-.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).
+.rsync-tmp dir for partial transfers. The only time that the --partial
+option does not look for this environment value is (1) when --inplace was
+specified (since --inplace conflicts with --partial-dir), or (2) when
+--delay-updates was specified (see below).
+
+dit(bf(--delay-updates)) This option puts the temporary file from each
+updated file into the file's partial-dir (see above) 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. If you don't specify the --partial-dir option, this option will
+cause it to default to ".~tmp~" (RSYNC_PARTIAL_DIR is not consulted for
+this value). Conflicts with --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 --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 --link-dest and a
+parallel hierarchy of files).