This is your database on Linux

Transcript

1. THIS IS YOUR DATABASE ON LINUX @SAMKOTTLER
2. ABOUT ME ▸ Platform engineering @ DigitalOcean ▸ Formerly of Red Hat & Venmo ▸ Committer to CentOS, Fedora, Icinga, Ansible
3. PROFESSIONALLY CAREMAD AT OS'S
4. WHAT WE'LL COVER ▸ Memory ▸ Disk ▸ Network
5. MEMORY
6. VM.SWAPPINESS ▸ Instructs the OS about when to swap ▸ Default value of 60 ▸ Set this to 0
7. "My point is that decreasing the tendency of the kernel to swap stuff out is wrong. You really don't want hundreds of megabytes of BloatyApp's untouched memory floating about in the machine. Get it out on the disk, use the memory for something useful." - Andrew Morton
8. TRANSPARENT HUGE PAGES ▸ Intended to keep fewer entries in the TLB ▸ Hands out 2M or 1G pages on malloc() ▸ Breaks when paired with madvise(), particularly with jemalloc ▸ Disable THP
9. BIT.LY/DO-ALLOCATORS
10. DIRTY RATIO ▸ vm.dirty_background_ratio: start flushing to disk ▸ vm.dirty_ratio: require synchronous I/O ▸ /proc/vmstat should be carefully monitored
11. NUMA ▸ Unlike UMA, NUMA means that memory is addressed per-CPU ▸ Modern systems generally have 2+ NUMA nodes ▸ Local operations on a CPU will cause swapping, even if memory is available. ▸ /usr/bin/numactl --interleave all <cmd>
12. DISK
13. FILESYSTEMS ▸ ext4 is still a very safe bet ▸ xfs has had performance issues, largely solved now ▸ btrfs is interesting
14. YEAH, SO DON'T RUN BTRFS
15. SPINNING DISKS ▸ Mostly just don't, except for cold storage ▸ CFQ/elevator is a good bet
16. SSD'S ▸ Use them, they're generally okay ▸ Don't run multi-threaded workloads on consumer grade drives ▸ deadline/noop scheduler
17. MORE BITS ON SSD'S ▸ Controller firmware quality is generally bad ▸ Did I mention controller firmware quality is low? ▸ Your drives might just sometimes die because of firmware ▸ Find a working firmware release, rarely change versions
18. NVME ▸ Non-volatile memory via PCIe ▸ SATA/SAS/Fibre channel are too slow for high-end flash ▸ Currently economical for use as read through/write back cache ▸ Supported in Linux since 3.3
19. NETWORK
20. TCP METRICS ▸ Stores information about congestion and window size for like 1k connections. ▸ Windows size and congestion information based on previous conditions. ▸ Set net.ipv4.tcp_no_metrics_save to 1.
21. FIN TIMEOUT ▸ Determines how long to wait for a FIN ▸ Set net.ipv4.tcp_fin_timeout to something below 60
22. OTHER CHANGES ▸ Disable SYN cookies ▸ ECN
23. THANKS! ▸ shk@linux.com ▸ github.com/skottler