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118 lines
3.1 KiB
Plaintext
118 lines
3.1 KiB
Plaintext
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How to use pg_dumplo?
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=====================
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(c) 2000, Pavel Jan<61>k 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 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 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 has an oid
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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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Isn't it nice :-) Yes, it is, but we are on the half of our way. We should
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also be able to recreate the contents of the table lo and the Large Object
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database when something went wrong. It is very easy, we will demonstrate
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this via dropping the database and recreating it from scratch with
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pg_dumplo:
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SnowwWite:$ dropdb test
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DROP DATABASE
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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 again. We should also
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create the table `lo' again:
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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=# \q
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SnowWhite:$
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Now the database with the table `lo' is created again, but we do not have
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any information stored in it. But have the dump of complete Large Object
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database, so we can recreate the contents of the whole database from the
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directory /tmp/dump:
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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.
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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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