rsync very slow with large include/exclude file list
rsync-list-m829 at sizone.org
Mon Jun 15 17:08:05 MDT 2015
This is similar to using fuzzy / -y in a large directory. O(n^2) behaviour
occurs and can be incredibly slow. No caching of md5's for the directory
occurs, it would seem (or even so, there are O(N^2) comparisons).
On Mon, Jun 15, 2015 at 06:02:14PM -0500, ray vantassle said:
> I investigated the rsync code and found the reason why.
> For every file in the source, it searches the entire filter-list looking
> to see if that filename is on the exclude/include list.** Most aren't, so
> it compares (350K - 72K) * 72K names (the non-listed files) plus (72K *
> 72K/2) names (the ones that are listed), for a total of about**
> 22,608,000,000 strcmp's.** That's 22 BILLION comparisons. (I may have left
> off a zero there, it might be 220 B).
> I'm working on a fix to improve this.** The first phase was to just
> improve the existing code without changing the methodology.
> The set I've been testing with is local-local machine, dry-run, 216K files
> in the source directory, 25,000 files in the exclude-from list.
> The original rsync takes 488 seconds.
> The improved code takes 300 seconds.
> The next phase was to improve the algorithm of handling large
> filter_lists.** Change the unsorted linear search to a sorted binary
> search (skiplist).
> This improved code takes 2 seconds.
> The original code does 4,492,304,682 strcmp's.
> The fully improved code does 6,472,564.** 98.5% fewer.
> I am cleaning up the code and will submit a patchfile soon.
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