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