peng weikang pengwk

System Design Cheatsheet

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

Basic Steps

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?

注意：本文内容适用于 Tmux 2.3 及以上的版本，但是绝大部分的特性低版本也都适用，鼠标支持、VI 模式、插件管理在低版本可能会与本文不兼容。

Tmux 快捷键 & 速查表 & 简明教程

启动新会话：

tmux [new -s 会话名 -n 窗口名]

恢复会话：

Adventures in Python Core Dumping

After watching Bryan Cantrill's presentation on [Running Aground: Debugging Docker in Production][aground] I got all excited (and strangely nostalgic) about the possibility of core-dumping server-side Python apps whenever they go awry. This would theoretically allow me to fully inspect the state of the program at the point it exploded, rather than relying solely on the information of a stack trace.

Here are my attempts to script an IntelliJ-based IDE using javax.script.* API (ex-JSR-223).

The list of available scripting languages and engines:

Groovy - built-in, via Groovy jars and <app>/lib/groovy-jsr223-xxx.jar
JavaScript (Nashorn) - built-in, via Java Runtime <app>/jbr/... (deprecated and will be removed soon)
JavaScript (GraalJS) - https://plugins.jetbrains.com/plugin/12548-intellij-scripting-javascript
JPython - https://plugins.jetbrains.com/plugin/12471-intellij-scripting-python
JRuby - https://plugins.jetbrains.com/plugin/12549-intellij-scripting-ruby
Clojure - https://plugins.jetbrains.com/plugin/12469-intellij-scripting-clojure

some tools for diagrams in software documentation

Diagrams For Documentation

Obvious Choices

ASCII

PSQL

Magic words:

psql -U postgres

Some interesting flags (to see all, use -h or --help depending on your psql version):

-E: will describe the underlaying queries of the \ commands (cool for learning!)
-l: psql will list all databases and then exit (useful if the user you connect with doesn't has a default database, like at AWS RDS)

Moved to git repository: https://github.com/denji/nginx-tuning

NGINX Tuning For Best Performance

For this configuration you can use web server you like, i decided, because i work mostly with it to use nginx.

Generally, properly configured nginx can handle up to 400K to 500K requests per second (clustered), most what i saw is 50K to 80K (non-clustered) requests per second and 30% CPU load, course, this was 2 x Intel Xeon with HyperThreading enabled, but it can work without problem on slower machines.

You must understand that this config is used in testing environment and not in production so you will need to find a way to implement most of those features best possible for your servers.

	# coding: utf-8

	"""Extract entries from GetText (.po) file.

	usage:

	print __script__ in.po filter.txt > out.po

	- standard input: not used.
	- standard output: filtered po file content.

	根据Unicode5.0整理如下：

	1）标准CJK文字
	http://www.unicode.org/Public/UNIDATA/Unihan.html

	2）全角ASCII、全角中英文标点、半宽片假名、半宽平假名、半宽韩文字母：FF00-FFEF
	http://www.unicode.org/charts/PDF/UFF00.pdf

	3）CJK部首补充：2E80-2EFF
	http://www.unicode.org/charts/PDF/U2E80.pdf

	# source: http://stackoverflow.com/questions/1317714/how-can-i-filter-a-date-of-a-datetimefield-in-django

	from django.utils import timezone

	today_min = datetime.datetime.combine(timezone.now().date(), datetime.time.min)
	today_max = datetime.datetime.combine(timezone.now().date(), datetime.time.max)
	MyModel.objects.get(date__range=(today_min, today_max))