From ....
The primary interface for tuning the Linux kernel is the /proc virtual filesystem. In recent years, the /sys filesystem has expanded on what /proc does. Shell scripts using echo and procedural code are difficult to manage automatically, as we all know from handling cassandra-env.sh. This led the distros to create /etc/sysctl.conf, and in modern distros, /etc/sysctl.conf.d. The sysctl command reads the files in /etc and applies the settings to the kernel in a consistent, declarative fashion.
The following is a block of settings I use almost every server I touch. Most of these are safe to apply live and should require little tweaking from site to site. Note: I have NOT tested these extensively with multi-DC, but most of them should be safe. Those items that may need extra testing for multi-DC have comments indicating it.
http://tobert.github.io/post/2014-06-24-linux-defaults.html
# The first set of settings is intended to open up the network stack performance by
# raising memory limits and adjusting features for high-bandwidth/low-latency
# networks.
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.core.netdev_max_backlog = 2500
net.core.somaxconn = 65000
net.ipv4.tcp_ecn = 0
net.ipv4.tcp_window_scaling = 1
net.ipv4.ip_local_port_range = 10000 65535
# this block is designed for and only known to work in a single physical DC
# TODO: validate on multi-DC and provide alternatives
net.ipv4.tcp_syncookies = 0
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 0
net.ipv4.tcp_fack = 1
net.ipv4.tcp_dsack = 1
net.ipv4.tcp_orphan_retries = 1
# significantly reduce the amount of data the kernel is allowed to store
# in memory between fsyncs
# dirty_background_bytes says how many bytes can be dirty before the kernel
# starts flushing in the background. Set this as low as you can get away with.
# It is basically equivalent to trickle_fsync=true but more efficient since the
# kernel is doing it. Older kernels will need to use vm.dirty_background_ratio
# instead.
vm.dirty_background_bytes = 10485760
# Same deal as dirty_background but the whole system will pause when this threshold
# is hit, so be generous and set this to a much higher value, e.g. 1GB.
# Older kernels will need to use dirty_ratio instead.
vm.dirty_bytes = 1073741824
# disable zone reclaim for IO-heavy applications like Cassandra
vm.zone_reclaim_mode = 0
# there is no good reason to limit these on server systems, so set them
# to 2^31 to avoid any issues
# Very large values in max_map_count may cause instability in some kernels.
fs.file-max = 1073741824
vm.max_map_count = 1073741824
# only swap if absolutely necessary
# some kernels have trouble with 0 as a value, so stick with 1
vm.swappiness = 1
On vm.max_map_count:
http://linux-kernel.2935.n7.nabble.com/Programs-die-when-max-map-count-is-too-large-td317670.html
limits.conf (pam_limits)
The DSE and DSC packages install an /etc/security/limits.d/ file by default that should remove most of the problems around pam_limits(8). Single-user systems such as database servers have little use for these limitations, so I often turn them off globally using the following in /etc/security/limits.conf. Some users may already be customizing this file, in which case change all of the asterisks to cassandra or whatever the user DSE/Cassandra is running as.
* - nofile 1000000
* - memlock unlimited
* - fsize unlimited
* - data unlimited
* - rss unlimited
* - stack unlimited
* - cpu unlimited
* - nproc unlimited
* - as unlimited
* - locks unlimited
* - sigpending unlimited
* - msgqueue unlimited
Linux
sysctl.conf
From ....
https://tobert.github.io/pages/als-cassandra-21-tuning-guide.html
Compare to what we have