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Many UNIX variants used system calls that operated on files
with 32-bit unsigned integers to indicate file offset. Unfortunately, 32-bit
unsigned integers are limited to a range of 0 to 2 gigabytes.

When UNIX systems began accepting files that were larger than
the 2 GB maximum, it required applications and utilities to use alternate
system calls, such as fseek64, to operate on these large files. This decision
was made to avoid breaking older programs, which still used 32-bit integers,
and the original system calls without needing to be recompiled.

The Oracle import and export utilities were written with the
original system calls, internally. This meant that you could not export or
import a file larger than 2 GB on a UNIX system unless you used some tricks to
split the file into pieces less than 2 GB.

Before Oracle 8i,
you could use the split command and
named pipes to write the output of exp
to multiple files. The split command
would take standard input and write its output to multiple files, switching to
a new file whenever a limit was reached. For example:

mknodpipe.dmp p
split -b 2047m < pipe.dmp &
exp system/manager file=pipe.dmp full=y

This process would create files called xaa, xab, xac, and so on. To import these
files, you could run the commands:

mknodpipe.dmp p
cat xaaxabxac > pipe.dmp &
imp system/manager file=pipe.dmp full=y

Since Oracle 8i,
Oracle added a command-line parameter filesize, which does something similar to the split command. It automatically creates
the export as a set of files instead of a single file. It’s important to make
sure that the value for filesize
is less than 2 GB. It’s also important to specify the same parameter on import:

exp system/manager file=big.dmpfilesize=2000M full=y
imp system/manager file=big.dmpfilesize=2000M full=y

Since an export file is fairly compressible, you can still
use the split trick to export a file up to around 10 GB and stay under the 2 GB

mknodpipe.dmp p
compress < pipe.dmp > expdat.dmp.Z &
exp system/manager file=pipe.dmp full=y

Here’s the code to import a file:

mknodpipe.dmp p
uncompress expdat.dmp.Z > pipe.dmp &
imp system/manager file=pipe.dmp full=y
rm pipe.dmp