Friday, August 25, 2006

dumpfile diving

The oracle EXP utility generates a dumpfile which, although technically binary, actually contains lots of readable ASCII. Sometime I need to see this information, especially since dumpfiles don't provide a way (that I know of) of summarizing their contents and the conditions of their generation. In a perfect world, we'd never have to work from with dumpfiles burned onto scratched CDs by unknown parties and abandoned in the dusty corner behind the recycle bin, but this is not a perfect world.

Anyway, I just went through several techniques of examining a mysterious.dmp, and thought I'd share the experience. Much of it would apply to delving into any mixed binary/ascii file.
  • The worst way: more mysterious.dmp

    gave me frightening glyphs and angry beeps (xset b off to stop those), like R2-D2 invoking dread Cthulhu. Worse, my session would henceforth speak to me only in proto-Sumerian. I could kill the terminal window and open a new one, of course, but I still spent several hours plastering smooth curves over all the office's sharp corners, just to be safe.

  • Not quite so bad: less mysterious.dmp

    let me look at the file, making harmless marks of the binary characters, and didn't mangle my session's character set. Yay! I do need to make a habit of using less instead of more.

  • Still pretty painful: grep -a "what I'm looking for" mysterious.dmp

    The -a flag makes grep look into a file even though it's binary. It has no proper idea of where lines end in a binary file, though, so your hits can be really long. I had better luck grepping the files that resulted from the operations below.

  • Good: imp me@mydb show=Y file=mysterious.dmp full=y log=mysterious_contents.txt

    This gives you a clean-looking file (well, except for all the gratuitous quotation marks). It's also the only technique I know that you can use on Windows (without Cygwin). You don't get data contents, though, just DDL.

  • Best: strings mysterious.dmp > mysterious_contents.txt

    This GNU strings utility is really great! You get the ASCII, the whole ASCII, and nothing but the ASCII, quick and clean.
What I still don't have, though, is a way to examine a dumpfile and find out exactly what command was used to generate it. That would give all kinds of fantastic information: What instance was it? Which user did the export? Was it full? ... and so forth. If you know of a way to query a dumpfile for this kind of information, please comment!

1 comment:

Anonymous said...

Hi Catherine,

It's also the only technique I know that you can use on Windows (without Cygwin).

You can get native ports for Win32 of some Unix utilities (including grep, less, sed, gawk...but not strings :-( at: