"
Refs #3929
Enables re-use of commitlog segments.
First, ensures we never succeed playing back a commitlog
segment with name not matching the ID:s in the actual
file data, by determining expected id based on file name.
This will also handle partially written re-used files, as
each chunk headers CRC is dependent on the ID, and will
fail once we hit any left-overs.
Second part renamed and puts files into a recycle list
instead of actually deleting them when finished.
Allocating new files will the prioritize this list
before creating a new file.
Note that since consumtion and release of segments can
be somewhat unbalanced, this does not really guarantee
we will use recycled files even in all cases when it
might be possible, simply because of timing. It does
however give a good chance of it.
We limit recycled files based on the max disk size
setting, thus we can potentially grow disk size
more than without depending on timing, but not
uncontrolled.
While all this theoretially might improve disk
writes in some cases, it is far from any magic bullet.
No real performance testing has been done yet, only
functional.
"
* 'calle/commitlog-reuse' of github.com:scylladb/seastar-dev:
commitlog: Recycle used segments instead of delete + new file
commitlog: Terminate all segments with a zero chunk
commitlog_replay: Enforce file name based id matching
904db433d9