Sofia, Bulgaria | 9-10 October Concurrency Management – ADO.NET 2.0 Presented By: Sahil Malik ...

Sofia, Bulgaria | 9-10 OctoberSofia, Bulgaria | 9-10 October

Concurrency Management – ADO.NET 2.0

Concurrency Management – ADO.NET 2.0

Presented By: Sahil Malik

http://www.winsmarts.com

Presented By: Sahil Malik

http://www.winsmarts.com

Sofia, Bulgaria | 9-10 October

About MeAbout Me

● Microsoft MVP (Visual C#), INETA speaker, telerik Technical Evangelist

● Author three books.

● Reviewer on several.

● Available for technical consulting or training for your organization.

● Contact me at www.winsmarts.com (that’s smart”S” with an “S”)

● Microsoft MVP (Visual C#), INETA speaker, telerik Technical Evangelist

● Author three books.

● Reviewer on several.

● Available for technical consulting or training for your organization.

● Contact me at www.winsmarts.com (that’s smart”S” with an “S”)


What is a concurrency conflict?What is a concurrency conflict?


Database ExampleDatabase Example

PersonID

Expenditure

1 $100.00

PersonID

Expenditure

1 $120.00PersonID

Expenditure

1 $120.00

Spend $20 - Twice


SolutionSolution

● Send in only the change – let the database do the addition?

● Good approach – but might not solve every situation.

● Send in only the change – let the database do the addition?

● Good approach – but might not solve every situation.


Concurrency ResolutionConcurrency Resolution

● Design the database right.

● Staging Area

● Journaling database

● Always unique primary keys

● Request a number of keys in advance

● Use GUIDs

● Use a Seed Generator Table

● This prevents conflicts, but does not eliminate them.

● Design the database right.

● Staging Area

● Journaling database

● Always unique primary keys

● Request a number of keys in advance

● Use GUIDs

● Use a Seed Generator Table

● This prevents conflicts, but does not eliminate them.


Conflict happens !!Conflict happens !!

● Pessimistic Locking

● Optimistic Concurrency Control

● Pessimistic Locking

● Optimistic Concurrency Control


Pessimistic LockingPessimistic Locking


Pessimistic Locking - DatabasePessimistic Locking - Database

Select

Finger

From

GirlFriends HOLDLOCK

Where

GirlfriendName = ‘Jane’

Select

Finger

From

GirlFriends HOLDLOCK

Where

GirlfriendName = ‘Jane’


Pessimistic Locking – ADO.NETPessimistic Locking – ADO.NET

● Isolation Level = RepeatableRead or

● Isolation Level = Serializable

● Or just execute the HOLDLOCK command.

● Isolation Level = RepeatableRead or

● Isolation Level = Serializable

● Or just execute the HOLDLOCK command.


Pessimistic Locking - AdvantagesPessimistic Locking - Advantages

● You can be sure nobody touched your record.

● Apparently simple programming model

● Intuitive approach – but don’t do it !!!

● SERIOUSLY !! DON’T DO IT !!

● But Why?

● You can be sure nobody touched your record.

● Apparently simple programming model

● Intuitive approach – but don’t do it !!!

● SERIOUSLY !! DON’T DO IT !!

● But Why?


Pessimistic Locking - DownsidesPessimistic Locking - Downsides

● The girl can’t date anybody else – nobody else can access that database row.

● Erick could have died in a war – the program user could have locked a row and left for lunch, who unlocks the row?

● Deadlocks

● A serious hit on performance.

● The girl can’t date anybody else – nobody else can access that database row.

● Erick could have died in a war – the program user could have locked a row and left for lunch, who unlocks the row?

● Deadlocks

● A serious hit on performance.


Pessimistic Locking - AlternativesPessimistic Locking - Alternatives

● If you must use pessimistic locking, instead try and use –

● Server side cursors. Position the cursor on the row you wish to update, and thus always work with the latest possible value.

● Create an IsLocked column, and have application logic read that column and act accordingly. Similar to checkin/checkout.● You are technically disconnected this way, but you

still have to worry about timeouts, and unexpected application crashes, but at least the performance is better.

● If you must use pessimistic locking, instead try and use –

● Server side cursors. Position the cursor on the row you wish to update, and thus always work with the latest possible value.

● Create an IsLocked column, and have application logic read that column and act accordingly. Similar to checkin/checkout.● You are technically disconnected this way, but you

still have to worry about timeouts, and unexpected application crashes, but at least the performance is better.


Optimistic ConcurrencyOptimistic Concurrency

● Various flavors of optimistic concurrency exist.

● Primary Keys a.k.a. Last In Wins !!

● Primary Keys + Changed Columns

● Primary Keys + All Columns

● Primary Keys + Timestamp/rowversion

● Show me some code man !!

