-variable. Setting this in the environment does not force --partial to be
-enabled, but rather it effects where partial files go when --partial (or
--P) is used. For instance, instead of specifying --partial-dir=.rsync-tmp
-along with --progress, you could set RSYNC_PARTIAL_DIR=.rsync-tmp in your
-environment and then just use the -P option to turn on the use of the
-.rsync-tmp dir for partial transfers. The only time the --partial option
-does not look for this environment value is when --inplace was also
-specified (since --inplace conflicts with --partial-dir).
+variable. Setting this in the environment does not force bf(--partial) to be
+enabled, but rather it effects where partial files go when bf(--partial) is
+specified. For instance, instead of using bf(--partial-dir=.rsync-tmp)
+along with bf(--progress), you could set RSYNC_PARTIAL_DIR=.rsync-tmp in your
+environment and then just use the bf(-P) option to turn on the use of the
+.rsync-tmp dir for partial transfers. The only time that the bf(--partial)
+option does not look for this environment value is (1) when bf(--inplace) was
+specified (since bf(--inplace) conflicts with bf(--partial-dir)), or (2) when
+bf(--delay-updates) was specified (see below).
+
+For the purposes of the server-config's "refuse options" setting,
+bf(--partial-dir) does em(not) imply bf(--partial). This is so that a
+refusal of the bf(--partial) option can be used to disallow the overwriting
+of destination files with a partial transfer, while still allowing the
+safer idiom provided by bf(--partial-dir).
+
+dit(bf(--delay-updates)) This option puts the temporary file from each
+updated file into a holding directory until the end of the
+transfer, at which time all the files are renamed into place in rapid
+succession. This attempts to make the updating of the files a little more
+atomic. By default the files are placed into a directory named ".~tmp~" in
+each file's destination directory, but you can override this by specifying
+the bf(--partial-dir) option. (Note that RSYNC_PARTIAL_DIR has no effect
+on this value, nor is bf(--partial-dir) considered to be implied for the
+purposes of the server-config's "refuse options" setting.)
+Conflicts with bf(--inplace).
+
+This option uses more memory on the receiving side (one bit per file
+transferred) and also requires enough free disk space on the receiving
+side to hold an additional copy of all the updated files. Note also that
+you should not use an absolute path to bf(--partial-dir) unless there is no
+chance of any of the files in the transfer having the same name (since all
+the updated files will be put into a single directory if the path is
+absolute).
+
+See also the "atomic-rsync" perl script in the "support" subdir for an
+update algorithm that is even more atomic (it uses bf(--link-dest) and a
+parallel hierarchy of files).