500ms to 2.5 seconds • Disabling the PHP setting default_socket_timeout Operating System • Disabling SYN cookies on the host systems • Checking the number of file descriptors on Redis and Webservers • Raising the mbuffer of the host systems • Control and adjust the TCP backlog sizes
limit was reached ... • allkeys-lru: [...] less recently used (LRU) keys ﬁrst • volatile-lru: [...] less recently used (LRU) keys ﬁrst (with TTL) • allkeys-random: evict random keys ... • volatile-random: evict random keys (with TTL) • volatile-ttl: [...] evict keys with an expire set, with a shorter time to live (TTL) ﬁrst.
simple, but actually, like any tool used in critical contexts, there are two possibilities: 1) Know how it works very well and do great things with it. 2) Don't understand it properly and find yourself in big troubles soon or later. antirez HackerNews, 31. March 2017