Tags: count set InnoDB Department CTI hard disk redo log independently completedThere are four transaction isolation levels for Mysqlinnodb: ( default is repeatable read REPEATABLE read) UNCOMMITTED Read Uncommit : The data was modified in another transaction but not yet committed, and in this transaction the SELECT statement may query for these uncommitted data
1. Physics reading (physical read)
When the data block is first read, it will be cached in the buffer cache, while the second read and modify the data block in memory buffer cache The following is an example:
1.1 First read:
C:\Documents and Settings\paul yi>sqlplus "/as sysdba"
Sql*plus:release 9.2.0.4.0-production on
Read behavior is a condition that can be encountered when multiple transactions are executing concurrently, while reading data. Understanding them first helps you understand the meaning of each isolation level. These include dirty reads, non-repeatable reads, and Phantom reads.Dirty read:Dirty read also known as invalid data readout, refers to in the database access, transaction T1 a value modification, and
Isolation level of a database transactionThere 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. 1. 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
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
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) 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
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 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,
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
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
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
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 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,
Read all names from text files similar to the following, print duplicate names and repea
———————————————————————————————————————————Read and write a string from a file (read/write directly/through Nsurl)#import int main (int argc, const char * argv[]) {@autoreleasepool {Writes a string directly to a file ***************NSString *str1=[[nsstring Alloc]init];[Email protected] "Lalalalala";Not through Nsurl, and directly to the string str1 write to an address file, as long as the creation of the c
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