Re: [Tcl-tdbc] tdbc::mysql and multiple threads...

[Georgios P. <pet...@ya...>]

On 2/9/2016 12:51, to...@tu... wrote:
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> On Fri, Sep 02, 2016 at 12:20:27PM +0300, Georgios Petasis wrote:
>> Hi all,
>>
>> I want to use a mysql database from multiple threads. What I do right
>> now, is to load the packages from multiple threads, and use the database
>> as I would from a single thread.
>>
>> The problem is that I am getting errors when beginning transactions. The
>> errors are about locks, timetouts, etc.
> [...]
>
> Sorry, not really specific to tdbc, but from what I know about other
> similar interfaces: the database connection has a state, and this
> state doesn't expect to be "seen" by independent entities (be it threads
> or whatever).
>
> Possible approaches:
>
>   (1) Set up a separate connection handle for each thread.
I am creating a separate connection for each thread. Each thread has its 
own connection.
I am at the tcl level, using the thread package.
>
>   (2) Use some cunning scheme which somehow manages this
>       state, creating an illusion of a private handle
>       per client (instance). Traditionally this is called
>       "connection pooling" and implemented by having one
>       thread handling the mess on behalf of the others.
>
> That said, perhaps ODBC is smarter than I think and pretends to do
> that for you: then that'd be a bug :-)
>
> (Sorry if you knew all of this. Perhaps I just failed to gather that
> from your question).
Since I have a new connection per thread, I was expecting that begin 
transaction/commit will be particular to each thread. However, they seem 
to interfere, and mysql client gets confused. Or I am using tdbc::mysql 
the wrong way.

Is there any tdbc example, that accesses (any) database with threads, 
and has transactions?

Thank you for your answer,

George