This can substantially reduce the cost of notmuch new in some situations, such as when the file system cache is cold or when the Maildir is on NFS. --- notmuch-new.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)
diff --git a/notmuch-new.c b/notmuch-new.c index faa33f1..364c73a 100644 --- a/notmuch-new.c +++ b/notmuch-new.c @@ -323,6 +323,26 @@ add_files (notmuch_database_t *notmuch, } db_mtime = directory ? notmuch_directory_get_mtime (directory) : 0; + /* If the directory is unchanged from our last scan and has no + * sub-directories, then return without scanning it at all. In + * some situations, skipping the scan can substantially reduce the + * cost of notmuch new, especially since the huge numbers of files + * in Maildirs make scans expensive, but all files live in leaf + * directories. + * + * To check for sub-directories, we borrow a trick from find, + * kpathsea, and many other UNIX tools: since a directory's link + * count is the number of sub-directories (specifically, their + * '..' entries) plus 2 (the link from the parent and the link for + * '.'). This check is safe even on weird file systems, since + * file systems that can't compute this will return 0 or 1. This + * is safe even on *really* weird file systems like HFS+ that + * mistakenly return the total number of directory entries, since + * that only inflates the count beyond 2. + */ + if (directory && fs_mtime == db_mtime && st.st_nlink == 2) + goto DONE; + /* If the database knows about this directory, then we sort based * on strcmp to match the database sorting. Otherwise, we can do * inode-based sorting for faster filesystem operation. */ -- 1.8.4.rc3