Optimistic Offline Locking
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Overview Concurrency Optimistic Lock Entity Framework Optimistic Lock Aecho Penpower, Inc [email protected] 2013, 08 1 / 29
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討論關於Offline Locing的其中一種。Optimistic Offline Locking。Team內部教育訓練用。
Transcript of Optimistic Offline Locking
Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock
Aecho
Penpower, Inc
2013, 08
1 / 29
Overview Concurrency Optimistic Lock Entity Framework
Overview
Overview
Concurrency
Optimistic Lock
Entity Framework
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency
What is concurrency ???
.
......Several computations are executing simultaneously.
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency
What is concurrency ???
.
......Several computations are executing simultaneously.
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency ProblemsWhenever you have multiple processes, or threads manipulatingthe same data, you run into concurrency problems.
.
......Concurrency is hard to think about, and it’s difficult to enumeratepossible scenarios.
.
......Concurrency is hard to test for.
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency ProblemsWhenever you have multiple processes, or threads manipulatingthe same data, you run into concurrency problems.
.
......Concurrency is hard to think about, and it’s difficult to enumeratepossible scenarios.
.
......Concurrency is hard to test for.
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency ProblemsThe essential concurrency problems.
• Lost Updates• Inconsistent Reads
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Overview Concurrency Optimistic Lock Entity Framework
Lost Updates洋蔥.
......
get CustomerA ;
.
......
update CustomerA ;
九層塔
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get CustomerA ;
.
......
update CustomerA ;// 洋蔥 , l o s t update
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Overview Concurrency Optimistic Lock Entity Framework
Inconsistent Reads洋蔥.
......
get CustomerA ;
.
......
update CustomerA ;
九層塔
.
......
get CustomerA ;
.
......
// CustomerA , I n c o n s i s t e n t Reads// get CustomerA ;update CustomerA ;
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency Controls• Pessimistic Lock• Optimistic Lock
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Overview Concurrency Optimistic Lock Entity Framework
Pessimistic Lock
.
......Prevent conflicts between concurrent business transactions byallowing only one business transaction to access data at once.
.
......Conflict Prevention.
.
......Hard to implement.
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Overview Concurrency Optimistic Lock Entity Framework
Pessimistic Lock
.
......Prevent conflicts between concurrent business transactions byallowing only one business transaction to access data at once.
.
......Conflict Prevention.
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......Hard to implement.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock
.
......Prevent conflicts between concurrent business transactions, bydetecting a conflict and rolling back the transaction.
.
......Conflict Detection.
.
......Easy to implement.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock
.
......Prevent conflicts between concurrent business transactions, bydetecting a conflict and rolling back the transaction.
.
......Conflict Detection.
.
......Easy to implement.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock• Most common implementation
Each record associates with a version number.1
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......It checks the version number before executing update or deletesql command.
• Bad IdeaUse modification time-stamp rather than a version counter.
.
......System clocks are simply too unreliable. Even more so if you arecoordinating across multiple servers.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock• Most common implementation
Each record associates with a version number.1
.
......It checks the version number before executing update or deletesql command.
• Bad IdeaUse modification time-stamp rather than a version counter.
.
......System clocks are simply too unreliable. Even more so if you arecoordinating across multiple servers.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock• Most common implementation
Each record associates with a version number.1
.
......It checks the version number before executing update or deletesql command.
• Bad IdeaUse modification time-stamp rather than a version counter.
.
......System clocks are simply too unreliable. Even more so if you arecoordinating across multiple servers.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock• Most common implementation
Each record associates with a version number.1
.
......It checks the version number before executing update or deletesql command.
• Bad IdeaUse modification time-stamp rather than a version counter.
.
......System clocks are simply too unreliable. Even more so if you arecoordinating across multiple servers.
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock洋蔥.
......
get customerA ;
.
......
update customerA ;// ! Detect a c o n f l i c t .// ! Because the customerA has been
updated .
九層塔
.
......
get customerA ;. . .
update customerA ;
How about pessimistic lock ?
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Overview Concurrency Optimistic Lock Entity Framework
Optimistic Lock洋蔥.
......
get customerA ;
.
......
update customerA ;// ! Detect a c o n f l i c t .// ! Because the customerA has been
updated .
九層塔
.
......
get customerA ;. . .
update customerA ;
How about pessimistic lock ?
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency Problems.
......
Pessimistic OptimisticLost Update No NoInconsistent reads No Maybe
About Optimistic lock,• It cannot deal with inconsistent read problem.
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Overview Concurrency Optimistic Lock Entity Framework
Concurrency Problems.
......
Pessimistic OptimisticLost Update No NoInconsistent reads No Maybe
About Optimistic lock,• It cannot deal with inconsistent read problem.
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Overview Concurrency Optimistic Lock Entity Framework
Entity FrameworkThe MSSQL database server supports the optimistic lockingmechanism.
.
......MSSQL 2012, timestamp column type.
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Overview Concurrency Optimistic Lock Entity Framework
Entity FrameworkThe MSSQL database server supports the optimistic lockingmechanism.
.
......MSSQL 2012, timestamp column type.
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Overview Concurrency Optimistic Lock Entity Framework
Entity Framework.Code First..
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[ Table ( ”db_contact” ) ]pub l i c c l a s s Contact {
[ Key ]pub l i c Guid Guid { get ; s e t ; }
pub l i c DateTime CreatedTimeUTC { get ; s e t ; }pub l i c DateTime ModifiedTimeUTC { get ; s e t ; }
[ Timestamp ]pub l i c byte [ ] db_row_version { get ; s e t ; }
[ NotMapped ]pub l i c s t r i n g RowVersion {
// Convert db_row_version bytes to s t r i n g .get { . . . }// Convert s t r i n g to db_row_version bytes .s e t { . . . }
}}
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Overview Concurrency Optimistic Lock Entity Framework
Entity Framework.DDL Syntax..
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CREATE TABLE [ dbo ] . [ ContactSet ] ([ Guid ] u n i q u e i d e n t i f i e r NOT NULL,[ CreatedTimeUTC ] datet ime NOT NULL,[ ExpiredTimeUTC ] datet ime NOT NULL,[ db_row_version ] rowvers ion NOT NULL,
) ;GO
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Overview Concurrency Optimistic Lock Entity Framework
Entity FrameworkThe timestamp column type in DDL is deprecated..timestamp column type..
......
CREATE TABLE ExampleTable2 ( PriKey i n t PRIMARY KEY, VerCol timestamp ) ;
.rowversion column type..
......
CREATE TABLE ExampleTable2 ( PriKey i n t PRIMARY KEY, VerCol rowvers ion ) ;
.NOTE..
......The column type will be timestamp.
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Overview Concurrency Optimistic Lock Entity Framework
Entity FrameworkThe timestamp column type in DDL is deprecated..timestamp column type..
......
CREATE TABLE ExampleTable2 ( PriKey i n t PRIMARY KEY, VerCol timestamp ) ;
.rowversion column type..
......
CREATE TABLE ExampleTable2 ( PriKey i n t PRIMARY KEY, VerCol rowvers ion ) ;
.NOTE..
......The column type will be timestamp.
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Overview Concurrency Optimistic Lock Entity Framework
The End
Any questions ?
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