If you are looking for something advanced, you should check books written by C. J. Date. For example, his "An Introduction to Database Systems" considered as one of the best book on database theory.
After dropping btrfs support some time ago they started developing their own next-gen file system based on LVM and XFS.
It is now available for technology preview on Fedora 28.
Actually, it is quite opposite. ZFS is a copy-on-write filesystem - if you do write in the middle of your file the datablock gets moved to a new place on your disk.
For typical database load your db files get more and more fragmented with time.
On my previous job we had to manage thousands of customer domains, including annual renewal.
This was very tedious task, so I wrote a Perl script, scraping WHOIS and DNS data for all domains listed on our DNS servers. Based on this data every domain was assigned a status, such as "Ok", "misconfigured", "about to expire", "points to foreign DNS server" or "points to foreign Web server". This script was scheduled to run every other day and sent CSV report (full and diff from previous run) to a person responsible for domain renewal.
Needless to say, our support specialists were very happy with this improvement.