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

Sofia, Bulgaria | 9-10 October About 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 (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 (that’s smart”S” with an “S”)

Sofia, Bulgaria | 9-10 October What is a concurrency conflict?

Sofia, Bulgaria | 9-10 October What is a concurrency conflict?

Sofia, Bulgaria | 9-10 October What is a concurrency conflict?

Sofia, Bulgaria | 9-10 October Database Example PersonIDExpenditure 1$ PersonIDExpenditure 1$ PersonIDExpenditure 1$ Spend $ 20 - Twice

Sofia, Bulgaria | 9-10 October Solution ●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.

Sofia, Bulgaria | 9-10 October Concurrency 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.

Sofia, Bulgaria | 9-10 October Conflict happens !! ●Pessimistic Locking ●Optimistic Concurrency Control ●Pessimistic Locking ●Optimistic Concurrency Control

Sofia, Bulgaria | 9-10 October Pessimistic Locking

Sofia, Bulgaria | 9-10 October Pessimistic Locking - Database Select Finger From GirlFriends HOLDLOCK Where GirlfriendName = ‘Jane’ Select Finger From GirlFriends HOLDLOCK Where GirlfriendName = ‘Jane’

Sofia, Bulgaria | 9-10 October Pessimistic 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.

Sofia, Bulgaria | 9-10 October Pessimistic 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?

Sofia, Bulgaria | 9-10 October Pessimistic 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.

Sofia, Bulgaria | 9-10 October Pessimistic 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.

Sofia, Bulgaria | 9-10 October Optimistic 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 !!

Sofia, Bulgaria | 9-10 October Optimistic 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

Sofia, Bulgaria | 9-10 October Database Diagram

Sofia, Bulgaria | 9-10 October Code 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

Sofia, Bulgaria | 9-10 October PetsTableAdapter.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.

Sofia, Bulgaria | 9-10 October Optimistic 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.

Sofia, Bulgaria | 9-10 October AnimalIDAnimalTypeAnimalWeight 1Puppy3 lbs AnimalIDAnimalTypeAnimalWeight 1Dog50 lbs AnimalIDAnimalTypeAnimalWeight 1Mutt50 lbs Database

Sofia, Bulgaria | 9-10 October AnimalIDAnimalTypeAnimalWeight 1Dog50 lbs AnimalIDAnimalTypeAnimalWeight 1Mutt50 lbs Database

Sofia, Bulgaria | 9-10 October Optimistic Concurrency – Only PK -- Erick’s Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- Frans’ Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- Erick’s update query Update Animals Set AnimalType = 'Dog', AnimalWeight = '50 lbs' where AnimalID = 1 -- Frans’ update query Update Animals Set AnimalType = 'Mutt', AnimalWeight = '50 lbs' where AnimalID = 1 -- Erick’s Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- Frans’ Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- Erick’s update query Update Animals Set AnimalType = 'Dog', AnimalWeight = '50 lbs' where AnimalID = 1 -- Frans’ update query Update Animals Set AnimalType = 'Mutt', AnimalWeight = '50 lbs' where AnimalID = 1

Sofia, Bulgaria | 9-10 October Optimistic Concurrency – Only PK ●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).

Sofia, Bulgaria | 9-10 October OC – 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.

Sofia, Bulgaria | 9-10 October AnimalIDAnimalTypeAnimalWeight 1Puppy3 lbs AnimalIDAnimalTypeAnimalWeight 1Dog50 lbs 1Puppy3 lbs AnimalIDAnimalTypeAnimalWeight 1Puppy60 lbs 1Puppy3 lbs Database

Sofia, Bulgaria | 9-10 October AnimalIDAnimalTypeAnimalWeight 1Dog50 lbs 1Puppy3 lbs AnimalIDAnimalTypeAnimalWeight 1Puppy60 lbs 1Puppy3 lbs Database

Sofia, Bulgaria | 9-10 October OC –PK + Changed Columns -- Erick’s Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- Frans’ Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- 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 Select AnimalID, AnimalType, AnimalWeight from Animals -- Frans’ Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- 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'

Sofia, Bulgaria | 9-10 October OC – 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 !!!

Sofia, Bulgaria | 9-10 October -- Erick’s Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- Frans’ Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- 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 Select AnimalID, AnimalType, AnimalWeight from Animals -- Frans’ Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- 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' So what does Frans do next?

Sofia, Bulgaria | 9-10 October -- 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 AnimalID = 1 and AnimalWeight = '50 lbs' -- Sushil’s Select query Select AnimalID, AnimalType, AnimalWeight from Animals -- 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

Sofia, Bulgaria | 9-10 October Final Results Erick – Dog 50 lbs Sushil – Monkey 50 lbs Frans – Dog 60 lbs

Sofia, Bulgaria | 9-10 October Final Actual Database Results Pablo – Monkey – 60 lbs

Sofia, Bulgaria | 9-10 October Optimistic 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.

Sofia, Bulgaria | 9-10 October Code 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

Sofia, Bulgaria | 9-10 October Code 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.

Sofia, Bulgaria | 9-10 October End Notes ●Thank you !! ●Questions? ●Contact me – ● ●Thank you !! ●Questions? ●Contact me – ●