On Sat, Jan 22, 2011 at 5:41 PM, Clemens Eisserer [off-list ref] wrote:

quoted

E.g. suppose you have a LZO compressed file, then a program rewrites some
data which is in the middle of the file, and suppose the newly written data
is less compressible.

Any idea how this is handled? I would be interested in the answer as well.

Thank you in advance, Clemens

The same way any write is handled:  the data is written elsewhere.
Compression isn't special in this regard.