MemSQL vs. MongoDB

	MemSQL	MongoDB
Category	Database	Database, Data Storage
Preference	75% votesvotes	25% votesvotes
Website	www.​memsql.​com	www.​mongodb.​org
License	Proprietary	AGPLv3
Design
Database model	Relational, Distributed data structure	Document-oriented, Schema-less, NoSQL
Data storage	Volatile memory, File System	Volatile memory, File System
Embeddable	Yes	Yes
Features
Query language	SQL	API calls, JavaScript, REST
Data types	All MySQL, JSON, BLOB	JSON
Conditional entry updates	Yes	Yes
Map and reduce	Yes	Yes
Unicode	Yes	Yes
TTL for entries	No	Yes
Compression	Yes	Yes
Integrity
Integrity model	ACID, MVCC	BASE
Atomicity	Yes	Conditional
Consistency	Yes	Yes
Isolation	Yes	Yes
Durability (data storage)	Yes	Yes
Transactions	Yes	No
Referential integrity	Yes	No
Revision control	Yes	No
Locking model	Lock Free Model, MVCC	Optimistic Locking, Lock on write
Indexing
Secondary Indexes	Yes	Yes
Composite keys	Yes	Yes
Full text search	No	Yes
Geospatial Indexes	Yes	Yes
Graph support	No	No
Graph type	Oriented graph	?
Distribution
Horizontal scalable	Yes	Yes
Replication	Yes	Yes
Replication mode	Master-Slave Replication	Master-Slave-Replica Replication
Sharding	Yes	Yes
Shared nothing architecture	Yes	Yes
Restrictions
Value size max.	1 000 EB	16 MB
System requirements
Operating system	Linux, Amazon EC2	Linux, Windows, Mac OS X
Native driver	C, C++, php, Java, Python, Objective-C, Ruby, Go	Java, php, Ruby, C#, Python, JavaScript, Haskell, Perl, C++, Erlang, Scala, C, Go
Memory recommended	8 GB	?
Memory minimum	8 GB	?
Architecture
Programming language	C++	C++
More
Description	In-Memory Database used for real-time analytics.	Document Oriented Database
Multi-user system	Yes	Yes
Accelerometer sensor	No	?
Price rating	●●●○○	●●●●●
Software distribution	Package management system	Tarball, Ubuntu Software Center, Package management system, Windows Installer
Object-Relational Mapping (ORM)	Yes	Yes
Release Date	18ᵗʰ June 2012	March 2009
Documentation level	●●●●○	●●●●●
Distributed Counter	Yes	?
Free to use	Yes	Yes
Active	Yes	Yes
Database Connection Pooling	Yes	Yes
Real time analytics	Yes	Yes
2 Letter Country Code	US	?
Cloud platform support	Amazon EC2	Heroku, CloudBee, Bluemix, Amazon EC2, SoftLayer
Online backup	Yes	Yes
Function Based Index	Yes	No
Log	Yes	Yes
Download	www.​memsql.​com/​#download	mongodb.​org/​downloads
Backup functionality	Good	Good
Query Cache	Yes	Yes
Ease of use	●●●●○	●●●●●
Free for commercial use	No	Yes
Sorts	Yes	Yes
Perfomance	●●●●○	●●●●○
Materialized Views	No	No
Spring Data Support	Yes	Yes
JSON	Yes	Yes
Stored Procedure	No	Yes
Concurrency	Yes	?
Multi-statement Transactions	Yes	Yes
Columner	Yes	?
Brand	?	MongoDB Inc
Extension/Plug-in	?	Yes
Database	?	MongoDB
Standard compliance	?	No
RESTful	?	Conditional
Lines of code	?	617 k
Community Driven	?	Good
Web interface	?	Yes
Data encryption	?	Conditional
Admin Generator	?	Yes
Partial Index	?	No
Key length max	?	128
Implementation flexibility	(0% global votes)	(48% global votes)
In-Place Update	?	Yes
Capped Collections	?	Yes
Tuneable write concerns	?	Yes
Read preferences	?	Yes
Open Source	?	Yes
Op/s	?	5 000
Triggers	?	No
Pause Test	?	Yes
Cross Domain Testing	?	No
Pipeline Aggregation	?	Yes
Geospatial	?	Yes
Server Side Java Script	?	Yes
Flexible Table(Schema)	?	Yes
Geo-distributed	?	Yes
Max rows in query result	?	1 000
Re-Reduce	?	Yes
Clustering over WAN	?	Yes
Fully Distributed	?	Yes
Auto-Sharding	?	Yes
memcached protocol	?	No
Monitoring UI	?	Yes
Recursive queries	?	No
Network datatype	?	No
Windowed aggregate	?	No
CLI`	?	Yes

