Re: Parallel Seq Scan
| От | Amit Kapila |
|---|---|
| Тема | Re: Parallel Seq Scan |
| Дата | |
| Msg-id | CAA4eK1+8h6KEdjZwJO8i7EbVC5w+wFQYZtg66Xj0o1zpTg_Zkw@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Parallel Seq Scan (Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>) |
| Ответы |
Re: Parallel Seq Scan
|
| Список | pgsql-hackers |
On Wed, Jan 21, 2015 at 12:47 PM, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp> wrote:
>
> On 20-01-2015 PM 11:29, Amit Kapila wrote:
> > Note - I have yet to handle the new node types introduced at some
> > of the places and need to verify prepared queries and some other
> > things, however I think it will be good if I can get some feedback
> > at current stage.
> >
>
> I got an assertion failure:
>
> In src/backend/executor/execTuples.c: ExecStoreTuple()
>
> /* passing shouldFree=true for a tuple on a disk page is not sane */
> Assert(BufferIsValid(buffer) ? (!shouldFree) : true);
>
> After fixing this, the assertion failure seems to be gone though I
> observed the blocked (CPU maxed out) state as reported elsewhere by Thom
> Brown.
>
>
> On 20-01-2015 PM 11:29, Amit Kapila wrote:
> > Note - I have yet to handle the new node types introduced at some
> > of the places and need to verify prepared queries and some other
> > things, however I think it will be good if I can get some feedback
> > at current stage.
> >
>
> I got an assertion failure:
>
> In src/backend/executor/execTuples.c: ExecStoreTuple()
>
> /* passing shouldFree=true for a tuple on a disk page is not sane */
> Assert(BufferIsValid(buffer) ? (!shouldFree) : true);
>
Good Catch!
The reason is that while master backend is scanning from a heap
page, if it finds another tuple/tuples's from shared memory message
queue it will process those tuples first and in such a scenario, the scan
descriptor will still have reference to buffer which it is using from scanning
from heap. Your proposed fix will work.
> After fixing this, the assertion failure seems to be gone though I
> observed the blocked (CPU maxed out) state as reported elsewhere by Thom
> Brown.
>
Does it happen only when parallel_seqscan_degree > max_worker_processes?
Thanks for checking the patch.
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