gs_dump

Background

gs_dump, provided by openGauss, is used to export database information. You can export a database or its objects (such as schemas, tables, and views). The database can be the default postgres database or a user-specified database.

gs_dump is executed by OS user omm.

When gs_dump is used to export data, other users can still access (read and write) openGauss databases.

gs_dump can export complete, consistent data. For example, if gs_dump is started to export database A at T1, data of the database at that time point will be exported, and modifications on the database after that time point will not be exported.

gs_dump can export database information to a plain-text SQL script file or archive file.

  • Plain-text SQL script: It contains the SQL statements required to restore the database. You can use gsql to execute the SQL script. With only a little modification, the SQL script can rebuild a database on other hosts or database products.
  • Archive file: It contains data required to restore the database. It can be a tar-, directory-, or custom-format archive. For details, see Table 1. The export result must be used with gs_restore to restore the database. The system allows users to select or even to sort the content to be imported.

Functions

gs_dump can create export files in four formats, which are specified by -F or --format=, as listed in Table 1.

Table 1 Formats of exported files

Format

Value of -F

Description

Suggestion

Corresponding Import Tool

Plain-text

p

A plain-text script file containing SQL statements and commands. The commands can be executed on gsql, a command line terminal, to recreate database objects and load table data.

You are advised to use plain-text exported files for small databases.

Before using gsql to restore database objects, you can use a text editor to edit the plain-text export file as required.

Custom

c

A binary file that allows the restoration of all or selected database objects from an exported file.

You are advised to use custom-format archive files for medium or large database.

You can use gs_restore to import database objects from a custom-format archive.

Directory

d

A directory containing directory files and the data files of tables and BLOB objects.

-

.tar

t

A tar-format archive that allows the restoration of all or selected database objects from an exported file. It cannot be further compressed and has an 8-GB limitation on the size of a single table.

-

NOTE: To reduce the size of an exported file, you can use gs_dump to compress it to a plain-text file or custom-format file. By default, a plain-text file is not compressed when generated. When a custom-format archive is generated, a medium level of compression is applied by default. Archived exported files cannot be compressed using gs_dump. When a plain-text file is exported in compressed mode, gsql fails to import data objects.

Precautions

Do not modify an exported file or its content. Otherwise, restoration may fail.

To ensure the data consistency and integrity, gs_dump acquires a share lock on a table to be dumped. If another transaction has acquired a share lock on the table, gs_dump waits until this lock is released and then locks the table for dumping. If the table cannot be locked within the specified time, the dump fails. You can customize the timeout duration to wait for lock release by specifying the --lock-wait-timeout parameter.

Syntax

gs_dump [OPTION]... [DBNAME]

NOTE: DBNAME does not follow a short or long option. It specifies the database to be connected. For example: Specify DBNAME without a -d option preceding it.

gs_dump -p port_number  postgres -f dump1.sql

or

export PGDATABASE=postgres 
 gs_dump -p port_number -f dump1.sql

Environment variable: PGDATABASE

Parameter Description

Common parameters

  • -f, --file=FILENAME

    Sends the output to the specified file or directory. If this parameter is omitted, the standard output is generated. If the output format is (-F c/-F d/-F t), the -f parameter must be specified. If the value of the -f parameter contains a directory, the current user must have the read and write permissions on the directory, and the directory cannot be an existing one.

  • -F, --format=c|d|t|p

    Selects the exported file format. The format can be:

    • p|plain: Generates a text SQL script file. This is the default value.

    • c|custom: Outputs a custom-format archive as a directory to be used as the input of gs_restore. This is the most flexible output format in which users can manually select it and reorder the archived items during restoration. An archive in this format is compressed by default.

    • d|directory: Creates a directory containing directory files and the data files of tables and BLOBs.

    • t|tar: Outputs a .tar archive as the input of gs_restore. The .tar format is compatible with the directory format. Extracting a .tar archive generates a valid directory-format archive. However, the .tar archive cannot be further compressed and has an 8-GB limitation on the size of a single table. The order of table data items cannot be changed during restoration.

      A .tar archive can be used as input of gsql.

  • -v, --verbose

    Specifies the verbose mode. If it is specified, gs_dump writes detailed object comments and the number of startups/stops to the dump file, and progress messages to standard error.

  • -V, --version

    Prints the gs_dump version and exits.

  • -Z, --compress=0-9

    Specifies the used compression level.

    Value range: 0-9

    • 0 indicates no compression.
    • 1 indicates that the compression ratio is the lowest and processing speed the fastest.
    • 9 indicates that the compression ratio is the highest and processing speed the slowest.

