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System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

1. Clarify and agree on the scope of the system

• User cases (description of sequences of events that, taken together, lead to a system doing something useful)
  • Who is going to use it?
  • How are they going to use it?

Foredoomed

#参考：https://github.com/vipshop/vjtools/blob/master/vjstar/src/main/script/jvm-options/jvm-options.sh
#      http://calvin1978.blogcn.com/articles/jvmoption-7.html


# Base settings and GC logging
-server 
-XX:+AlwaysPreTouch  # First should be default, but we make it explicit, second pre-zeroes memory mapped pages on JVM startup -- improves runtime performance
# -Xloggc:gc-%t.log  # CUSTOMIZE LOCATION HERE - $path/gc-%t.log -- the %t in the gc log file path is so we get a new file with each JVM restart
-XX:NumberOfGCLogFiles=5 -XX:+UseGCLogFileRotation -XX:GCLogFileSize=20m # Limits the number of files, logs to folder 
-XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintHeapAtGC -XX:+PrintGCCause

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tmux cheat sheet

(C-x means ctrl+x, M-x means alt+x)

Prefix key

The default prefix is C-b. If you (or your muscle memory) prefer C-a, you need to add this to ~/.tmux.conf:

remap prefix to Control + a

Foredoomed

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

Foredoomed

// XXX should be standard (and named clone, after Java?)
Object.prototype.copy = function () {
    let o = {}
    for (let i in this)
        o[i] = this[i]
    return o
}

// Containment testing for arrays and strings that should be coherent with their iterator.
Array.prototype.contains = String.prototype.contains = function (e) {