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Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

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create schema shard_1;  
create sequence shard_1.global_id_sequence;

CREATE OR REPLACE FUNCTION shard_1.id_generator(OUT result bigint) AS $$  
DECLARE  
    our_epoch bigint := 1314220021721;
    seq_id bigint;
    now_millis bigint;
    -- the id of this DB shard, must be set for each
    -- schema shard you have - you could pass this as a parameter too

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Scaling your API with rate limiters

The following are examples of the four types rate limiters discussed in the accompanying blog post. In the examples below I've used pseudocode-like Ruby, so if you're unfamiliar with Ruby you should be able to easily translate this approach to other languages. Complete examples in Ruby are also provided later in this gist.

In most cases you'll want all these examples to be classes, but I've used simple functions here to keep the code samples brief.

Request rate limiter

This uses a basic token bucket algorithm and relies on the fact that Redis scripts execute atomically. No other operations can run between fetching the count and writing the new count.

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// demo_cpu.c

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

#define ISROM(a) ((a) < 16)
#define ISRAM(a) ((a) >= 16 && (a) < 20)

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These instructions will explain how to install tensorflow on mac with cuda enabled GPU suport. I assume you know what tensorflow is and why you would want to have a deep learning framework running on your computer.

Prerequisites

Make sure to update your homebrew formulas

brew update

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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

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# Rename tags named foo-bar-#.#.# to v#.#.# and push the tag changes
git tag -l | while read t; do n="v${t##*-}"; git tag $n $t; git push --tags ; git tag -d $t; git push origin :refs/tags/$t ; done

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title	description	date	categories	slug
QQ协议分析	QQ协议分析	2014-04-16	protocol	qq-protocol

一. 文字聊天协议族(TCPF, Text Chatting Protocol Family)

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#!/bin/bash
#
# chkconfig: 2345 55 25
# description: Openresty
# processname: nginx
# config: /usr/local/openresty/nginx/conf/nginx.conf
# pidfile: /usr/local/openresty/nginx/logs/nginx.pid
### BEGIN INIT INFO
# Provides: nginx
# Required-Start: $local_fs $remote_fs $network $named $syslog $time

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#! /usr/bin/env python

import redis
import random
import pylibmc
import sys

r = redis.Redis(host = 'localhost', port = 6389)
mc = pylibmc.Client(['localhost:11222'])