    For the custom-format archive, this option specifies the compression level of a single table data segment. By default, data is compressed at a medium level. The .tar archive formats do not support compression currently.

  • --lock-wait-timeout=TIMEOUT

    Do not keep waiting to obtain shared table locks since the beginning of the dump. Consider it as failed if you are unable to lock a table within the specified time. The timeout period can be specified in any of the formats accepted by SET statement_timeout.

  • -?, --help

    Displays help about gs_dump parameters and exits.

Dump parameters:

  • -a, --data-only

    Generates only the data, not the schema (data definition). Dump the table data, big objects, and sequence values.

  • -b, --blobs

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • -c, --clean

    Before writing the command of creating database objects into the backup file, writes the command of clearing (deleting) database objects to the backup files. (If no objects exist in the target database, gs_restore probably displays some error information.)

    This parameter is used only for the plain-text format. For the archive format, you can specify the option when using gs_restore.

  • -C, --create

    The backup file content starts with the commands of creating the database and connecting to the created database. (If the command script is executed in this mode, you can specify any database to run the command for creating a database. The data is restored to the created database instead of the specified database.)

    This parameter is used only for the plain-text format. For the archive format, you can specify the option when using gs_restore.

  • -E, --encoding=ENCODING

    Creates a dump file in the specified character set encoding. By default, the dump file is created in the database encoding. (Alternatively, you can set the environment variable PGCLIENTENCODING to the required dump encoding.)

  • -n, --schema=SCHEMA

    Dumps only schemas matching the schema names. This option contains the schema and all its contained objects. If this option is not specified, all non-system schemas in the target database will be dumped. Multiple schemas can be selected by specifying multiple -n options. The schema parameter is interpreted as a pattern according to the same rules used by the \d command of gsql. Therefore, multiple schemas can also be selected by writing wildcard characters in the pattern. When you use wildcard characters, quote the pattern to prevent the shell from expanding the wildcard characters.

    NOTE:

    • If -n is specified, gs_dump does not dump any other database objects which the selected schemas might depend upon. Therefore, there is no guarantee that the results of a specific-schema dump can be automatically restored to an empty database.
    • If -n is specified, the non-schema objects are not dumped.

    Multiple schemas can be dumped. Entering **-n **schemaname multiple times dumps multiple schemas.

    For example:

    gs_dump -h host_name -p port_number postgres -f backup/bkp_shl2.sql -n sch1 -n sch2
    

    In the preceding example, sch1 and sch2 are dumped.

  • -N, --exclude-schema=SCHEMA

    Does not dump any schemas matching the schemas pattern. The pattern is interpreted according to the same rules as for -n. -N can be specified multiple times to exclude schemas matching any of the specified patterns.

    When both -n and -N are specified, the schemas that match at least one -n option but no -N is dumped. If -N is specified and -n is not, the schemas matching -N are excluded from what is normally dumped.

    Dump allows you to exclude multiple schemas during dumping.

    Specify -N exclude schema name to exclude multiple schemas during dumping.

    For example:

    gs_dump -h host_name -p port_number postgres -f backup/bkp_shl2.sql -N sch1 -N sch2
    

    In the preceding example, sch1 and sch2 will be excluded during the dumping.

  • -o, --oids

    Dumps object identifiers (OIDs) as parts of the data in each table. Use this option if your application references the OID columns in some way. If the preceding situation does not occur, do not use this parameter.

  • -O, --no-owner

    Do not output commands to set ownership of objects to match the original database. By default, gs_dump issues the ALTER OWNER or SET SESSION AUTHORIZATION statement to set ownership of created database objects. These statements will fail when the script is running unless it is started by a system administrator (or the same user that owns all of the objects in the script). To make a script that can be stored by any user and give the user ownership of all objects, specify -O.

    This parameter is used only for the plain-text format. For the archive format, you can specify the option when using gs_restore.

  • -s, --schema-only

    Dumps only the object definition (schema) but not data.

  • -S, --sysadmin=NAME

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • -t, --table=TABLE

    Specifies a list of tables, views, sequences, or foreign tables to be dumped. You can use multiple -t parameters or wildcard characters to specify tables.

    When you use wildcard characters, quote patterns to prevent the shell from expanding the wildcard characters.

    The -n and -N options have no effect when -t is used, because tables selected by using -t will be dumped regardless of those options.

