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I have Postgresql versions 8.4 and 9.1 installed. For any given Postgresql command, how do I specify a specific version of the command to run? (e.g., psql, pg_dump, pg_ctlcluster, pg_restore, ...)

My question is motivated by wanting to do a pg_dump in preparation for an upgrade from 8.4 to 9.1, and I want to know which pg_dump version I am running.

I'm running on Ubuntu 10.04 Natty.

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The question is probably better suited for dba.SE. –  Erwin Brandstetter Jul 14 '12 at 17:56

1 Answer 1

up vote 5 down vote accepted

You are on Ubuntu and obviously have Martin Pitt's pg_wrapper installed (judging from pg_ctlcluster) that is provided by the package postgresql-common and comes with the standard Debian packages. I use the same on Debian.

On a Linux system, run which in the shell to see which executable is actually picked:

postgres@db:~$ which pg_dump
/usr/bin/pg_dump
postgres@db:~$ ls -l /usr/bin/pg_dump
lrwxrwxrwx 1 root root 37  4. Jun 18:57 /usr/bin/pg_dump -> ../share/postgresql-common/pg_wrapper

pg_dump is actually a symlink to pg_wrapper, which dynamically picks the appropriate version of the client program for the db cluster you run pg_dump with. I quote the man page of pg_wrapper:

This program is run only as a link to names which correspond to PostgreSQL programs in /usr/lib/postgresql/version/bin. It determines the configured cluster and database for the user and calls the appropriate version of the desired program to connect to that cluster and database, supplying any specified options to that command.

   The target cluster is selected by the following means, in descending order of precedence:
   1.  explicit specification with the --cluster option
   2.  explicit specification with the PGCLUSTER environment variable
   3.  matching entry in ~/.postgresqlrc (see postgresqlrc(5)), if that file exists
   4.  matching entry in /etc/postgresql-common/user_clusters (see user_clusters(5)), if that file exists
   5.  If only one local cluster exists, that one will be selected.
   6.  If several local clusters exist, the one listening on the default port 5432 will be selected.

   If none of these rules match, pg_wrapper aborts with an error.

IOW, the right version should be picked automagically - unless you screwed up your installation somehow. You can always add the option --cluster to be specific.

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Perfect, thanks @Erwin_Brandstetter! –  Rob Bednark Jul 14 '12 at 18:24
    
Just a note: this doesn't help with remote connections. I have 8.3 and 9.1 client tools installed and it defaults to 8.3 for some reason. I have to manually select the path in /usr/lib to use the correct version. I would've thought that the newest one would be used by default, but seems not. –  Sami Kuhmonen Mar 28 at 10:59
    
You do not need the newest one, but the one matching your database. For some purposes the new version of pg_dump may be the better option, though. –  Erwin Brandstetter Mar 28 at 15:22
    
Can you please clarify what exactly needs to go in the ~/.postgreslqrc file? My client output --> psql (8.4.21, server 9.1.13) WARNING: psql version 8.4, server version 9.1. Some psql features might not work. –  Croydon Dias May 14 at 6:36
    
That does not seem to work for me. I created a dump on a server with 9.1, and when I tried to restore on another server with 9.1 and 8.4, it tells me it cannot recognize the file format. Also, there is no --cluster command line option. –  Alexis Wilke Jun 10 at 5:31

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