lt_restore

lt_restore
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Description

lt_restore is a utility for restoring a LightDB database from an archive created by lt_dump in one of the non-plain-text formats. It will issue the commands necessary to reconstruct the database to the state it was in at the time it was saved. The archive files also allow lt_restore to be selective about what is restored, or even to reorder the items prior to being restored. The archive files are designed to be portable across architectures.

lt_restore can operate in two modes. If a database name is specified, lt_restore connects to that database and restores archive contents directly into the database. Otherwise, a script containing the SQL commands necessary to rebuild the database is created and written to a file or standard output. This script output is equivalent to the plain text output format of lt_dump. Some of the options controlling the output are therefore analogous to lt_dump options.

Obviously, lt_restore cannot restore information that is not present in the archive file. For instance, if the archive was made using the “dump data as INSERT commands” option, lt_restore will not be able to load the data using COPY statements.

Options

lt_restore accepts the following command line arguments.

filename

Specifies the location of the archive file (or directory, for a directory-format archive) to be restored. If not specified, the standard input is used.

-a --data-only

Restore only the data, not the schema (data definitions). Table data, large objects, and sequence values are restored, if present in the archive.

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

-c --clean

Clean (drop) database objects before recreating them. (Unless --if-exists is used, this might generate some harmless error messages, if any objects were not present in the destination database.)

-K --recreate-schema

Output commands to directly drop schema(use cascade mode) prior to outputting the commands for creating them, more faster then normal mode. (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 ignored when emitting an archive (non-text) output file. For the archive formats, you can specify the option when you call lt_restore.

-C --create

Create the database before restoring into it. If --clean is also specified, drop and recreate the target database before connecting to it.

With --create, lt_restore also restores the database's comment if any, and any configuration variable settings that are specific to this database, that is, any ALTER DATABASE ... SET ... and ALTER ROLE ... IN DATABASE ... SET ... commands that mention this database. Access privileges for the database itself are also restored, unless --no-acl is specified.

When this option is used, the database named with -d is used only to issue the initial DROP DATABASE and CREATE DATABASE commands. All data is restored into the database name that appears in the archive.

-d dbname --dbname=dbname

Connect to database dbname and restore directly into the database. The dbname can be a connection string. If so, connection string parameters will override any conflicting command line options.

-e --exit-on-error

Exit if an error is encountered while sending SQL commands to the database. The default is to continue and to display a count of errors at the end of the restoration.

-f filename --file=filename

Specify output file for generated script, or for the listing when used with -l. Use - for stdout.

-F format --format=format

Specify format of the archive. It is not necessary to specify the format, since lt_restore will determine the format automatically. If specified, it can be one of the following:

c custom: The archive is in the custom format of lt_dump.
d directory: The archive is a directory archive.
t tar: The archive is a tar archive.

-I index --index=index

Restore definition of named index only. Multiple indexes may be specified with multiple -I switches.

-j number-of-jobs --jobs=number-of-jobs

Run the most time-consuming steps of lt_restore — those that load data, create indexes, or create constraints — concurrently, using up to number-of-jobs concurrent sessions. This option can dramatically reduce the time to restore a large database to a server running on a multiprocessor machine. This option is ignored when emitting a script rather than connecting directly to a database server.

Each job is one process or one thread, depending on the operating system, and uses a separate connection to the server.

The optimal value for this option depends on the hardware setup of the server, of the client, and of the network. Factors include the number of CPU cores and the disk setup. A good place to start is the number of CPU cores on the server, but values larger than that can also lead to faster restore times in many cases. Of course, values that are too high will lead to decreased performance because of thrashing.

Only the custom and directory archive formats are supported with this option. The input must be a regular file or directory (not, for example, a pipe or standard input). Also, multiple jobs cannot be used together with the option --single-transaction.

-l --list

List the table of contents of the archive. The output of this operation can be used as input to the -L option. Note that if filtering switches such as -n or -t are used with -l, they will restrict the items listed.

-L list-file --use-list=list-file

Restore only those archive elements that are listed in list-file, and restore them in the order they appear in the file. Note that if filtering switches such as -n or -t are used with -L, they will further restrict the items restored.

list-file is normally created by editing the output of a previous -l operation. Lines can be moved or removed, and can also be commented out by placing a semicolon (;) at the start of the line. See below for examples.