    NOTE:

    • The number of -t parameters must be less than or equal to 100.
    • If the number of -t parameters is greater than 100, you are advised to use the --include-table-file parameter to replace some -t parameters.
    • If -t is specified, gs_dump does not dump any other database objects which the selected tables might depend upon. Therefore, there is no guarantee that the results of a specific-table dump can be automatically restored to an empty database.
    • -t tablename only dumps visible tables in the default search path. -t '*.tablename' dumps tablename tables in all the schemas of the dumped database. -t schema.table dumps tables in a specific schema.
    • -t tablename does not export trigger information from a table.

    For example:

    gs_dump -h host_name -p port_number postgres -f backup/bkp_shl2.sql -t schema1.table1 -t schema2.table2
    

    In the preceding example, schema1.table1 and schema2.table2 are dumped.

  • --include-table-file=FILENAME

    Specifies the table file to be dumped.

  • -T, --exclude-table=TABLE

    Specifies a list of tables, views, sequences, or foreign tables not to be dumped. You can use multiple -T parameters or wildcard characters to specify tables.

    When -t and -T are input, the object will be stored in -t list not -T table object.

    For example:

    gs_dump -h host_name -p port_number postgres -f backup/bkp_shl2.sql -T table1 -T table2
    

    In the preceding example, table1 and table2 are excluded from the dumping.

  • --exclude-table-file=FILENAME

    Specifies the table files that do not need to be dumped.

    NOTE: Same as --include-table-file, the content format of this parameter is as follows: schema1.table1 schema2.table2 ……

  • -x, --no-privileges|--no-acl

    Prevents the dumping of access permissions (grant/revoke commands).

  • --binary-upgrade

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • --binary-upgrade-usermap=“USER1=USER2”

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • --column-inserts|--attribute-inserts

    Exports data by running the INSERT command with explicit column names {INSERT INTO table (column, …) VALUES …}. This will cause a slow restoration. However, since this option generates an independent command for each row, an error in reloading a row causes only the loss of the row rather than the entire table content.

  • --disable-dollar-quoting

    Disables the use of dollar sign ($) for function bodies, and forces them to be quoted using the SQL standard string syntax.

  • --disable-triggers

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • --exclude-table-data=TABLE

    Does not dump data that matches any of table patterns. The pattern is interpreted according to the same rules as for -t.

    --exclude-table-data can be entered more than once to exclude tables matching any of several patterns. When you need the specified table definition rather than data in the table, this option is helpful.

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

  • --inserts

    Dumps data by the INSERT statement (rather than COPY). This will cause a slow restoration.

    However, since this option generates an independent command for each row, an error in reloading a row causes only the loss of the row rather than the entire table content. The restoration may fail if you rearrange the column order. The --column-inserts option is unaffected against column order changes, though even slower.

  • --no-security-labels

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • --no-tablespaces

    Does not issue commands to select tablespaces. All the objects will be created during restoration, no matter which tablespace is selected when using this option.

    This parameter is used only for the plain-text format. For the archive format, you can specify the option when using gs_restore.

  • --no-unlogged-table-data

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • --non-lock-table

    Specifies a reserved port for function expansion. This parameter is not recommended.

  • --include-alter-table

    Dumps deleted columns of tables. This option records deleted columns.

  • --quote-all-identifiers

    Forcibly quotes all identifiers. This parameter is useful when you dump a database for migration to a later version, in which additional keywords may be introduced.

  • --section=SECTION

    Specifies dumped name sections (pre-data, data, or post-data).

  • --serializable-deferrable

    Uses a serializable transaction for the dump to ensure that the used snapshot is consistent with later database status. Perform this operation at a time point in the transaction flow, at which everything is normal. This ensures successful transaction and avoids serialization failures of other transactions, which requires serialization again.

    This option has no benefits for disaster recovery. During the upgrade of the original database, loading a database copy as a report or loading other shared read-only dump is helpful. If the option does not exist, dump reveals a status which is different from the submitted sequence status of any transaction.

    This option will make no difference if there are no active read-write transactions when gs_dump is started. If the read-write transactions are in active status, the dump start time will be delayed for an uncertain period.

  • --use-set-session-authorization

    Specifies that the standard SQL SET SESSION AUTHORIZATION command rather than ALTER OWNER is returned to ensure the object ownership. This makes dumping more standard. However, if a dump file contains objects that have historical problems, restoration may fail. A dump using SET SESSION AUTHORIZATION requires the system administrator permissions, whereas ALTER OWNER requires lower permissions.

  • --with-encryption=AES128

    Specifies that dumping data needs to be encrypted using AES128.

