= Performance =

== performance issues with mutable files ==

Tahoe-LAFS can create mutable files of arbitrary size. There are good
reasons to not overuse these.

When you first create a mutable file, Tahoe-LAFS generates an RSA
keypair to associate with the file. This takes about a second on an
ordinary desktop PC (and possibly considerably longer on specialized or
embedded hardware). The cost of key generation is probably irrelevant if
you only use a few mutable files, but can quickly add up if you want to
create a lot of them.

Part of the process of encrypting, encoding, and uploading a mutable
file to a Tahoe-LAFS grid requires that the entire file be loaded into
memory at once. For larger files, this may cause Tahoe-LAFS to have an
unacceptably large memory footprint (at least when uploading your
mutable file).

As currently implemented, small modifications to mutable files are no
less expensive than large modifications; in both cases, the process
described above (with the performance concerns described above) must be
repeated for the entire file. 

We are exploring ways to address at least some of these problems. In the
meantime, however, it is a good practice to not overuse mutable files,
and to not create exceptionally large mutable files. For more
information on how mutable files are currently implemented, see the
mutable file specification, in docs/specifications/mutable.txt.