On Thu, Jul 2, 2020 at 10:29 PM Scott Schmit <i.grok@xxxxxxxxxxx> wrote: > > On Sun, Jun 28, 2020 at 03:40:11PM -0600, Chris Murphy wrote: > > Databases and VM images are things btrfs is bad at out of the box. > > Most of this has to do with fsync dependency of other file systems. > > Btrfs is equipped to deal with an fsync heavy world out of the box, > > using treelog enabled by default. But can still be slow for some > > workloads. > > Does this also impact mariadb databases? I've noticed that since > reinstalling my machine with mediawiki installed, the performance of the > wiki has dropped noticeably when the cache is cold (just loading the > pages, not editing them). Good question. A complete answer leads to a lot more questions. Mariadb has a couple older docs on this: one suggests using 'noatime' mount option on all file systems [1] as an optimization, and additionally for Btrfs to use 'nodatacow' [2]. It can be set per directory or per file using 'chattr +C' before files are created - it won't work after the fact. 'chattr +C' will make files behave like it's on any other filesystem: all writes are overwrites instead of copy-on-write, no checksums, no compression. Is this stale information? Is there something unrelated going on in your case? Should databases setup these optimizations on behalf of users? Does storage type make a difference? I'm just going to set those aside for now. To give the nodatacow suggestion a try: ## shutdown the database # mkdir /var/lib/mysql2 # chattr +C /var/lib/mysql2 # cp /var/lib/mysql/* /var/lib/mysql2/ # rm /var/lib/mysql/ # mv /var/lib/mysql2/ /var/lib/mysql/ ## resume operation Advanced topic is what happens if you take a snapshot of a subvolume that includes files set to nodatacow. Short answer: you can, and it's fine. Long answer: initially this will cause datacow to resume but still without checksums and compression, new writes are temporarily datacow, subsequent writes are nodatacow. This behavior is the same as if the nodatacow file had been reflink copied, either on Btrfs or XFS. [1] https://mariadb.com/kb/en/filesystem-optimizations/ [2] https://mariadb.com/resources/blog/what-is-the-best-linux-filesystem-for-mariadb/ -- Chris Murphy _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