  • --with-key=KEY

    Specifies that the key length of AES128 must be 16 bytes.

  • --include-depend-objs

    Includes information about the objects that depend on the specified object in the backup result. This parameter takes effect only if the -t or --include-table-file parameter is specified.

  • --exclude-self

    Excludes information about the specified object from the backup result. This parameter takes effect only if the -t or --include-table-file parameter is specified.

  • --dont-overwrite-file

    The existing files in plain-text, .tar, and custom formats will be overwritten. This option is not used for the directory format.

    For example:

    Assume that the backup.sql file exists in the current directory. If you specify -f backup.sql in the input command, and the backup.sql file is generated in the current directory, the original file will be overwritten.

    If the backup file already exists and --dont-overwrite-file is specified, an error will be reported with the message that the dump file exists.

    gs_dump -p port_number postgres -f backup.sql -F plain --dont-overwrite-file
    

NOTE:

  • The -s/--schema-only and -a/--data-only parameters do not coexist.
  • The -c/--clean and -a/--data-only parameters do not coexist.
  • --inserts/--column-inserts and -o/--oids do not coexist, because OIDS cannot be set using the INSERT statement.
  • --role must be used in conjunction with --rolepassword.
  • --binary-upgrade-usermap must be used in conjunction with --binary-upgrade.
  • --include-depend-objs or --exclude-self takes effect only when -t or --include-table-file is specified.
  • --exclude-self must be used in conjunction with --include-depend-objs.

Connection parameters:

  • -h, --host=HOSTNAME

    Specifies the host name. If the value begins with a slash (/), it is used as the directory for the UNIX domain socket. The default value is taken from the PGHOST environment variable (if available). Otherwise, a Unix domain socket connection is attempted.

    This parameter is used only for defining names of the hosts outside openGauss. The names of the hosts inside openGauss must be 127.0.0.1.

    Example: host name

    Environment variable: PGHOST

  • -p, --port=PORT

    Specifies the host port number. If the thread pool function is enabled, you are advised to use pooler port, that is, the host port number plus 1.

    Environment variable: PGPORT

  • -U, --username=NAME

    Specifies the username of the host to be connected.

    If the username of the host to be connected is not specified, the system administrator is used by default.

    Environment variable: PGUSER

  • -w, --no-password

    Never issues a password prompt. The connection attempt fails if the host requires password verification and the password is not provided in other ways. This parameter is useful in batch jobs and scripts in which no user password is required.

  • -W, --password=PASSWORD

    Specifies the user password for connection. If the host uses the trust authentication policy, the administrator does not need to enter the -W option. If the -W option is not provided and you are not a system administrator, the Dump Restore tool will ask you to enter a password.

  • --role=ROLENAME

    Specifies a role name to be used for creating the dump. If this option is selected, the SET ROLE command will be issued after the database is connected to gs_dump. It is useful when the authenticated user (specified by -U) lacks the permissions required by gs_dump. It allows the user to switch to a role with the required permissions. Some installations have a policy against logging in directly as a super administrator. This option allows dumping data without violating the policy.

  • --rolepassword=ROLEPASSWORD

    Specifies the password for a role.

Notice

If any local additions need to be added to the template1 database in openGauss, restore the output of gs_dump into an empty database with caution. Otherwise, you are likely to obtain errors due to duplicate definitions of the added objects. To create an empty database without any local additions, copy data from template0 rather than template1. Example:

CREATE DATABASE foo WITH TEMPLATE template0;

The .tar file size must be smaller than 8 GB. (This is the .tar file format limitations.) The total size of a .tar archive and any of the other output formats are not limited, except possibly by the OS.

The dump file generated by gs_dump does not contain the statistics used by the optimizer to make execution plans. Therefore, you are advised to run ANALYZE after restoring from a dump file to ensure optimal performance. The dump file does not contain any ALTER DATABASE … SET commands. These settings are dumped by gs_dumpall, along with database users and other installation settings.

Examples

Use gs_dump to dump a database as a SQL text file or a file in other formats.

In the following examples, Bigdata@123 indicates the password for the database user. backup/MPPDB_backup.sql indicates an exported file where backup indicates the relative path of the current directory. 37300 indicates the port number of the database server. postgres indicates the name of the database to be accessed.

NOTE: Before exporting files, ensure that the directory exists and you have the read and write permissions on the directory.

Example 1: Use gs_dump to export the full information of the postgres database. The exported MPPDB_backup.sql file is in plain-text format.

gs_dump -U omm -W Bigdata@123 -f backup/MPPDB_backup.sql -p 37300 postgres -F p
gs_dump[port='37300'][postgres][2018-06-27 09:49:17]: The total objects number is 356.
gs_dump[port='37300'][postgres][2018-06-27 09:49:17]: [100.00%] 356 objects have been dumped.
gs_dump[port='37300'][postgres][2018-06-27 09:49:17]: dump database postgres successfully
gs_dump[port='37300'][postgres][2018-06-27 09:49:17]: total time: 1274  ms

Use gsql to import data from the exported plain-text file.

Example 2: Use gs_dump to export the full information of the postgres database. The exported MPPDB_backup.tar file is in .tar format.

gs_dump -U omm -W Bigdata@123 -f backup/MPPDB_backup.tar -p 37300 postgres -F t
gs_dump[port='37300'][postgres][2018-06-27 10:02:24]: The total objects number is 1369.
gs_dump[port='37300'][postgres][2018-06-27 10:02:53]: [100.00%] 1369 objects have been dumped.
gs_dump[port='37300'][postgres][2018-06-27 10:02:53]: dump database postgres successfully
gs_dump[port='37300'][postgres][2018-06-27 10:02:53]: total time: 50086  ms

Example 3: Use gs_dump to export the full information of the postgres database. The exported MPPDB_backup.dmp file is in custom format.

gs_dump -U omm -W Bigdata@123 -f backup/MPPDB_backup.dmp -p 37300 postgres -F c
gs_dump[port='37300'][postgres][2018-06-27 10:05:40]: The total objects number is 1369.
gs_dump[port='37300'][postgres][2018-06-27 10:06:03]: [100.00%] 1369 objects have been dumped.
gs_dump[port='37300'][postgres][2018-06-27 10:06:03]: dump database postgres successfully
gs_dump[port='37300'][postgres][2018-06-27 10:06:03]: total time: 36620  ms

Example 4: Use gs_dump to export the full information of the postgres database. The exported MPPDB_backup file is in directory format.

gs_dump -U omm -W Bigdata@123 -f backup/MPPDB_backup -p 37300  postgres -F d
gs_dump[port='37300'][postgres][2018-06-27 10:16:04]: The total objects number is 1369.
gs_dump[port='37300'][postgres][2018-06-27 10:16:23]: [100.00%] 1369 objects have been dumped.
gs_dump[port='37300'][postgres][2018-06-27 10:16:23]: dump database postgres successfully
gs_dump[port='37300'][postgres][2018-06-27 10:16:23]: total time: 33977  ms 

Example 5: Use gs_dump to export the information of the postgres database, excluding the information of the table specified in the /home/MPPDB_temp.sql file. The exported MPPDB_backup.sql file is in plain-text format.

gs_dump -U omm -W Bigdata@123 -p 37300 postgres --exclude-table-file=/home/MPPDB_temp.sql -f backup/MPPDB_backup.sql
gs_dump[port='37300'][postgres][2018-06-27 10:37:01]: The total objects number is 1367.
gs_dump[port='37300'][postgres][2018-06-27 10:37:22]: [100.00%] 1367 objects have been dumped.
gs_dump[port='37300'][postgres][2018-06-27 10:37:22]: dump database postgres successfully
gs_dump[port='37300'][postgres][2018-06-27 10:37:22]: total time: 37017  ms

Example 6: Use gs_dump to export only the information about the views that depend on the testtable table. Create another testtable table, and then restore the views that depend on it.

  • Back up only the views that depend on the testtable table.

    gs_dump -s -p 37300 postgres -t PUBLIC.testtable --include-depend-objs --exclude-self -f backup/MPPDB_backup.sql -F p
    gs_dump[port='37300'][postgres][2018-06-15 14:12:54]: The total objects number is 331.
    gs_dump[port='37300'][postgres][2018-06-15 14:12:54]: [100.00%] 331 objects have been dumped.
    gs_dump[port='37300'][postgres][2018-06-15 14:12:54]: dump database postgres successfully
    gs_dump[port='37300'][postgres][2018-06-15 14:12:54]: total time: 327  ms
    
  • Change the name of the testtable table.

    gsql -p 37300 postgres -r -c "ALTER TABLE PUBLIC.testtable RENAME TO testtable_bak;"
    
  • Create another testtable table.

    CREATE TABLE PUBLIC.testtable(a int, b int, c int);
    
  • Restore the views for the new testtable table.

    gsql -p 37300 postgres -r -f backup/MPPDB_backup.sql
    

Helpful Links

gs_dumpall and gs_restore

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