How zcat works?

UNIX for Beginners Q & A UNIX for Dummies Questions & Answers
1

Hi,

just i would like to know, how will be the response if you try to read a 40GB compressed file using zcat.
a)Uncompress the 40GB file and have it in the disk. use cat to view the steps.
b)Use zcat directly to view the compressed file?

What are the steps being occurred in step (b)?
Where does actual compression takes place?
Which one is the best way to handle this scenario?

Thanks

2

Daily I works with .gz files, so I always need to use zcat .

I normally don't have a file with 40GB. I'll be having around 25-50 files of size 20-30 MB.

so I use.

zcat *.gz | #choose what i want to do.

But the important question is what you are trying to achieve with that file..?

3

Hi Pamu,
Thanks for your response.
Just i wanted to know, whether zcat is recommended for large files(more than 40GB).
I wanted to implement compressed loading in oracle while using external table load strategy.
For that i need to have zcat in bin directory. just i suspect how zcat will behave for huge files.
And also i want to understand the internal implementation of zcat.
i believe zcat should un-compress the original file intermediately somewhere and read.
although we don't see any impact in small files, i want to make sure the impact for the huge files.

thanks

4

Yes. It uses temp memory to perform un compression work.

So the impact might be how much load it will ask to do the things. I believe while performing zcat oparations on a big file, there is large chances that system will throw low memory space error.