● Various flavors of optimistic concurrency exist.

● Primary Keys a.k.a. Last In Wins !!

● Primary Keys + Changed Columns

● Primary Keys + All Columns

● Primary Keys + Timestamp/rowversion

● Show me some code man !!


Optimistic ConcurrencyOptimistic Concurrency

● Let us examine each concurrency model one by one.

● First we need a database structure.

● Three tables, hierarchically arranged

● Animals

● Pets

● PetBelonging

● Just run Sql\database setup script.sql

● Let us examine each concurrency model one by one.

● First we need a database structure.

● Three tables, hierarchically arranged

● Animals

● Pets

● PetBelonging

● Just run Sql\database setup script.sql


Database DiagramDatabase Diagram


Code Example #1Code Example #1

● Create an application using Drag Drop that works with the Pets table.

● Run two instances, execute parallel inserts

● You will see that the primary key is automatically resolved.

● Next run two instances, and execute parallel updates.

● You should get a concurrency violation.

● Demonstrate the various commands being generated by the TableAdapter

● Create an application using Drag Drop that works with the Pets table.

● Run two instances, execute parallel inserts

● You will see that the primary key is automatically resolved.

● Next run two instances, and execute parallel updates.

● You should get a concurrency violation.

● Demonstrate the various commands being generated by the TableAdapter


PetsTableAdapter.InitAdapterPetsTableAdapter.InitAdapter

● Demonstrate the DeleteCommand, InsertCommand, UpdateCommand texts in PetsTableAdapter.InitAdapter

● These commands check for the primary key and all columns involved.

● The most database portable concurrency check.

● First in wins !!

● Not too efficient.

● Demonstrate the DeleteCommand, InsertCommand, UpdateCommand texts in PetsTableAdapter.InitAdapter

● These commands check for the primary key and all columns involved.

● The most database portable concurrency check.

● First in wins !!

● Not too efficient.


Optimistic Concurrency – Only PKOptimistic Concurrency – Only PK

● Check only for primary keys.

● Effectively, don’t check for concurrency.

● Check only for primary keys.

● Effectively, don’t check for concurrency.


AnimalID AnimalType

AnimalWeight

1 Puppy 3 lbs

AnimalID AnimalType

AnimalWeight

1 Dog 50 lbs

AnimalID AnimalType

AnimalWeight

1 Mutt 50 lbs

Database


AnimalID AnimalType

AnimalWeight

1 Dog 50 lbs

AnimalID AnimalType

AnimalWeight

1 Mutt 50 lbs

Database



-- Erick’s Select querySelect AnimalID, AnimalType, AnimalWeight from Animals

-- Frans’ Select querySelect AnimalID, AnimalType, AnimalWeight from Animals

-- Erick’s update queryUpdate Animals Set AnimalType = 'Dog', AnimalWeight = '50 lbs' where AnimalID = 1

-- Frans’ update queryUpdate Animals Set AnimalType = 'Mutt', AnimalWeight = '50 lbs' where AnimalID = 1

-- Erick’s Select querySelect AnimalID, AnimalType, AnimalWeight from Animals

-- Frans’ Select querySelect AnimalID, AnimalType, AnimalWeight from Animals

-- Erick’s update queryUpdate Animals Set AnimalType = 'Dog', AnimalWeight = '50 lbs' where AnimalID = 1

-- Frans’ update queryUpdate Animals Set AnimalType = 'Mutt', AnimalWeight = '50 lbs' where AnimalID = 1



● Database portable, but doesn’t do anything to prevent data corruption.

● Good performance (because it doesn’t do anything).

● Database portable, but doesn’t do anything to prevent data corruption.

● Good performance (because it doesn’t do anything).


OC – PK + Changed ColumnsOC – PK + Changed Columns

● This approach checks the PK and all changed columns.

● It is database portable.

● But it does not guarantee reliability in all situations.

● This approach checks the PK and all changed columns.

● It is database portable.

● But it does not guarantee reliability in all situations.


AnimalID AnimalType

AnimalWeight

1 Puppy 3 lbs

AnimalID AnimalType

AnimalWeight

1 Dog 50 lbs1 Puppy 3 lbs

AnimalID AnimalType

AnimalWeight

1 Puppy 60 lbs1 Puppy 3 lbs

Database


AnimalID AnimalType

AnimalWeight

1 Dog 50 lbs1 Puppy 3 lbs

AnimalID AnimalType

AnimalWeight

1 Puppy 60 lbs1 Puppy 3 lbs

Database


OC –PK + Changed ColumnsOC –PK + Changed Columns

-- Erick’s Select querySelect AnimalID, AnimalType, AnimalWeight from Animals-- Frans’ Select querySelect AnimalID, AnimalType, AnimalWeight from Animals-- Erick’s update queryUpdate Animals Set AnimalType = 'Dog', AnimalWeight = '50 lbs' where AnimalID = 1 and AnimalWeight = '3 lbs' and AnimalType

