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149 lines
4.0 KiB
Plaintext
$Header: /cvsroot/pgsql/contrib/pg_dumplo/Attic/README.pg_dumplo,v 1.2 2000/11/22 00:00:55 tgl Exp $
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pg_dumplo - PostgreSQL large object dumper
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==========================================
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By Karel Zak <zakkr@zf.jcu.cz>
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Compilation:
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===========
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* run master ./configure in the PG source top directory
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* gmake all
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* gmake install
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THANKS:
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======
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<??? I lost his e-mail ???>
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* option '--all' and pg_class usage
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Pavel Janík ml. <Pavel.Janik@linux.cz>
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* HOWTO (the rest of this file)
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How to use pg_dumplo?
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=====================
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(c) 2000, Pavel Janík ml. <Pavel.Janik@linux.cz>
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Q: How do you use pg_dumplo?
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============================
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A: This is a small demo of backing up the database table with Large Objects:
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We will create a demo database and a small and useless table `lo' inside
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it:
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SnowWhite:$ createdb test
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CREATE DATABASE
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Ok, our database with the name 'test' is created. Now we should create demo
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table which will contain only one column with the name 'id' which will hold
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the OID number of a Large Object:
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SnowWhite:$ psql test
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Welcome to psql, the PostgreSQL interactive terminal.
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Type: \copyright for distribution terms
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\h for help with SQL commands
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\? for help on internal slash commands
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\g or terminate with semicolon to execute query
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\q to quit
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test=# CREATE TABLE lo (id oid);
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CREATE
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test=# \lo_import /etc/aliases
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lo_import 19338
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test=# INSERT INTO lo VALUES (19338);
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INSERT 19352 1
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test=# select * from lo;
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id
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-------
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19338
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(1 row)
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test=# \q
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In the above example you can see that we have also imported one "Large
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Object" - the file /etc/aliases. It has an oid of 19338 so we have inserted
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this oid number to the database table lo to the column id. The final SELECT
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shows that we have one record in the table.
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Now we can demonstrate the work of pg_dumplo. We will create a dump directory
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which will contain the whole dump of large objects (/tmp/dump):
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mkdir -p /tmp/dump
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Now we can dump all large objects from the database `test' which have OIDs
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stored in the column `id' in the table `lo':
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SnowWhite:$ pg_dumplo -s /tmp/dump -d test -l lo.id
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pg_dumplo: dump lo.id (1 large obj)
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Voila, we have the dump of all Large Objects in our directory:
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SnowWhite:$ tree /tmp/dump/
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/tmp/dump/
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`-- test
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|-- lo
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| `-- id
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| `-- 19338
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`-- lo_dump.index
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3 directories, 2 files
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SnowWhite:$
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In practice, we'd probably use
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SnowWhite:$ pg_dumplo -s /tmp/dump -d test -e
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to export all large objects that are referenced by any OID-type column
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in the database. Calling out specific column(s) with -l is only needed
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for a selective dump.
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For routine backup purposes, the dump directory could now be converted into
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an archive file with tar and stored on tape. Notice that a single dump
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directory can hold the dump of multiple databases.
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Now, how can we recreate the contents of the table lo and the Large Object
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database when something went wrong? To do this, we expect that pg_dump is
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also used to store the definition and contents of the regular tables in
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the database.
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SnowWhite:$ pg_dump test >test.backup
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Now, if we lose the database:
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SnowWhite:$ dropdb test
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DROP DATABASE
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we can recreate it and reload the regular tables from the dump file:
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SnowWhite:$ createdb test
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CREATE DATABASE
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SnowWhite:$ psql test <test.backup
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But at this point our database has no large objects in it. What's more,
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the large-object-referencing columns contain the OIDs of the old large
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objects, which will not be the OIDs they'll have when reloaded. Never
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fear: pg_dumplo will fix the large object references at the same time
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it reloads the large objects. We reload the LO data from the dump
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directory like this:
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SnowWhite:$ pg_dumplo -s /tmp/dump -d test -i
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19338 lo id test/lo/id/19338
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SnowWhite:$
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And this is everything. The contents of table lo will be automatically
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updated to refer to the new large object OIDs.
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Summary: In this small example we have shown that pg_dumplo can be used to
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completely dump the database's Large Objects very easily.
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For more information see the help ( pg_dumplo -h ).
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