sysctl: Kernel Parameter Tuning#

The sysctl interface exposes kernel parameters that control how Linux manages memory, networking, file systems, and processes. Changes take effect immediately but are lost on reboot unless persisted.

Memory Parameters#

# Reduce swap aggressiveness (default is 60, range 0-100)
# Lower values make the kernel prefer reclaiming page cache over swapping
# Set to 10 for database servers -- swapping destroys database performance
sysctl -w vm.swappiness=10

# Overcommit behavior
# 0 = heuristic overcommit (default, kernel estimates if there is enough memory)
# 1 = always overcommit (never refuse malloc -- dangerous but used by Redis)
# 2 = strict overcommit (never allocate more than swap + ratio*physical)
sysctl -w vm.overcommit_memory=0

The vm.swappiness parameter is one of the most impactful settings for database servers. The default of 60 means the kernel will fairly aggressively swap application memory to disk in favor of filesystem cache. For databases that manage their own caching (PostgreSQL shared_buffers, MySQL innodb_buffer_pool), this is counterproductive – the database’s carefully managed cache gets swapped out to make room for OS-level cache the database does not use.