Compressing Oracle exports on the fly

Here is how to create compressed Oracle export files on the fly.

Here is how to create compressed Oracle export files on the fly even though the export utility does not support writing to the Unix standard output stream. It is been tested on versions 7.3 though 8.1. It should also work on 9i, or any version of Oracle that runs on Unix.

Instead of piping the export file directly into the unix compress utility, create a named pipe with the mkfifo command and specify that as the name of the export file. Prior to starting the export, run a compress command in background that reads from the named pipe and writes to a regular file. That file will be created compressed on the fly.

To import from the compressed file to just the opposite. Create a named pipe and use zcat or uncompress in background to read from the compressed file and redirect the output to the named pipe. Then start the import utility and specify the named pipe as the import file.

This tip is useful because it allows you to created compressed export files directly without first having to run the export then compress the output file. To do it the traditional way requires enough disk space to hold both the compressed and uncompressed files simultaneously. My method bypasses the uncompressed file altogether.

To export to a compressed file:

mkfifo pipe.dmp
compress < pipe.dmp > expdat.dmp.Z &
exp user/passwd full=y file=pipe.dmp
To import the same file:
mkfifo pipe.dmp
uncompress < expdat.dmp.Z > pipe.dmp &
imp user/passwd full=y file=pipe.dmp

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This was first published in October 2002

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