Re: Assert failure on 'list_member_ptr(rel->joininfo, restrictinfo)'
| От | Alexander Korotkov |
|---|---|
| Тема | Re: Assert failure on 'list_member_ptr(rel->joininfo, restrictinfo)' |
| Дата | |
| Msg-id | CAPpHfduwr9c6opkAPg_6hv+Adma0U41C=ZsuYCUVENa+3sgcnA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Assert failure on 'list_member_ptr(rel->joininfo, restrictinfo)' (Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>) |
| Ответы |
Re: Assert failure on 'list_member_ptr(rel->joininfo, restrictinfo)'
(Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>)
Re: Assert failure on 'list_member_ptr(rel->joininfo, restrictinfo)' (Alexander Korotkov <aekorotkov@gmail.com>) |
| Список | pgsql-hackers |
On Fri, Dec 8, 2023 at 11:24 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> On Fri, Dec 8, 2023 at 3:28 PM Ashutosh Bapat
> <ashutosh.bapat.oss@gmail.com> wrote:
> > I did some analysis of memory consumption by bitmapsets in such cases.
> > [1] contains slides with the result of this analysis. The slides are
> > crude and quite WIP. But they will give some idea.
> >
> > [1] https://docs.google.com/presentation/d/1S9BiAADhX-Fv9tDbx5R5Izq4blAofhZMhHcO1c-wzfI/edit?usp=sharing
>
> Thank you for sharing your analysis. I understand that usage of a
> plain bitmap becomes a problem with a large number of partitions. But
> I wonder what does "post proposed fixes" mean? Is it the fixes posted
> in [1]. If so it's very surprising for me they are reducing the
> memory footprint size.
No. These are fixes in various threads all listed together in [1]. I
had started investigating memory consumption by Bitmapsets around the
same time. The slides are result of that investigation. I have updated
slides with this reference.
[1] https://www.postgresql.org/message-id/CAExHW5s_KwB0Rb9L3TuRJxsvO5UCtEpdskkAeMb5X1EtssMjgg@mail.gmail.com
They reduce the memory footprint by Bitmapset because they reduce the
objects that contain the bitmapsets, thus reducing the total number of
bitmapsets produced.
Thank you Ashutosh for your work on this matter. With a large number of partitions, it definitely makes sense to reduce both Bitmapset's size as well as the number of Bitmapsets.
I've checked the patchset [1] with your test suite to check the memory consumption. The results are in the table below.
----------------------------------------------------------------------------------
2-way join, non partitioned | 14792 | 15208 | 29152
2-way join, no partitionwise join | 19519576 | 19519576 | 19519576
2-way join, partitionwise join | 40851968 | 40851968 | 40851968
3-way join, non partitioned | 20632 | 21784 | 79376
3-way join, no partitionwise join | 45227224 | 45227224 | 45227224
3-way join, partitionwise join | 151655144 | 151655144 | 151655144
4-way join, non partitioned | 25816 | 27736 | 209128
4-way join, no partitionwise join | 83540712 | 83540712 | 83540712
4-way join, partitionwise join | 463960088 | 463960088 | 463960088
5-way join, non partitioned | 31000 | 33720 | 562552
5-way join, no partitionwise join | 149284376 | 149284376 | 149284376
5-way join, partitionwise join | 1663896608 | 1663896608 | 1663896608
The most noticeable thing for me is that self-join removal doesn't work with partitioned tables. I think this is the direction for future work on this subject. In non-partitioned cases, patchset gives a small memory overhead. However, the memory consumption is still much less than it is without the self-join removal. So, removing the join still lowers memory consumption even if it copies some Bitmapsets. Given that patchset [1] is required for the correctness of memory manipulations in Bitmapsets during join removals, I'm going to push it if there are no objections.
Links.
1. https://www.postgresql.org/message-id/CAPpHfdtLgCryACcrmLv%3DKoq9rAB3%3Dtr5y9D84dGgvUhSCvjzjg%40mail.gmail.com
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Regards,
Regards,
Alexander Korotkov
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