sra levels

level is enabled, each time the row is updated, the SQL Server database engine stores a copy of the original row in tempdb and adds the transaction sequence number to the row. Snapshots and MVCC At present, most relational databases use 2PL protocol to ensure the serialization of concurrent transaction execution, which creates the problem of read-write mutex, that is, s lock and X-lock mutex. The multi-version concurrency control (multi-version Concurrency CONTROL,MVCC) solves this problem b

read and will not lock the read to the row3. When the transaction isolation level is read Committed, the write data will only lock the corresponding row4, when the transaction isolation level is repeatable read, if there is an index (including the primary key index), the index as a condition to update the data, there will be a gap lock gap lock, Row lock, the next key lock problem, thereby locking some rows, if there is no index, the update data will lock the entire table. 5. When the transacti

additional hidden values are added after each row of data to implement MVCC, which is a record of when this row of data is created and another record of the rowWhen the data expires (or is deleted) in the actual operation, the storage is not the time, but the version number of the transaction, each opening a new transaction, the version number of the transaction will beIncreasing. Under the REPEATABLE READ Transaction ISOLATION level:Select, read create version number is not greater than curren

repeatable read and will not lock the read to the row3. When the transaction isolation level is read Committed, the write data will only lock the corresponding row4, when the transaction isolation level is repeatable read, if there is an index (including the primary key index), the index as a condition to update the data, there will be a gap lock gap lock, Row lock, the next key lock problem, thereby locking some rows, if there is no index, the update data will lock the entire table. 5. When th

Tags: SQL DCL Create user authorization View permissionsDCL1. Create a user* CREATE user username @ip address identified by ' password ';> users can only log on to the specified IP address* CREATE user username @ '% ' identified by ' password ';> Users can log on at any IP address2. Authorization to the user* GRANT permissions 1, ..., Permissions n on database. * To user name @ip address> Assign the user the specified permissions on the specified database> For example, Grantcreate,alter,drop,ins

1 uncommitted read (READ UNCOMMITTED): Dirty data will appear because the table is not locked.2 Commit read (Read Committed): 1. Update in transaction 1 locks the table and can select to the latest data.Transaction 2select cannot find the data. Will always wait. Plus with (NOLOCK) you can read it.2.select is an unlocked table, so other transactions can modify the data. When there are two select,The second select will show dirty data. cannot be read repeatedly.3 REPEATABLE READ (REPEATABLE Read):

How to check the database schema version, patch levels, and general monitoring readiness for patches in SharePoint Central Administration: Make sure that you are a farm administrator with access to central administration. Start: 1. Open Central Administration-upgrade and migration. 2. Click "View product and patch installation status". 3. A drop-down list at the top allows you to choose whether to view the entire farm or just the parts on a particular

Tags: x11 body div State full graphics into Inux Linux systemThe Linux system has 7 runlevel (runlevel): RunLevel 0: System down state, system default RunLevel cannot be set to 0, otherwise it will not start normally RunLevel 1: Single User working status, root privilege, for system maintenance, remote login Forbidden RunLevel 2: Multi-User State (no NFS) RunLevel 3: Full multiuser State (with NFS), enter console command line mode after login Run Level 4: System not used, reser

|+------+------+3 Rows in Set (0.00 sec) B> commit;Query OK, 0 rows affected (0.01 sec) The modification of a here should be num=3, but because of the Phantom reading, the thing B is submitted, but the thing a reads the old record,Like Phantom, when thing a changes, it finds that the result is 30, not the desired result 3a> Update test set num=num*3 where id=1;Query OK, 1 row affected (0.03 sec)Rows matched:1 changed:1 warnings:0 A> select * from test;+------+------+| ID | num |+------+------+|

Depressed, the attack power is so strong, but in group P, the king of 10 levels of Hill is always first suspended. This is the case many times! The output battle logs are as follows: [Hero name: Mountain King, lifecycle: 500, basic defense: 2][Hero name: priestess of the Moon, life value: 500, basic defense: 1][Hero name: King of 10 levels of Hill, life value: 500, basic defense: 1]The battle begins ......1

The company is facing rare development opportunities and human resource management challenges brought about by rapid team expansion, international operation, and cross-cultural management. The responsibility of a leader is to "arrange, dispatch, and accompany customers to dinner ". "Deployment" refers to the Construction of organizational units and organizational activities; "dianbing" refers to the implementation of the cadre selection, use, and assessment routes and the harmonious solution of

Many network administrators working on Cisco IOS have never bothered to consider the level of permissions they are using or the meaning of these levels. However, Cisco IOS actually has sixteen different permission levels. David Davis discusses these different levels and describes the main commands needed to configure these permissions.Do you know why Cisco IOS pr

In fact, an organization that we can think of is composed of a number of columns of information processing activities, as the organization expands and grows, information processing and control becomes more and more difficult, so we need to manage and monitor information security. According to the Faculty of Computer Science at Duke University and the University of Sydney, all organizations can be viewed and managed from a three-level system, so we can manage and control information security issu

Detailed description of four transaction isolation levels of MySQL The SQL standard defines four isolation levels, including some specific rules to limit which changes inside and outside the transaction are visible and which are invisible. Low-level Isolation generally supports higher concurrent processing and lower system overhead. Detailed description of four transaction isolation

state to another. Therefore, when the database contains only the results of successful transaction commits, the database is said to be in a consistent state. If a database system fails in operation and some transactions have not yet been completed, some of the modifications made to the database have been written to the physical database, and the database is in an incorrect state, or an inconsistent state. 3, isolation. Execution of one transaction cannot interfere with other transactions. That

in the above example, the database is consistent on the data before and after the transfer. Isolation: If multiple transactions are executed concurrently, the result should be the same as the serial execution of multiple transactions. Obviously, the simplest isolation is the serial execution of all the transactions: first, First, and one to allow the next to execute. However, the database is inefficient, such as: Two different transactions just read the same batch of data, so it can be done con

Detailed description and comparison of the four transaction isolation levels of MySQL, and detailed description of mysql Detailed description and comparison of the four transaction isolation levels of MySQL At the SQL: 1992 transaction isolation level, InnoDB is REPEATABLE READ by default ). MySQL/InnoDB provides all four transaction isolation levels described in

exactly what they are and what they are connected to.What is a "cascading context"cascading contexts (stacking context) is a three-dimensional concept in HTML. In the CSS2.1 specification, the position of each box model is three-dimensional, which is on a flat canvas and X轴 Y轴 represents a cascade Z轴 . In general, elements areOn the page along the X轴Y轴 tile, we don't notice the Z轴 cascading relationships on top of them. Once the element is stacked, it can be found that an element might overwrit

)Isolation is when multiple users concurrently access the database, such as when the same table operation, the database for each user-opened transactions, can not be disturbed by the operation of other transactions, multiple concurrent transactions to be isolated from each other. To achieve this effect: for any two concurrent transactions T1 and T2, in the case of transaction T1, the T2 either ends before the T1 starts, or starts after the T1 ends, so that every transaction does not feel that an

speak.Isolation (Isolation): In general, changes made by an office are not visible to other transactions until they are finally submitted. Notice here that the "usual", behind the transaction isolation level will be said.Durability (persistent): Once a transaction commits, its modifications are persisted to the database. When the system crashes, the modified data is not lost. (There is also a relationship between persistent security and the refresh log level, which corresponds to different