Re: Deadlocks and transactions

My application is a website.

Let´s suppose the following scenario.
* User 1 has already loaded a web page and clicks a button that triggers a
transaction that includes 2 tables.
* User 2 loads the same page and SELECTs data from the 2 tables currently
in the transaction generated by User 1. User 2 does not trigger a
transaction because he/she only gets data from the DB.

Is there any issue/problem for User 2?

(Is it correct to reply-to-all when posting back to a question?)

Best regards,
Jorge Maldonado

On Tue, Mar 20, 2018 at 4:01 AM, Lætitia Avrot <laetitia(dot)avrot(at)gmail(dot)com>
wrote:

> Hi Jorge,
>
> Here are the two advices I give developpers to reduce the risk a deadlock
> occures :
> - Always change(update, delete...) data in the same order
> - Keep your transactions short
>
> Cheers,
>
> Lætitia
>
> 2018-03-19 23:18 GMT+01:00 David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>:
>
>> On Mon, Mar 19, 2018 at 2:46 PM, JORGE MALDONADO <jorgemal1960(at)gmail(dot)com>
>> wrote:
>>
>>> I have a process that inserts a record in one table and, after that, a
>>> record in another table is updated. Because there are 2 DB operations, I
>>> decided to perform both of them in a transaction.
>>>
>>> Can a deadlock take place even if transactions are used?
>>>
>>
>> Its impossible to deadlock without transactions​.
>>
>> Simplistically, a deadlock happens when there are two processes - one
>> holds lock A and wants lock B while the other wants lock A while holding
>> lock B.
>>
>> Your choice to use a transaction here is good but you will have at least
>> some risk of deadlock with others parts of the system. Other processes
>> running this same exact code, however, should not pose a risk since the
>> locking order would be consistent.
>>
>> David J.
>>
>>
>