-n schema --schema=schema

Restore only objects that are in the named schema. Multiple schemas may be specified with multiple -n switches. This can be combined with the -t option to restore just a specific table.

-N schema --exclude-schema=schema

Do not restore objects that are in the named schema. Multiple schemas to be excluded may be specified with multiple -N switches.

When both -n and -N are given for the same schema name, the -N switch wins and the schema is excluded.

-O --no-owner

Do not output commands to set ownership of objects to match the original database. By default, lt_restore issues ALTER OWNER or SET SESSION AUTHORIZATION statements to set ownership of created schema elements. These statements will fail unless the initial connection to the database is made by a superuser (or the same user that owns all of the objects in the script). With -O, any user name can be used for the initial connection, and this user will own all the created objects.

-P function-name(argtype [, ...]) --function=function-name(argtype [, ...])

Restore the named function only. Be careful to spell the function name and arguments exactly as they appear in the dump file's table of contents. Multiple functions may be specified with multiple -P switches.

-R --no-reconnect

This option is obsolete but still accepted for backwards compatibility.

-s --schema-only

Restore only the schema (data definitions), not data, to the extent that schema entries are present in the archive.

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.)

-S username --superuser=username

Specify the superuser user name to use when disabling triggers. This is relevant only if --disable-triggers is used.

-t table --table=table

Restore definition and/or data of only the named table. For this purpose, “table” includes views, materialized views, sequences, and foreign tables. Multiple tables can be selected by writing multiple -t switches. This option can be combined with the -n option to specify table(s) in a particular schema.

Note

When -t is specified, lt_restore makes no attempt to restore any other database objects that the selected table(s) might depend upon. Therefore, there is no guarantee that a specific-table restore into a clean database will succeed.

Note

This flag does not behave identically to the -t flag of lt_dump. There is not currently any provision for wild-card matching in lt_restore, nor can you include a schema name within its -t. And, while lt_dump's -t flag will also dump subsidiary objects (such as indexes) of the selected table(s), lt_restore's -t flag does not include such subsidiary objects.

Note

In versions prior to LightDB 9.6, this flag matched only tables, not any other type of relation.

-T trigger --trigger=trigger

Restore named trigger only. Multiple triggers may be specified with multiple -T switches.

-v --verbose

Specifies verbose mode.

-V --version

Print the lt_restore version and exit.

-x --no-privileges --no-acl

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

-1 --single-transaction

Execute the restore as a single transaction (that is, wrap the emitted commands in BEGIN/COMMIT). This ensures that either all the commands complete successfully, or no changes are applied. This option implies --exit-on-error.

--disable-triggers

This option is relevant only when performing a data-only restore. It instructs lt_restore to execute commands to temporarily disable triggers on the target tables while the data is restored. Use this if you have referential integrity checks or other triggers on the tables that you do not want to invoke during data restore.

Presently, the commands emitted for --disable-triggers must be done as superuser. So you should also specify a superuser name with -S or, preferably, run lt_restore as a LightDB superuser.

--enable-row-security

This option is relevant only when restoring the contents of a table which has row security. By default, lt_restore will set row_security to off, to ensure that all data is restored in to the table. If the user does not have sufficient privileges to bypass row security, then an error is thrown. This parameter instructs lt_restore to set row_security to on instead, allowing the user to attempt to restore the contents of the table with row security enabled. This might still fail if the user does not have the right to insert the rows from the dump into the table.

Note that this option currently also requires the dump be in INSERT format, as COPY FROM does not support row security.

--if-exists

Use conditional commands (i.e., add an IF EXISTS clause) to drop database objects. This option is not valid unless --clean is also specified.

--no-comments

Do not output commands to restore comments, even if the archive contains them.

--no-data-for-failed-tables

By default, table data is restored even if the creation command for the table failed (e.g., because it already exists). With this option, data for such a table is skipped. This behavior is useful if the target database already contains the desired table contents. For example, auxiliary tables for LightDB extensions such as PostGIS might already be loaded in the target database; specifying this option prevents duplicate or obsolete data from being loaded into them.

This option is effective only when restoring directly into a database, not when producing SQL script output.

--no-publications

Do not output commands to restore publications, even if the archive contains them.

--no-security-labels

Do not output commands to restore security labels, even if the archive contains them.

--no-subscriptions

Do not output commands to restore subscriptions, even if the archive contains them.

--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.

--section=sectionname

Only restore 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 restore all sections.

