pg_dump — extract a PostgreSQL™ database into a script file or other archive file
pg_dump
[connection-option
...] [option
...] [dbname
]
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(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.
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 and has a limit of 8 GB on the size of individual tables. Also, the relative order of table data items cannot be changed during restore.
-i
, --ignore-version
A deprecated option that is now ignored.
-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.
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.
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.
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.
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
). 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.
table
(column
, ...) VALUES
...
--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.
--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
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.
--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 the section called “Database Connection Control Functions” 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.
PGDATABASE
, PGHOST
, PGOPTIONS
, PGPORT
, PGUSER
Default connection parameters.
This utility, like most other PostgreSQL™ utilities, also uses the environment variables supported by libpq (see the section called “Environment Variables”).
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.
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.
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 optimal performance; see the section called “Updating Planner Statistics” and the section called “The Autovacuum Daemon” 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.
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