(1).
Also, any default connection settings and environment variables used by the libpq
front-end library will apply.

The database activity of pg_dump is normally collected by the statistics collector. If
this is undesirable, you can set parameter track_counts to false via PGOPTIONS or the
ALTER USER command.

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;

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 then commands
to re-enable them after the data has been inserted. If the restore is stopped in the
middle, the system catalogs might be left in the wrong state.

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 optimal performance; see Section 23.1.3, “Updating Planner
Statistics”, in the documentation and Section 23.1.6, “The Autovacuum Daemon”, in the
documentation for more information. The dump file also does not contain any ALTER DATABASE
... SET commands; these settings are dumped by pg_dumpall(1), along with database users
and other installation-wide settings.

Because pg_dump is used to transfer data to newer versions of PostgreSQL, the output of
pg_dump can be expected to load into PostgreSQL server versions newer than pg_dump's
version. pg_dump can also dump from PostgreSQL servers older than its own version.
(Currently, servers back to version 7.0 are supported.) However, pg_dump cannot dump from
PostgreSQL servers newer than its own major version; it will refuse to even try, rather
than risk making an invalid dump. Also, it is not guaranteed that pg_dump's output can be
loaded into a server of an older major version — not even if the dump was taken from a
server of that version. Loading a dump file into an older server may require manual
editing of the dump file to remove syntax not understood by the older server.

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 dump a database into a directory-format archive:

$ pg_dump -Fd mydb -f dumpdir

To dump a database into a directory-format archive in parallel with 5 worker jobs:

$ pg_dump -Fd mydb -j 5 -f dumpdir

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

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