The experiments are over, and the results were not success.
Having two filesystems cohabiting in the same hash table results in a
lot of false positives, each of which requires some heavy IO to resolve.
Using MAP_SHARED to share a beeshash.dat between processes results in
catastrophically bad performance.
These features were abandoned long ago, but some of the code--and even
worse, its documentation--still remains.
Bees wants a hash table false positive rate below 0.1%. With a shared
hash table the FP rate is about the same as the dedup rate. Typically
duplicate files on one filesystem are duplicate on many filesystems.
One or more of Linux VFS and the btrfs mmap(MAP_SHARED) implementation
produce extremely poor performance results. A five-order-of-magnitude
speedup was achieved by implementing paging in userspace with worker
threads. We no longer need the support code for the MAP_SHARED case.
It is still possible to run many BeesContexts in a single process,
but now the only thing contexts share is the FD cache.
Allow relative paths with BEESHOME. These paths will be relative
to the root of the dedup target filesystem.
BEESHOME is now optional. If not specified, '.beeshome' is used.
We don't try to create BEESHOME if it doesn't exist. BEESHOME might
not be on a btrfs filesystem, so we can't insist it be a subvol.
BeesHashTable can now create a beeshash.dat if the file does not already
exist. Currently the default size is one hash table extent (16MB) and
there's no way to change that (yet), so users should still create their
own hash tables for now.
The opening of the hash table is deferred (slightly) in preparation for
hash table resizing.
No doc as the feature is currently unfinished.
I got a little too enthusiastic when redacting the code, and removed some
overloaded functions bees was using. C++ silently found replacements,
and the result was a bug that prevented any data from being persisted
from the hash table.
Fixes: https://github.com/Zygo/bees/issues/7
I accidentally did a pre-push verification on a 32-bit build host.
There were a surprisingly small number of problems, so fix them.
Bees now builds on a 32-bit host. Let's not update README just yet,
though: the 32-bit ioctl support fails immediately after startup on a
64-bit kernel.
"agent" is a nice generic term for the set of things that userspace
btrfs deduplicators are. Let's call it that.
Throw out the awkward and rambling "About" text and use the announcement
from linux-btrfs instead. Terrible English writing I at am.
I'm not surprised that GCC 6 doesn't let me send an ostream ref to itself,
even inside an uninstantiated template specialization. I am a little
surprised I was trying to, and 4.9 let me get away with it.
It's 2016. auto_ptr is deprecated now.
Some things were including vector that don't any more.
https://github.com/Zygo/bees/issues/1
