Stuart Inglis
5ecab683a8
write_file()'s sparse path sliced each span into SPARSE_WRITE_SIZE (1024-byte) pieces and write_sparse() issued one write() syscall per slice. Copying a large *non-sparse* file with --sparse therefore cost roughly one write() per kilobyte -- about a million write() calls for a 1 GiB file -- which on real storage ran far slower than the same copy without --sparse (the bug report measured 1.36 MB/s vs 391 MB/s, ~280x). The 1024-byte chunk is also smaller than a filesystem block, so it cannot even create finer holes than a plain copy could. Rewrite write_sparse() to scan the whole span itself: it looks for interior runs of zeros that are at least SPARSE_WRITE_SIZE long -- the same hole granularity rsync has always used -- and emits each intervening non-zero region (which may include shorter zero runs not worth a hole) with a single write(). do_punch_hole() advances the file offset just like the lseek() path, so flushing a deferred hole between segments keeps the position correct. The hole granularity is unchanged, so sparseness is identical; only the syscall pattern changes. Measured on a 100 MiB random (hole-free) file: write() syscalls drop from 100,730 to 6,125 (~16x), now tracking the data's natural chunking rather than its size in kilobytes. Verified byte-identical and equally sparse output for hole-free, large-hole, small-interior-hole, all-zero, --inplace, and --preallocate cases. testsuite/sparse-write-count_test.py copies a 16 MiB hole-free file under strace and asserts the write() count stays far below the old size/1024 behaviour (it skips where strace is unavailable).
WHAT IS RSYNC?
Rsync is a fast and extraordinarily versatile file copying tool for both remote and local files.
Rsync uses a delta-transfer algorithm which provides a very fast method for bringing remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand. At first glance this may seem impossible because the calculation of diffs between two files normally requires local access to both files.
A technical report describing the rsync algorithm is included with this package.
USAGE
Basically you use rsync just like scp, but rsync has many additional options. To get a complete list of supported options type:
rsync --help
See the manpage for more detailed information.
BUILDING AND INSTALLING
If you need to build rsync yourself, check out the INSTALL page for information on what libraries and packages you can use to get the maximum features in your build.
SETUP
Rsync normally uses ssh or rsh for communication with remote systems. It does not need to be setuid and requires no special privileges for installation. You must, however, have a working ssh or rsh system. Using ssh is recommended for its security features.
Alternatively, rsync can run in `daemon' mode, listening on a socket. This is generally used for public file distribution, although authentication and access control are available.
To install rsync, first run the "configure" script. This will create a Makefile and config.h appropriate for your system. Then type "make".
Note that on some systems you will have to force configure not to use gcc because gcc may not support some features (such as 64 bit file offsets) that your system may support. Set the environment variable CC to the name of your native compiler before running configure in this case.
Once built put a copy of rsync in your search path on the local and remote systems (or use "make install"). That's it!
RSYNC DAEMONS
Rsync can also talk to "rsync daemons" which can provide anonymous or authenticated rsync. See the rsyncd.conf(5) manpage for details on how to setup an rsync daemon. See the rsync(1) manpage for info on how to connect to an rsync daemon.
WEB SITE
For more information, visit the main rsync web site.
You'll find a FAQ list, downloads, resources, HTML versions of the manpages, etc.
MAILING LISTS
There is a mailing list for the discussion of rsync and its applications that is open to anyone to join. New releases are announced on this list, and there is also an announcement-only mailing list for those that want official announcements. See the mailing-list page for full details.
DISCORD
There is also an rsync Discord server for real-time chat about rsync and its development.
BUG REPORTS
The bug-tracking web page has full details on bug reporting.
That page contains links to the current bug list, and information on how to do a good job when reporting a bug. You might also like to try searching the Internet for the error message you've received, or looking in the mailing list archives.
To send a bug report, follow the instructions on the bug-tracking page of the web site.
Alternately, email your bug report to rsync@lists.samba.org.
For security issues please email details of the issue to rsync.project@gmail.com.
GIT REPOSITORY
If you want to get the very latest version of rsync direct from the source code repository, then you will need to use git. The git repo is hosted on GitHub and on Samba's site.
See the download page for full details on all the ways to grab the source.
COPYRIGHT
Rsync was originally written by Andrew Tridgell and Paul Mackerras. Many people from around the world have helped to maintain and improve it.
Rsync may be used, modified and redistributed only under the terms of the GNU General Public License, found in the file COPYING in this distribution, or at the Free Software Foundation.