Friday, June 12, 2009

postgresql backup information


How To Backup and Restore PostgreSQL Database Using pg_dump and psql
pg_dump is an effective tool to backup postgres database. It creates a *.sql file with CREATE TABLE, ALTER TABLE, and COPY SQL statements of source database. To restore these dumps psql command is enough.

Using pg_dump, you can backup a local database and restore it on a remote database at the same time, using a single command. In this article, let us review several practical examples on how to use pg_dump to backup and restore.

For the impatient, here is the quick snippet of how backup and restore postgres database using pg_dump and psql:

Backup: $ pg_dump -U {user-name} {source_db} -f {dumpfilename.sql}

Restore: $ psql -U {user-name} -d {desintation_db}-f {dumpfilename.sql}

How To Backup Postgres Database
1. Backup a single postgres database

This example will backup erp database that belongs to user geekstuff, to the file mydb.sql

$ pg_dump -U geekstuff erp -f mydb.sql

It prompts for password, after authentication mydb.sql got created with create table, alter table and copy commands for all the tables in the erp database. Following is a partial output of mydb.sql showing the dump information of employee_details table.

-- Name: employee_details; Type: TABLE; Schema: public; Owner: geekstuff; Tablespace:

CREATE TABLE employee_details (
employee_name character varying(100),
emp_id integer NOT NULL,
designation character varying(50),
comments text

ALTER TABLE public.employee_details OWNER TO geekstuff;

-- Data for Name: employee_details; Type: TABLE DATA; Schema: public; Owner: geekstuff
COPY employee_details (employee_name, emp_id, designation, comments) FROM stdin;
geekstuff 1001 trainer
ramesh 1002 author
sathiya 1003 reader
-- Name: employee_details_pkey; Type: CONSTRAINT; Schema: public; Owner: geekstuff; Tablespace:
ALTER TABLE ONLY employee_details

ADD CONSTRAINT employee_details_pkey PRIMARY KEY (emp_id);

2. Backup all postgres databases

To backup all databases, list out all the available databases as shown below.
Login as postgres / psql user:

$ su postgres

List the databases:

$ psql -l

List of databases
Name | Owner | Encoding
article | sathiya | UTF8
backup | postgres | UTF8
erp | geekstuff | UTF8
geeker | sathiya | UTF8

Backup all postgres databases using pg_dumpall:

You can backup all the databases using pg_dumpall command.

$ pg_dumpall > all.sql

Verify the backup:

Verify whether all the databases are backed up,

$ grep "^[\]connect” all.sql
\connect article
\connect backup
\connect erp
\connect geeker

3. Backup a specific postgres table

$ pg_dump --table products -U geekstuff article -f onlytable.sql

To backup a specific table, use the –table TABLENAME option in the pg_dump command. If there are same table names in different schema then use the –schema SCHEMANAME option.
How To Restore Postgres Database
1. Restore a postgres database

$ psql -U erp -d erp_devel -f mydb.sql

This restores the dumped database to the erp_devel database.
Restore error messages

While restoring, there may be following errors and warning, which can be ignored.

psql:mydb.sql:13: ERROR: must be owner of schema public
psql:mydb.sql:34: ERROR: must be member of role "geekstuff"
psql:mydb.sql:59: WARNING: no privileges could be revoked
psql:mydb.sql:60: WARNING: no privileges could be revoked
psql:mydb.sql:61: WARNING: no privileges were granted
psql:mydb.sql:62: WARNING: no privileges were granted

2. Backup a local postgres database and restore to remote server using single command:

$ pg_dump dbname | psql -h hostname dbname

The above dumps the local database, and extracts it at the given hostname.
3. Restore all the postgres databases

$ su postgres
$ psql -f alldb.sql

4. Restore a single postgres table

The following psql command installs the patientinfo table in the database pacs.

$ psql -f patientinfo.sql pacs