This table is based on the vsChart comparison MemSQL vs. MongoDB comparison | vsChart.com, which is released under the Creative Commons Attribution-Share-Alike License 3.0.

wget and curl 指令

wget 指令介紹
curl 指令介紹
使用curl 批次下載

Linux 圖片轉檔指令

convert beach.gif beach.pnm


NAME
convert - convert an image or sequence of images

SYNOPSIS
convert [ options ... ] input_file output_file

DESCRIPTION
Convert converts an input file using one image format to an output file with a differing image format. In addition, various types of image processing can be performed on the converted image during the conversion process. Convert recognizes the image formats listed in ImageMagick.

Install Flask on CentOS 7.0

1. Install pip on CentOS 7.0

## First install the EPEL repo as per your Operating system version and architecture.
rpm -ivh http://mirror01.idc.hinet.net/EPEL/7/x86_64/e/epel-release-7-1.noarch.rpm
yum install -y python-pip

2. Install Flask

pip install Flask

## Test
vi hello.py

from flask import Flaskapp = Flask(__name__)
@app.route("/")def hello():    return "Hello World!"
if __name__ == "__main__":    app.run()

## Verify
python hello.py

* Running on http://0.0.0.0:80/

Python: ConfigParser

[core]
cmd = /usr/bin/vim

[mod]
safe_edit = yes
time_interval = 20

python 程式如下：

#!/usr/bin/python
from ConfigParser import SafeConfigParser
parser = SafeConfigParser()
parser.read('test.conf')

#傳回字串 /usr/bin/vim
parser.get('core', 'cmd')

#傳回 boolean 值 True
parser.getboolean('mod', 'safe_edit')

#傳回整數值 20
parser.getint('mod', 'time_interval')

references:
http://williewu.blogspot.tw/2007/10/python-configparser.html
https://wiki.python.org/moin/ConfigParserExamples
https://docs.python.org/2.6/library/configparser.html

How to find script's directory

import os
print os.path.dirname(os.path.realpath(__file__))

reference:
http://stackoverflow.com/questions/4934806/python-how-to-find-scripts-directory

strip in C programming

strtok(Name, "\n");

references:
http://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input

HPL 相關

How to calculate peak theoretical performance of a CPU-based HPC system

FLOPS per cycle for sandy-bridge and haswell SSE2/AVX/AVX2

System Performance and Ranking Estimation

http://hpl-calculator.sourceforge.net/HPL-HowTo.pdf

Linux TOP 指令說明

Linux TOP 指令說明

VIRT  程序使用的虛擬記憶體總量，單位 kb。VIRT=SWAP+RES

RES    程序使用的、未交換出的實體記憶體大小，單位 kb。RES=CODE+DATA

SHR    共享記憶體大小，單位 kb

reference

http://blog.ycnets.com/2013/09/01/linux-commandtop/

GnuPlot references

地圖/統計圖/3d 函數圖/實驗報告圖 -- Gnuplot 純畫圖 (作者: 洪朝貴老師)
http://user.frdm.info/ckhung/b/ma/gnuplot.php

Gnuplot 入門教學
http://randle.wordpress.com/2007/06/12/gnuplot-induction/

Upgrade to CentOS 6.5 from CentOS 6.4

yum clean all
yum update glibc* yum* rpm* python*
yum update

reboot

cat /etc/redhat-release
## Output ##
CentOS release 6.5 (Final)

lsb_release -a
## Output ##
LSB Version:    :base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID: CentOS
Description:    CentOS release 6.5 (Final)
Release:        6.5
Codename:       Final


references:
http://www.if-not-true-then-false.com/2011/upgrade-centos-6/

GDB: Missing separate debuginfos

Fixed GDB: Missing separate debuginfos

1. 修改 /etc/yum.repos.d/CentOS-Debuginfo.repo, set enabled=1
2. yum install yum-utils
3. debuginfo-install glibc

