2022年5月25日星期三

Slow MySql Server Performance - What and How to check?

Posted on 上午9:52 by 亞爾文俊

Slow MySql Server Performance - What and How to check?

Log slow queries- If your system has a ton of queries, it gets tougher to find out which queries are slowing your system. MySQL provides a tool to log slow queries for further analysis https://dev.mysql.com/doc/refman/8.0/en/slow-query-log.html

EXPLAIN Extended command shows details about your queries when your have no idea what is happening https://dev.mysql.com/doc/refman/8.0/en/explain-extended.html

To speed up your queries use Index - A good practice is add index by seeing which fields are in the WHERE clause add index for them. Also if you are retrieving all fields from a table, the query gets slower by fetching all data from disk. In SELECT query you should specify which fields you need to bring instead to bring them all with *

Not

SELECT * FORM xTable ;

Yes

SELECT ID, Name, Addr FORM xTable ;

Make use of Query Cache https://dev.mysql.com/doc/refman/5.7/en/query-cache-configuration.html

SHOW VARIABLES LIKE 'have_query_cache';

Make sure that your MySQL server configuration file options are optimized according to your hardware https://dev.mysql.com/doc/refman/8.0/en/option-files.html

Make sure that you are using optimized data types while creating a table structure For example "Comments" fields has size of 256 characters, reply it to MYSQL with a field with type VARCHAR(256) instead of using TEXT. The query will be much faster.

rocedure_Analyse() can help you in finding optimal data types:

http://www.mysqlperformanceblog.com/2009/03/23/procedure-analyse/

http://dev.mysql.com/doc/refman/5.0/en/procedure-analyse.html

http://dba.stackexchange.com/questions/53229/slow-mysql-server-performance-what-and-how-to-check

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2022年5月20日星期五

正則表達式 (regex) 各程式語言使用方法 (part 5)

Posted on 下午5:17 by 亞爾文俊

#Java

public class RegexTestStrings {
  public static final String EXAMPLE_TEST = "This is my small example "
      + "string which I'm going to " + "use for pattern matching.";

  public static void main(String[] args) {
    System.out.println(EXAMPLE_TEST.matches("\\w.*"));
    String[] splitString = (EXAMPLE_TEST.split("\\s+"));
    System.out.println(splitString.length);// should be 14
    for (String string : splitString) {
      System.out.println(string);
    }
    // replace all whitespace with tabs
    System.out.println(EXAMPLE_TEST.replaceAll("\\s+", "\t"));
  }
}

#PHP

$str = 'a1234';
if (preg_match("/^[a-zA-Z0-9]{4,16}$/", $str)) {
    echo "驗證成功";
} else {
    echo "驗證失敗";
}

#perl 
print $str = "a1234" =~ m:^[a-zA-Z0-9]{4,16}$: ? "COMFIRM" : "FAILED";

正則表達式 (regex) 簡介 (part 1)
正則表達式 (regex) 簡介 (part 2)
正則表達式 (regex) 簡介 (part 3)
正則表達式 (regex) 簡介 (part 4)
正則表達式 (regex) 簡介 (part 5)

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A newspaper (often just called a paper when the context is clear) is a periodical publication containing news, other informative articles (listed below), and usually advertising. A newspaper is usually printed on relatively inexpensive, low-grade paper such as newsprint. The news organizations that publish newspapers are themselves often metonymically called newspapers. Most newspapers now publish online as well as in print. The online versions are called online newspapers or news sites. 60666066

Name : Chan Tai Man
Tel: 24882488 , 2499 2499 , 139 6888 6888
Email : abc@gmail.com, def@yahoo.com
HKID: A123456(7) , A123456(A)
TWID: A168145309
Website : www.google.com
Time: 00:00:00

HKID
\w\d{6}[\(][\daA]\)

Time (hh:mm:ss)
\d{2}\:\d{2}\:\d{2}

Ref: http://myregexp.com/

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只能輸入1個數字
表達式	\d$
描述	匹配一個數字
匹配的例子	0,1,2,3
不匹配的例子

只能輸入n個數字
表達式	\d{8}
描述	匹配8個數字
匹配的例子	12345678,22223334,12344321
不匹配的例子

只能輸入至少n個數字
表達式	\d{8,}
描述	匹配最少n個數字
匹配的例子	12345678,123456789,12344321
不匹配的例子

只能輸入m到n個數字
表達式	\d{7,8}$
描述	匹配m到n個數字
匹配的例子	12345678,1234567
不匹配的例子	123456,123456789

只能輸入數字
表達式	[0-9]*$
描述	匹配任意個數字
匹配的例子	12345678,1234567
不匹配的例子	E,

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2022年5月25日星期三