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How to solve the issue of multiple users doing the same logic on a record at the same time?

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Posted on by junior AX

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If i create a button that inserts records in a certain table when clicked. And i put the insert code inside a ttsbegin and ttscommit. Let's say 6 users clicked the same button at the same time. Does the ttsbegin and ttscommit make the other users wait until each user finishes or a deadlock will happen and what to do in order to avoid such error?

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zhifeng Microsoft Employee on at

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Would you please share more details about the customization? Are these 6 users touch same records or different records?

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junior AX 1,552 on at

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Let's say a button when you click it, it creates a new record by code in custTable with certain info. So they touch the same button

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Sergei Minozhenko 23,095 on at

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Hi Junior Ax,

Updates and deletes are controlled by the kernel and if multiple users edit or delete the same records, one of them gets an error message if another already performed action. Also, there is a locking mechanism on the SQL side that locks record if the update process already started. For new records, there is no such control, except unique indexes or custom code. In the case of customer creation, if 6 users press creates button 6 times - 6 customers will be created in case if you use number sequence for the customer form. If the account number is entered manually and users will enter the same account number, only one will be created and others will trigger errors.

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nmaenpaa 101,172 Moderator on at

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If your button creates a new record, then every user is actually working on their own separate (new) records. So there's no conflict, and everyone's transaction will succeed (assuming there's no duplicate Customer Id in the records).

If many users are really working on the same record, the system prevents conflicting changes to it. When record is selected for update, the system checks RecVersion of the record. When the actual update() is triggered, the system checks again, and if RecVersion was changed in the database meanwhile, an update conflict is raised and you can't update the record from your session. Instead you first need to refresh it. User will see error message like "One or more users updated the record, the values on the screen might not be up to date. Please refresh and try again".

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Leo Chen Microsoft Employee on at

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Agree with Nikolaos but just add some screenshots - There will be no conflict for multiple Inserts in same time. However for update/delete against same record, you'll see success messasge for the exact first transaction, while all rest transaction will fail with below error message showing in UI.

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junior AX 1,552 on at

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but the custTable has accountNum as a unique index so when 6 users click it at the same time, that means all the 6 users will try to take the same account Number. So isn't the logical output to be that one user will insert successfully and the others will get that the record already exists?

and the answer to my question when we get such errors, how can we handle them in code so that they won't appear to the user. I mean the code should make the others wait then proceed, isn't that doable?

One more thing, i tried to reproduce the issue but i got no errors: Am i not locking the same record in the code below?

try

{

ttsbegin;

while select forupdate custtable1 where custtable1.accountnum = "1"

{

select forupdate custtable2 where custtable2.accountNum ="1"

custtable2.update();

custtable1.update();

}

ttscommit;

}

catch

{

}

plus what is the difference between update conflicts and deadlock?

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nmaenpaa 101,172 Moderator on at

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Well, we don't know how you create the account numbers for the customers. If you take it from the number sequence, each 6 users would get a different number.

Remember that the more information you share with us, the better help you will get since we don't know anything about your solution except what you choose to tell us.

Update conflict means that two users tried to change the same record. This is triggered when the second update notices that RecVersion was changed. It's detected by Dynamics.

Deadlock happens on database level, when two update operations are waiting for locks from each other to get released.

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nmaenpaa 101,172 Moderator on at

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And in your code above, you didn't make any changes to the record so there's no conflict.

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Sukrut Parab 71,739 Moderator on at

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You should read about OCC and blog below to understand update conflict and deadlocks.

docs.microsoft.com/.../optimistic-concurrency-control

www.dynamicsaxtraining.com/.../what-is-lock-deadlock-in-dynamics-ax

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junior AX 1,552 on at

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I forgot to update the field. Below is the code. but still i get no errors. I think based on your definition this should be an update conflict because i'm trying to update the same record. but this should also be a deadlock because i'm locking the record and i'm trying to lock it again with the second select for update so the second select for update should wait for the first one? am i right? In my case i get no errors.

try { ttsbegin; while select forupdate custtable1 where custtable1.accountnum = "1" { custtable1.CustGroup = "1"; select forupdate custtable2 where custtable2.accountNum ="1" custtable2.CustGroup = 3; custtable2.update(); custtable1.update(); } ttscommit; } catch { }

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