The data section contains actual table data as well as large-object definitions. Post-data items consist of definitions of indexes, triggers, rules and constraints other than validated check constraints. Pre-data items consist of all other data definition items.

--strict-names

Require that each schema (-n/--schema) and table (-t/--table) qualifier match at least one schema/table in the backup file.

--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.

-? --help

Show help about lt_restore command line arguments, and exit.

lt_restore also accepts the following command line arguments for connection parameters:

-h host --host=host

Specifies the host name of the machine on which the server is running. If the value begins with a slash, it is used as the directory for the Unix domain socket. The default is taken from the LTHOST 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 LTPORT 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 lt_restore to prompt for a password before connecting to a database.

This option is never essential, since lt_restore will automatically prompt for a password if the server demands password authentication. However, lt_restore 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 perform the restore. This option causes lt_restore 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 lt_restore, 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 restores to be performed without violating the policy.

Environment

LTHOST LTOPTIONS LTPORT LTUSER: Default connection parameters
LT_COLOR: Specifies whether to use color in diagnostic messages. Possible values are always, auto and never.

This utility, like most other LightDB utilities, also uses the environment variables supported by libpq (see Section 32.14). However, it does not read LTDATABASE when a database name is not supplied.

Diagnostics

When a direct database connection is specified using the -d option, lt_restore internally executes SQL statements. If you have problems running lt_restore, make sure you are able to select information from the database using, for example, ltsql. Also, any default connection settings and environment variables used by the libpq front-end library will apply.

Notes

If your installation has any local additions to the template1 database, be careful to load the output of lt_restore 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;

The limitations of lt_restore are detailed below.

When restoring data to a pre-existing table and the option --disable-triggers is used, lt_restore emits commands to disable triggers on user tables before inserting the data, then emits 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.
lt_restore cannot restore large objects selectively; for instance, only those for a specific table. If an archive contains large objects, then all large objects will be restored, or none of them if they are excluded via -L, -t, or other options.

See also the lt_dump documentation for details on limitations of lt_dump.

Once restored, it is wise to run ANALYZE on each restored table so the optimizer has useful statistics; see Section 22.1.3 and Section 22.1.6 for more information.

Examples

Assume we have dumped a database called mydb into a custom-format dump file:

$ lt_dump -Fc mydb > db.dump

To drop the database and recreate it from the dump:

$ dropdb mydb
$ lt_restore -C -d postgres db.dump

The database named in the -d switch can be any database existing in the cluster; lt_restore only uses it to issue the CREATE DATABASE command for mydb. With -C, data is always restored into the database name that appears in the dump file.

To restore the dump into a new database called newdb:

$ createdb -T template0 newdb
$ lt_restore -d newdb db.dump

Notice we don't use -C, and instead connect directly to the database to be restored into. Also note that we clone the new database from template0 not template1, to ensure it is initially empty.

To reorder database items, it is first necessary to dump the table of contents of the archive:

$ lt_restore -l db.dump > db.list

The listing file consists of a header and one line for each item, e.g.:

;
; Archive created at Mon Sep 14 13:55:39 2009
;     dbname: DBDEMOS
;     TOC Entries: 81
;     Compression: 9
;     Dump Version: 1.10-0
;     Format: CUSTOM
;     Integer: 4 bytes
;     Offset: 8 bytes
;     Dumped from database version: 8.3.5
;     Dumped by lt_dump version: 8.3.8
;
;
; Selected TOC Entries:
;
3; 2615 2200 SCHEMA - public pasha
1861; 0 0 COMMENT - SCHEMA public pasha
1862; 0 0 ACL - public pasha
317; 1247 17715 TYPE public composite pasha
319; 1247 25899 DOMAIN public domain0 pasha

Semicolons start a comment, and the numbers at the start of lines refer to the internal archive ID assigned to each item.

Lines in the file can be commented out, deleted, and reordered. For example:

10; 145433 TABLE map_resolutions postgres
;2; 145344 TABLE species postgres
;4; 145359 TABLE nt_header postgres
6; 145402 TABLE species_records postgres
;8; 145416 TABLE ss_old postgres

could be used as input to lt_restore and would only restore items 10 and 6, in that order:

$ lt_restore -L db.list db.dump

lt_restore

Synopsis

Description

Options

Note

Note

Note

Environment

Diagnostics

Notes

Examples

See Also