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Dirty read Phantom read non-repeatable read

1, Dirty ReadA transaction is read to another transaction, and a modification that has not yet been committed is a dirty read. Here are the so-called modifications, in addition to the update operation, do not forget that also includesInsert and delete operations.The consequences of dirty reads: If the latter transaction is rolled back, all of its modifications will be revoked. The data that the previous tra

Database dirty read, non-repeatable read, Phantom read

Label:Article Source: http://www.bkjia.com/sjkjc/806530.html The database's dirty reads, non-repeatable reads, and Phantom reads are all related to the isolation of the transaction. So first look at the 4 major features of the transaction.4 Characteristics of the transaction (ACID): Atomicity (atomicity): A transaction is a logical unit of work for a database, and its modifications to the database are either all executed or not executed at all. Consistency (CONSISTEMCY): Before and

Buffer Cache Experiment 9: Read data block parsing from buffer Caceh-read from logical to physical read

Let's start with a big picture: SQL statement used: bys@ ocm1>select dbms_rowid.rowid_relative_fno (ROWID) file#,dbms_rowid.rowid_block_number rowid (Block#,deptno) From Bys.test; file# block# DEPTNO ---------- ---------- ---------- 4 391 10 As an example of the above diagram, the text description analyzes the process of obtaining the required data blocks when the foreground process issues a query statement: Note: This article does not involve the parsing part of SQL statements, client

Summary of C ++ read/write file instances (stringtoken is read in units and char is read in units)

1. Read all strings separated by spaces in the specified file. # Include Ifstream indata; // For the file Indata. Clear (); String filename;Filename = "primes.txt "; Indata. Open (filename. c_str ());String temp_word; // You can also directly read the integer data int temp_word here;// Indata> temp_word; While (indata. EOF ()) // If the file contains a line break, you need to use while (indata. Good ()

Set global read_only=0; Turn off read-only, you can read and write set global read_only=1; Start Read Only mode

mysql> set global read_only=0; Query OK, 0 rows Affected (0.00 sec) mysql> show variables like '%read_only% '; +------------------+-------+ | Variable_name | Value | +------------------+-------+ | innodb_read_only | Off | | read_only | Off | | tx_read_only | Off | +------------------+-------+ 3 rows in Set (0.00 sec) mysql> set global read_only=1; Query OK, 0 rows Affected (0.00 sec) mysql> show variables like '%read_only% '; +------------------+-------+ | Variable_name

MySQLInnoDB has four transaction levels: Dirty read, no repeated read, and phantom read.

MySQL InnoDB Transaction isolation level dirty read, Repeatable read, phantom read MySQL InnoDB transactions are isolated at four levels. The default value is repeatable read ). · READUNCOMMITTED ). Another transaction modifies the data but has not yet committed it, And the SELECT statement in this transaction reads th

Day eighth read, write, append, read/write, read, Seek () move the cursor, modify the file, and another way to open the file

  Main content:1. Initial file operation2. Read-only (R,RB)3. Write only (W,WB)4. Append (A, AB)5. Read and write (r+)6. Write-read (w+)7. Additional write read (A +)8. Other methods of operation9. File modification and another way to open a file handleA. Operation of the initial fileusing Python to

Database transaction ISOLATION LEVEL-dirty read, Phantom Read, non-repeatable read

I. DATABASE TRANSACTION ISOLATION LEVELThere are 4 isolation levels for database transactions, from low to high, READ UNCOMMITTED,Read Committed,Repeatable read, andSerializable, which can be resolved individually by each of the four levels Problems such as dirty reading, non-repetition reading, and Phantom reading. √: May appear x: does not appear

Dirty read (dirty read) unrepeatable read (phantom problem) Parsing

Dirty read (dirty read) unrepeatable read (phantom problem) Parsing1. Dirty read First, distinguish between dirty pages and dirty data Dirty pages are modified pages in the memory buffer pool. They are not flushed to the hard disk in time, but are already written to the redo log. It is normal to

