inotify and rsync on large number of files

Question

I am using inotify to watch a directory and sync files between servers using rsync. Syncing works perfectly, and memory usage is mostly not an issue. However, recently a large number of files were added (350k) and this has impacted performance, specifically on CPU. Now when rsync runs, CPU usage spikes to 90%/100% and rsync takes long to complete, there are 650k files being watched/synced.

Is there any way to speed up rsync and only rsync the directory that has been changed? Or alternatively to set up multiple inotifywaits on separate directories. Script being used is below.

UPDATE: I have added the --update flag and usage seems mostly unchanged

#! /bin/bash

EVENTS="CREATE,DELETE,MODIFY,MOVED_FROM,MOVED_TO"

inotifywait -e "$EVENTS" -m -r --format '%:e %f' /var/www/ --exclude '/var/www/.*cache.*' | (
WAITING="";
while true; do
    LINE="";
    read -t 1 LINE;
    if test -z "$LINE"; then
        if test ! -z "$WAITING"; then
                echo "CHANGE";
                WAITING="";
                rsync --update -alvzr --exclude '*cache*' --exclude '*.git*' /var/www/* root@secondwebserver:/var/www/
        fi;
    else
        WAITING=1;
    fi;
done)

Answer 1

If the server has a slow processor avoid checksums and compression with rsync. I would remove ht "-z" option in the rsync command.

rsync --update -alvr --exclude '*cache*' --exclude '*.git*' /var/www/* root@secondwebserver:/var/www/

Note that it will not avoid rsync to compare the 650k files. You could rsync subdirectories of /var/www one by one to reduce the number of files checked at one time.

Answer 2

Thank you for posting your answer - it really helped me. I think you can simplify the loop:

EVENTS="CREATE,DELETE,MODIFY,MOVED_FROM,MOVED_TO"

sync() {
  rsync --update -alvzr --exclude '*cache*' --exclude '*.git*' /var/www/* root@secondwebserver:/var/www/

}
watch() {
  inotifywait -e "$EVENTS" -m -r --format '%:e %f' /var/www/ --exclude '/var/www/.*cache.*' 
}


watch | (
while true ; do
  read -t 1 LINE && sync
done
)

You may need to adjust that slightly but the gist should be clear. I'm using a variant with Amazon's AWS s3 sync, so I may have substituted your rsync command in incorrectly.

Answer 3

You might check this tool syncthing

I'm using dockerized version from this repo

I have 411k files to sync using this tool, I had some issues regarding file names encoding for some files named in arabic

#!/bin/bash
docker run -d --rm \
  --name=syncthing \
  -e PUID=1000 \
  -e PGID=1000 \
  -e TZ=Asia/Jordan \
  -e UMASK_SET=022 \
  -p 8384:8384 \
  -p 22000:22000 \
  -p 21027:21027/udp \
  -v "$(pwd)/config:/config" \
  -v "path_to_sync:/config/Sync" \
  --net host \
  linuxserver/syncthing

Note: use GUI to configure