Re: On-demand running query plans using auto_explain and signals

2015-09-02 15:00 GMT+02:00 Shulgin, Oleksandr <oleksandr(dot)shulgin(at)zalando(dot)de>
:

> On Wed, Sep 2, 2015 at 2:56 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
>
>>
>>
>> 2015-09-02 12:36 GMT+02:00 Shulgin, Oleksandr <
>> oleksandr(dot)shulgin(at)zalando(dot)de>:
>>
>>> On Wed, Sep 2, 2015 at 11:16 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
>>> wrote:
>>>
>>>>
>>>>
>>>> 2015-09-02 11:01 GMT+02:00 Shulgin, Oleksandr <
>>>> oleksandr(dot)shulgin(at)zalando(dot)de>:
>>>>
>>>>> On Tue, Sep 1, 2015 at 7:02 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com
>>>>> > wrote:
>>>>>
>>>>>>
>>>>>>> But do we really need the slots mechanism? Would it not be OK to
>>>>>>> just let the LWLock do the sequencing of concurrent requests? Given that
>>>>>>> we only going to use one message queue per cluster, there's not much
>>>>>>> concurrency you can gain by introducing slots I believe.
>>>>>>>
>>>>>>
>>>>>> I afraid of problems on production. When you have a queue related to
>>>>>> any process, then all problems should be off after end of processes. One
>>>>>> message queue per cluster needs restart cluster when some pathological
>>>>>> problems are - and you cannot restart cluster in production week, sometimes
>>>>>> weeks. The slots are more robust.
>>>>>>
>>>>>
>>>>> Yes, but in your implementation the slots themselves don't have a
>>>>> queue/buffer. Did you intend to have a message queue per slot?
>>>>>
>>>>
>>>> The message queue cannot be reused, so I expect one slot per caller to
>>>> be used passing parameters, - message queue will be created/released by
>>>> demand by caller.
>>>>
>>>
>>> I don't believe a message queue cannot really be reused. What would
>>> stop us from calling shm_mq_create() on the queue struct again?
>>>
>>
>> you cannot to change recipient later
>>
>
> Well, maybe I'm missing something, but sh_mq_create() will just overwrite
> the contents of the struct, so it doesn't care about sender/receiver: only
> sh_mq_set_sender/receiver() do.
>

if you create sh_mq from scratch, then you can reuse structure.

Pavel