SQL Server logical read, pre-read, and physical read

Label:form of SQL Server data store Pre-read: Use the estimated information to go to the hard disk to read the data to the cache. Pre-read 100 times, which is estimated to read 100 pages of data from the hard disk to the cache. Physical reads: After the query plan is generated, if the cache is missing the

SQL Server logical read-pre-read-physical read

SQL Server logical read-pre-read-physical readHow SQL Server stores data 1. The page is the smallest operating unit, that is, read the database from disk at least one page, each page size is 8kb,sql server read to the page is atomic, either read a page, or completely unread,

Dirty read, non-repeated read, phantom read Comprehension

1. Dirty read: Dirty read means that when a transaction is accessing data and modifying the data has not been committed to the database, another transaction also accesses the data, then the data is used. 2. Repeated read is not allowed.: Refers to reading the same data multiple times in a transaction. When the transaction is not completed, another transaction als

C ++ I/O Stream class library (3): file read/write, binary file read/write, random file read/write

I. file read/write As mentioned above, stream reads and writes mainly include C ++ code 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 # Include # Include #

A detailed explanation of the database problem (dirty read, non-repeatable read, Phantom Read)

One, dirty reading, non-repeatable reading, Phantom reading 1, dirty read: Dirty read refers to when a transaction is accessing the data, and the data has been modified, and this modification has not been committed to the database, then another transaction also accesses the data, and then used this data.For example:Zhang San's salary was 5000 and transaction a changed his salary to 8000, but transaction a

Android TXT file read/write (read resource file, read private and SD file method)

Import Java.io.FileInputStream; Import Java.io.FileOutputStream; Import Java.io.InputStream; Import Org.apache.http.util.EncodingUtils; Import android.app.Activity; public class FileAccess {/** *, file access under Private folder (/data/data/package name/files) * * @param fileName * @param mess Age */public void Writefiledata (string fileName, String message) {try {FileOutputStream fou t = openfileoutput (fileName, mode_private); byte[] bytes = Message.getbytes ();

Comparison of VaR read/write and function read/write, get/set read/write Efficiency

Comparison of VaR read/write and function read/write, get/set read/write Efficiency VaR is about 4 times faster than function, GET/set is similar to function 95VaR read: 567VaR write: 563[SWF] D: \ flexproject \ testspeed \ bin-Debug \ testspeed.swf-2,091 bytes after decompressionFunction

SQL Server logical read, pre-read, and physical read

Tags: style class blog Code color data DBCC Dropcleanbuffers -- empty cache SETSTATISTICSon -- Turn on IO statistics SELECT* from person -- query statement     Pre-read: Use the estimated information to go to the hard disk to read the data to the cache. Pre-read 100 times, which is estimated to read 100

Read all ------------ one-time read of all. Read () vs a row of for Iteration

Read all F = open ("Xi Yang", mode = "r", encoding = "UTF-8 ") Method 1: Read all at onceF = open ("Xi Yang", mode = "r", encoding = "UTF-8 ") Print (F. Read ()) Method 2: Read data in one row (determine the quantity and use for in iteration) F = open ("Xi Yang", mode = "r", encoding = "UTF-8 ") For line in F

Java Algorithm interview questions: Read all names from text files similar to the following, print duplicate names and repeated times, and sort by repeated times; read docx and read doc. Use the poi jar package to provide download,

Java Algorithm interview questions: Read all names from text files similar to the following, print duplicate names and repeated times, and sort by repeated times; read docx and read doc. Use the poi jar package to provide download, Read all names from text files similar to the following, print duplicate names and repea

PHP read the source of the Web page, export to TXT file, read xls, read the file name of all files under the folder

Read Web page source code$curl = Curl_init ();curl_setopt ($curl, Curlopt_url, $url);curl_setopt ($curl, Curlopt_header, 1);curl_setopt ($curl, Curlopt_returntransfer, 1);curl_setopt ($curl, Curlopt_ssl_verifypeer, false);//This is the point.$contents = curl_exec ($curl);Export as TXT file$str = "ABCD";$FP =fopen ("Pic.txt", "w");Fputs ($fp, $STR);Fclose ($FP);Read tableRequire_once ' excel_reader2.php ';$d

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