[GitHub] [couchdb] ceremcem opened a new issue, #4227: CouchDB should provide advice on safe use with BTRFS storage

[GitBox <gi...@apache.org>]

ceremcem opened a new issue, #4227:
URL: https://github.com/apache/couchdb/issues/4227

   ## Summary
   
   BTRFS filesystem does not play well with database files due to its Copy-on-Write feature. This kind of files should be created inside a folder whose CoW feature is turned off. 
   
   See https://btrfs.wiki.kernel.org/index.php/Gotchas#Fragmentation
   
   > Files with a lot of random writes can become heavily fragmented (10000+ extents) causing thrashing on HDDs and excessive multi-second spikes of CPU load on systems with an SSD or large amount a RAM.
   On servers and workstations this affects databases and virtual machine images.
   
   Disabling CoW for "data" folder on a BTRFS filesystem would be a wise move. 
   
   ## Possible Solution
   
   Following script fixes the issue: 
   
   ```bash
   #!/bin/bash
   set -eu
   
   curr="/var/lib/couchdb"
   new="$curr.new"
   
   if lsattr $curr -a | grep /\.$ | grep -- "-C-" > /dev/null; then
       echo "CoW is already disabled for $curr. Doing nothing."
       exit 0
   fi
   systemctl stop couchdb
   mkdir $new
   chown couchdb:couchdb $new
   chattr +C $new
   rsync -avxHAX --info=progress2 $curr/ $new/
   mv $curr $curr.bak
   mv $new $curr
   systemctl start couchdb
   
   echo "---------------------------------------------"
   echo "Changes made successfully."
   echo "You can delete $curr.bak if everything works correctly."
   echo "---------------------------------------------"
   ```
   
   


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