2015-09-28 12:37 GMT+02:00 Shulgin, Oleksandr <oleksandr.shul...@zalando.de> :
> On Mon, Sep 28, 2015 at 12:05 PM, Pavel Stehule <pavel.steh...@gmail.com> > wrote: > >> >> 2015-09-28 12:01 GMT+02:00 Shulgin, Oleksandr < >> oleksandr.shul...@zalando.de>: >> >>> On Sun, Sep 27, 2015 at 8:05 AM, Pavel Stehule <pavel.steh...@gmail.com> >>> wrote: >>> >>> the preparing of content before execution is interesting idea, that can >>>> be used more. The almost queries and plans are not too big, so when the >>>> size of content is not too big - less than 1MB, then can be used one DSM >>>> for all backends. >>>> >>> >>> >>>> When size of content is bigger than limit, then DSM will be allocated >>>> specially for this content. The pointer to DSM and offset can be stored in >>>> requested process slot. The reading and writing to requested slot should be >>>> protected by spinlock, but it should block only two related processes for >>>> short time (copy memory). >>>> >>> >>> Sorry, I don't think this will fly. >>> >>> The whole idea is that a backend publishes the plan of a query just >>> before running it and it doesn't care which other backend(s) might be >>> reading it, how many times and in which order. The only required locking >>> (implicit) is contained in the code for dsm_attach/detach(). >>> >> >> 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. Regards Pavel > > -- > Alex > >
