Date: Sun, 26 Aug 2007 17:35:15 -0400
From: Jean-David Beyer <jeandavid8@verizon.net>
Subject: Block size with pg_dump?
To: pgsql-sql@postgresql.org
Message-id: <46D1F213.4010107@verizon.net>
Organization: Institute for Regimented Whimsey
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When I make a backup of a database, I put the output file directly on
magnetic tape; i.e., my command looks like this:

pg_dump --file=/dev/st0 ....

This way I do not have to worry if the total backup exceeds the size of a
file system, and it saves me the trouble of copying it to the tape as a
separate step. My current tapes will hold 20 GBytes raw or 40GBytes if I
enable hardware compression (assuming 2:1 compression happens). Now it says
in the documentation that if I use format c it will compress the data in
software, so I doubt the hardware compression will do much.

I do not know what blocksize pg_dump uses, or if it insists on a particular
blocksize on input.

Now my tape drive will work with any blocksize, but prefers 65536-byte
blocks. I do not see any options for this in pg_dump, but I could pipe the
output of pg_dump through dd I suppose to make any blocksize I want.

On the way back, likewise I could pipe the tape through dd before giving it
to pg_restore.

Does pg_dump care what blocksize it gets? If so, what is it?

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  .~.  Jean-David Beyer          Registered Linux User 85642.
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