如果還是不行更新 gdb and glibc

yum install gdb* glibc*

參考:

http://stackoverflow.com/questions/10389988/missing-separate-debuginfos-use-debuginfo-install-glibc-2-12-1-47-el6-2-9-i686

Translate int to string

#include <iostream>
#include <string>
#include <sstream>

using namespace std;
string int2str(int &);
int main(void) {
  int i = 123;
  string s;
  s = int2str(i);

  cout << s << endl;
}

string int2str(int &i) {
  string s;
  stringstream ss(s);
  ss << i;

  return ss.str();
}

判斷奇偶數

利用位元運算來判斷奇偶數

if( (value & 1) == 0 )
  cout << "偶數";
else
  cout << "奇數";

數學符號表

http://zh.wikipedia.org/wiki/%E6%95%B0%E5%AD%A6%E7%AC%A6%E5%8F%B7%E8%A1%A8

C/C++ 中的括號

在 C語言中的括號分別化表

{ } 大括號表示函式本體的開始與結束
( ) 小括號在函式的宣告中使用

大括號的另類用法，指定了變數的作用範圍，在大括號中的變數都是局部變數，有效區域只在大括號中有效。有效利用這個特性可以使程式簡單明白。


 int a = 5;
  {
    int a = 2;
    printf("Here a=%d!!\n", a);
  }
  printf(" a=%d!!\n", a);

NFSv4 設定

最近在設定CentOS 6 的時候發現, NFS default 是用version 4. 不察之下發現設不起來 ><
底下是NFSv4 的設定

CentOS 6時，由於NFS為NFSv4，需多設定一個檔案為/etc/idmapd.conf 還有必須啟動rpcidmapd服務

Head Node

####  vi /etc/idmapd.conf
[General]
Verbosity = 1 #主要更改
# The following should be set to the local NFSv4 domain name
# The default is the host's DNS domain name.
Domain = snowfox #主要更改
.
. (略)
.
#Local-Realms =
[Mapping]
#Nobody-User = nobody
#Nobody-Group = nobody

然後 將rpcidmapd服務開啟 service rpcidmapd start chkconfig rpcidmapd --level 345 on

安裝 wxPython

[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://apt.sw.be/redhat/el$releasever/en/$basearch/dag
gpgcheck=1
enabled=1


yum install wxPython.x86_64 wxPython-devel.x86_64

Dependencies Resolved

==================================================================================================================================================
 Package                                Arch                           Version                                  Repository                   Size
==================================================================================================================================================
Installing:
 wxPython                               x86_64                         2.8.9.1-1.el5.rf                         dag                          22 M
 wxPython-devel                         x86_64                         2.8.9.1-1.el5.rf                         dag                         479 k
Installing for dependencies:
 wxGTK                                  x86_64                         2.8.10-1.el5.rf                          dag                          27 M
 wxGTK-devel                            x86_64                         2.8.10-1.el5.rf                          dag                         1.1 M

Identify the speed of memory

dmidecode  is a tool for dumping a computer’s DMI (some say SMBIOS) table contents in a human-readable format.


dmidecode

# dmidecode 2.11
SMBIOS 2.5 present.
30 structures occupying 1372 bytes.
Table at 0x0009D800.

vm.swappiness

vm.swappiness is a tunable kernel parameter that controls how much the kernel favors swap over RAM. At the source code level, it’s also defined as the tendency to steal mapped memory. A high swappiness value means that the kernel will be more apt to unmap mapped pages. A low swappiness value means the opposite, the kernel will be less apt to unmap mapped pages. In other words, the higher the vm.swappiness value, the more the system will swap.

The default value I’ve seen on both enterprise level Red Hat and SLES servers is 60.

step of modify:

sysctl -w vm.swappiness=0 (default: 60)

swapoff -a

swapon -a

ADD  vm.swappiness=0  to  /etc/sysctl.conf

References:
What Is the Linux Kernel Parameter vm.swappiness?
http://overinfinityresearch.blogspot.com/2008/09/ubuntu804.html