Re: what can a sequence of handler::index_XXX be interrupted by?

One last question on this. Each of the handlers below in the index
merge/intersection code. Will each of the handlers be calling
index_XXX() on a different index? Or is it possible that two of them
may be called on the same index?

Thanks
-Zardosht

On Wed, Jul 27, 2011 at 1:28 PM, Sergey Petrunya <[email protected]> wrote:
> On Tue, Jul 26, 2011 at 06:13:54PM -0400, Zardosht Kasheff wrote:
>> For the last case, where we have:
>> >    handlers[0]->index_XXX();
>> >    handlers[1]->index_XXX();
>> >    handlers[2]->index_XXX();
>> >    handlers[0]->index_XXX();
>> >    handlers[0]->index_XXX();
>> >    handlers[1]->index_XXX();
>>
>> I assume each of the handlers share the same thd object? So if I check
>> the thd object for each of the handlers, I will get the same one?
>
> Yes. handlers[i]->ha_thd() == handlers[j]->ha_thd() for any i and j.
>
>> I guess here is another question. Is there any way for a handler with
>> some thd object be blocked from executing until some operation with
>> ANOTHER thd finishes. For instance, in the above example, handlers[1]
>> cannot execute until handlers[0] performs its index_XXX function, but
>> (I hope) they have the same thd.
>
> Every query is executed by some particular thread, and all ha_xxx objects
> used by a thread must have their thd equal to thread's thd. This means that
> the blockings you're interested in cannot be caused by a single query.
>
> As for multiple queries, I can only think of locking:
> - If your storage engine's ha_xxx::store_lock() produces lock objects that are
>  exclusive for one another, then the blocking may occur
> - I suspect something similar can happen with DDL operations. if there is a
>  DDL operation running, other threads won't be able to open the table until
>  the DDL op has finished.
>
> BR
>  Sergey
> --
> Sergey Petrunia, Software Developer
> Monty Program AB, http://askmonty.org
> Blog: http://s.petrunia.net/blog
>

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