wcag levels

then T1 performs the rollback operation, canceling the modification that was just made. Now the line read by T2 is invalid. ) exp: Xiaoming's score was 89, and transaction a changed his score to 98, but transaction A was not yet committed. at the same time, transaction B is reading Xiaoming's score, reading to Xiaoming's score is 98. then, transaction A to the exception and rolled back the transaction. Xiaoming's score rolled back to 89. finally, transaction B reads the data for Xiaoming wi

There are four database isolation levels, as described in the "high-performance MySQL" Book:Then talk about how to modify the transaction isolation level:1. Global modification, modify the Mysql.ini configuration file, at last add1 #可选参数有: read-uncommitted, read-committed, Repeatable-read, serializable.2 [mysqld]3 transaction-isolation = Repeatable-readHere the global default is Repeatable-read, in fact, MySQL is the default is this level2. Modify the

Read uncommited (UNCOMMITTED)At the Rerad uncommited level, modifications in a transaction are visible to other transactions, even if they are not committed. The transaction can read uncommitted data, which also becomes dirty read (Dirty read). This level can cause a lot of problems, in terms of performance, read uncommited will not be much better than the other levels, but there is a lack of other levels o

space being inserted into the qlineedit.If the target control is not qlineedit, or the key is not a spacebar, we will pass the event to the EventFilter () function of the base class.QT provides 5 levels of event processing and filtering:1, re-implement the event function. For example: Mousepressevent (), Keypress-event (), PaintEvent ().This is the most common method of event handling.2, re-implement Qobject::event ().This is typically used when QT d

To develop an application, the importance of logging is self-evident. However, it is sometimes found that a large number of garbage logs appear in the log. The so-called spam logs are logs that you do not need to know, or the logs are not useful for viewing or tracking apps. It is also (but not only) that the common log framework sets the log level for these issues. But when writing a program, which of these log levels to choose, does not have a unifo

lock for INSERT, UPDATE, delete is also releasedAlthough deadlock cannot be avoided in this way, the two-segment locking protocol ensures that concurrent scheduling of transactions is serialized (serialization is important, especially when data recovery and backup). Lock mode in a transactionFour isolation levels for transactionsin the database operation, the transaction isolation level is proposed in order to effectively guarantee the correctness o

2 transaction isolation levels supported by Oracle Read committed and Serializable The Read committed is the default isolation level. Isolation levels (Isolation level) The isolation level defines the degree of isolation between transactions and transactions. The isolation level and concurrency are contradictory: the higher the degree of isolation, the worse the concurrency of the database, and the lower

Tags: mysql four kinds of transaction isolation mechanismThe MySQL standard defines 4 isolation levels that define which changes within and outside a transaction are visible and which are not.Low isolation levels generally support higher concurrency and lower system overhead.Isolation levels from low to High: READ UNCOMMITTED First: READ UNCOMMITTED (read UNCOMMI

Article Source: http://blog.chinaunix.net/uid-22746363-id-383989.htmlLinux System has 7 runlevel (runlevel)RunLevel 0: System down state, system default RunLevel cannot be set to 0, otherwise it will not start normallyRunLevel 1: Single User working status, root privilege, for system maintenance, remote login ForbiddenRunLevel 2: Multi-User State (no NFS)RunLevel 3: Full multiuser State (with NFS), enter console command line mode after loginRun Level 4: System not used, reservedRun level 5:x11 c

RAID It means a redundant array of inexpensive disks (redundant array of inexpensive Disks), but now it is known as a redundant array of independent disks (redundant array of independent Drives). Earlier a very small disk was very expensive, but now we can buy a larger disk cheaply. Raid is a collection of disks that are put together to become a logical volume. AID contains a group or a collection or even an array. Use a set of disk-combined drives to compose a RAID array or RAID set. Connect at

transactions that read data do not prevent other transactions from writing to the data. transactions that write data do not prevent SNAPSHOT transactions from reading data. in the rollback phase of database recovery, if you attempt to read data that is locked by another transaction that is being rolled back, the SNAPSHOT transaction will request a lock. the SNAPSHOT transaction is blocked until the transaction has finished rolling back. when a transaction is authorized, the lock is released im

According to the parameter Display category (three levels of association, JSON data is required ), Scripts/Category. js Call method:$ (Function () {BindCategory (); // BindCategoryData ($ ("# txtCategoryId"). val () by default, BindCategory ());})View Code Binding three levels of linkage (see: http://www.cnblogs.com/haozhenjie819/p/3887279.html for details)Function BindCategory () {var $ txtCategory = $ ("#

Simple implementation of three levels of Ajax Product Classification Association (case study ), Train of Thought Analysis: Effect: When a page is loaded, ajax is used to asynchronously request data from the background to load the first-level commodity category. When the first-level commodity is selected, the second-level commodity is loaded and the second-level commodity is loaded. Implementation: 1. After obtaining the data, load the product with a p

point), for example:Assume that the following route matching rules are registered (the controller, the webapi of the action, and the character of the route) Config. Routes.maphttproute ( name: "Defaultareaapi", routetemplate: "Api/{area}/{controller}/{action}/{id}", defaults:new {id = routeparameter.optional} ); Config. Routes.maphttproute ( name: "Defaultapi", routetemplate: "Api/{control

Tags: HTTP Problem c html ef r management HTM TTIn an enterprise, listening is the basis for communication between managers and employees. However, in reality, many people do not really master the art of "listening. According to the analysis, there are different levels of listening.The lowest is "listen without hearing": As you have heard, you have never heard of it;The second is "perfunctory": Well ...... Oh ...... Good ...... Ah ...... A slight reac

In Android, citypickerview, an open-source framework, is used to achieve three levels of association between provinces, cities, and cities,1. Overview I remember that when I was working on a mall project, I needed to implement provincial/municipal linkages in the address selection to facilitate users to quickly enter the address. At that time, I used an open-source control called android-wheel, at that time, I felt very easy to use. The only trouble w

Test your understanding of MySQL transactions and isolation levels. I have written an article titled MySQL InnoDB Transaction isolation level and dirty read, Repeatable read, phantom read Http://blog.csdn.net/seven_3306/article/details/27085275 This is a question I have figured out about MySQL transaction and isolation level. Please fill in the question mark section: If you can correctly explain the following results, you should have a certain und

Ztree implements three levels of action Provinceaction. Java: /** * @Title:ProvinceAction.java * @Package:com.gwtjs.struts.action.area * @Description: * @author:Youhaidong(游海东) * @date:2014-5-11 上午12:27:54 * @version V1.0 */package com.gwtjs.struts.action.area;import java.util.List;import javax.annotation.Resource;import javax.xml.ws.Action;import org.apache.struts2.convention.annotation.Namespace;import org.apache.struts2.convention.annotati

For H.264 users, how to specify the profile/level seems to be a fairly common question.ProfilesDefine sets of bit stream features a H.264 stream can use.LevelsDefine restrictions on the video resolution, frame. Rate and some stuff called vbv (video buffer verifier ). H. 264 profiles H. 264 profiles are discussed in depth onwikipedia, But to simplify the considerations for the average user, I will focus on the baseline, main and high profiles. Baseline Profile I/P slices Multiple refer