= 'Puppy'-- Frans’ update query, this will now fail.Update Animals Set AnimalWeight = '60 lbs' where AnimalID = 1 and AnimalWeight = '3 lbs'

-- Erick’s Select querySelect AnimalID, AnimalType, AnimalWeight from Animals-- Frans’ Select querySelect AnimalID, AnimalType, AnimalWeight from Animals-- Erick’s update queryUpdate Animals Set AnimalType = 'Dog', AnimalWeight = '50 lbs' where AnimalID = 1 and AnimalWeight = '3 lbs' and AnimalType

= 'Puppy'-- Frans’ update query, this will now fail.Update Animals Set AnimalWeight = '60 lbs' where AnimalID = 1 and AnimalWeight = '3 lbs'


OC – PK + Changed ColumnsOC – PK + Changed Columns

● Better performance than checking all columns.

● Database portable.

● But this approach has a sinister hole !!!

● Better performance than checking all columns.

● Database portable.

● But this approach has a sinister hole !!!


-- Erick’s Select query

Select AnimalID, AnimalType, AnimalWeight from Animals

-- Frans’ Select query


-- Erick’s update query

Update Animals

Set AnimalType = 'Dog', AnimalWeight = '50 lbs'

where

AnimalID = 1 and AnimalWeight = '3 lbs' and AnimalType = 'Puppy'

-- Frans’ update query, this will now fail.

Update Animals

Set AnimalWeight = '60 lbs'

where

AnimalID = 1 and AnimalWeight = '3 lbs'

-- Erick’s Select query


-- Frans’ Select query


-- Erick’s update query

Update Animals

Set AnimalType = 'Dog', AnimalWeight = '50 lbs'

where

AnimalID = 1 and AnimalWeight = '3 lbs' and AnimalType = 'Puppy'

-- Frans’ update query, this will now fail.

Update Animals

Set AnimalWeight = '60 lbs'

where


So what does Frans do next?


-- Frans’ Select query (Second pass)Select AnimalID, AnimalType, AnimalWeight from Animals-- Frans’ Select query (Second pass)Select AnimalID, AnimalType, AnimalWeight from Animals

-- Frans’ update query

Update Animals

AnimalWeight = '60 lbs'

where


-- Sushil’s Select query


-- Sushil’s Update query

Update Animals

Set AnimalType = 'Monkey'

where

AnimalID = 1 and AnimalType = 'Dog'

-- Pablo’s Select query (Second pass)Select AnimalID, AnimalType, AnimalWeight from Animals


Final ResultsFinal Results

Erick – Dog 50 lbs

Erick – Dog 50 lbs Sushil –

Monkey 50 lbs

Frans – Dog 60 lbs


Final Actual Database ResultsFinal Actual Database Results

Pablo – Monkey – 60 lbsPablo – Monkey – 60 lbs


Optimistic Concurrency - TimestampsOptimistic Concurrency - Timestamps

● Sql Server specific feature.

● Sql server supports a column type called timestamp.

● Timestamp is actually rowversion

● T-SQL Timestamp = SQL-92 standard’s datetime.

● One day in the future microsoft may decide to deprecate timestamp and ask you to use rowversion instead.

● Sql Server specific feature.

● Sql server supports a column type called timestamp.

● Timestamp is actually rowversion

● T-SQL Timestamp = SQL-92 standard’s datetime.

● One day in the future microsoft may decide to deprecate timestamp and ask you to use rowversion instead.


Code demonstrationCode demonstration

● Show how the following work

● UpdateCommand

● DeleteCommand (Beta2 bug)

● InsertCommand

● Show the significance of

● AcceptChangesDuringUpdate

● ContinueUpdateOnError

● Show how the following work

● UpdateCommand

● DeleteCommand (Beta2 bug)

● InsertCommand

● Show the significance of

● AcceptChangesDuringUpdate

● ContinueUpdateOnError


Code DemonstrationCode Demonstration

● Hierarchical Updates and Hierarchical update concerns.

● Insert Order

● Update Order

● Delete Order

● Concurrency in Hierarchical updates.

● Hierarchical Updates and Hierarchical update concerns.

● Insert Order

● Update Order

● Delete Order

● Concurrency in Hierarchical updates.


End NotesEnd Notes

● Thank you !!

● Questions?

● Contact me – ● http://www.winsmarts.com/contact.aspx

● Thank you !!

● Questions?

● Contact me – ● http://www.winsmarts.com/contact.aspx

Sofia, Bulgaria | 9-10 October Concurrency Management – ADO.NET 2.0 Presented By: Sahil Malik ...

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