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

On Mon, Sep 28, 2015 at 7:09 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:

>
> 2015-09-28 12:37 GMT+02:00 Shulgin, Oleksandr <
> oleksandr(dot)shulgin(at)zalando(dot)de>:
>
>>
>>> I didn't propose too different solution. There is only one difference -
>>> sharing DSM for smaller data. It is similar to using usual shared memory.
>>>
>>
>> Does this mean implementing some sort of allocator on top of the shared
>> memory segment? If so, how are you going to prevent fragmentation?
>>
>
> yes, simple memory allocator is necessary in this case. But it should be
> really simple - you can allocate only fixed size blocks - 10KB, 100KB and
> 1MB from separate buffers. So the fragmentation is not possible.
>

Maybe we're talking about completely different ideas, but I don't see how
fixing the block helps to fight fragmentation, in particular. Can you
sketch a simple example? E.g. 400 backends share the common segment and
all of them want to publish a plan of ~1kb, for example. Now what?

--
Alex