Hi,
On 2021-04-25 03:58:38 +1200, David Rowley wrote:
> Currently, we use dynahash hash tables to store the SMgrRelation so we
> can perform fast lookups by RelFileNodeBackend. However, I had in mind
> that a simplehash table might perform better. So I tried it...
> The test case was basically in
On Tue, Oct 05, 2021 at 11:07:48AM +1300, David Rowley wrote:
> I think I'd much rather talk about the concerns here than just
> withdraw this. Even if what I have today just serves as something to
> aid discussion.
Hmm. This last update was two months ago, and the patch does not
apply anymore.
Good day, David and all.
В Вт, 05/10/2021 в 11:07 +1300, David Rowley пишет:
> On Mon, 4 Oct 2021 at 20:37, Jaime Casanova
> wrote:
> > Based on your comments I will mark this patch as withdrawn at midday
> > of
> > my monday unless someone objects to that.
>
> I really think we need a hash tabl
On Mon, 4 Oct 2021 at 20:37, Jaime Casanova
wrote:
> Based on your comments I will mark this patch as withdrawn at midday of
> my monday unless someone objects to that.
I really think we need a hash table implementation that's faster than
dynahash and supports stable pointers to elements (simpleh
On Mon, Sep 27, 2021 at 04:30:25PM +1300, David Rowley wrote:
> On Fri, 24 Sept 2021 at 20:26, Jaime Casanova
> wrote:
> > Are you planning to work on this in this CF?
> > This is marked as "Ready for committer" but it doesn't apply anymore.
>
> I've attached an updated patch. Since this patch is
On Fri, 24 Sept 2021 at 20:26, Jaime Casanova
wrote:
> Are you planning to work on this in this CF?
> This is marked as "Ready for committer" but it doesn't apply anymore.
I've attached an updated patch. Since this patch is pretty different
from the one that was marked as ready for committer, I'l
On Tue, Jun 22, 2021 at 02:15:26AM +1200, David Rowley wrote:
[...]
>
> I've come up with a new hash table implementation that I've called
> generichash. It works similarly to simplehash in regards to the
Hi David,
Are you planning to work on this in this CF?
This is marked as "Ready for commi
On Thu, 1 Jul 2021 at 13:00, Thomas Munro wrote:
>
> On Wed, Jun 30, 2021 at 11:14 PM David Rowley wrote:
> > 1) Since I really need 8-byte buckets in the hash table to make this
> > as fast as possible, I want to use the array index for the hash status
> > and that means changing the simplehash
On Wed, Jun 30, 2021 at 11:14 PM David Rowley wrote:
> On Wed, 23 Jun 2021 at 12:17, Thomas Munro wrote:
> Thanks for taking an interest in this. I started looking at your idea
> and I've now changed my mind from just not liking it to thinking that
> the whole idea is just completely horrible :-(
On Wed, 23 Jun 2021 at 12:17, Thomas Munro wrote:
>
> David and I discussed this a bit off-list, and I just wanted to share
> how I understand the idea so far in case it helps someone else. There
> are essentially three subcomponents working together:
Thanks for taking an interest in this. I sta
On Tue, Jun 22, 2021 at 6:51 PM David Rowley wrote:
> I guess we could also ask ourselves how many join algorithms we need.
David and I discussed this a bit off-list, and I just wanted to share
how I understand the idea so far in case it helps someone else. There
are essentially three subcompone
On Tue, Jun 22, 2021 at 1:55 PM David Rowley wrote:
> On Tue, 22 Jun 2021 at 03:43, Tom Lane wrote:
> > I kind of wonder if we really need four different hash table
> > implementations (this being the third "generic" one, plus hash join
> > has its own, and I may have forgotten others). Should w
On Tue, 22 Jun 2021 at 03:43, Tom Lane wrote:
> I kind of wonder if we really need four different hash table
> implementations (this being the third "generic" one, plus hash join
> has its own, and I may have forgotten others). Should we instead
> think about revising simplehash to gain the benef
On Tue, 22 Jun 2021 at 02:53, Robert Haas wrote:
> At the risk of kibitzing the least-important detail of this proposal,
> I'm not very happy with the names of our hash implementations.
> simplehash is not especially simple, and dynahash is not particularly
> dynamic, especially now that the main
Robert Haas writes:
> On Mon, Jun 21, 2021 at 10:15 AM David Rowley wrote:
>> I've come up with a new hash table implementation that I've called
>> generichash.
> At the risk of kibitzing the least-important detail of this proposal,
> I'm not very happy with the names of our hash implementations
On Mon, Jun 21, 2021 at 10:15 AM David Rowley wrote:
> I've come up with a new hash table implementation that I've called
> generichash.
At the risk of kibitzing the least-important detail of this proposal,
I'm not very happy with the names of our hash implementations.
simplehash is not especiall
I'd been thinking of this patch again. When testing with simplehash,
I found that the width of the hash bucket type was fairly critical for
getting good performance from simplehash.h. With simplehash.h I
didn't manage to narrow this any more than 16 bytes. I needed to store
the 32-bit hash value
The following review has been posted through the commitfest application:
make installcheck-world: tested, passed
Implements feature: tested, passed
Spec compliant: tested, passed
Documentation:not tested
I believe it is ready for committer.
The new status of this patc
Hey David,
> I think you'd have to batch by filenode and transaction in that case. Each
> batch might be pretty small on a typical OLTP workload, so it might not help
> much there, or it might hinder.
True, it is very workload dependent (I was chasing mainly INSERTs multiValues,
INSERT-SELECT)
Hi Jakub,
On Wed, 5 May 2021 at 20:16, Jakub Wartak wrote:
> I might be a little bit out of the loop, but as Alvaro stated - Thomas did
> plenty of excellent job related to recovery performance in that thread. In my
> humble opinion and if I'm not mistaken (I'm speculating here) it might be
>
Hi David, Alvaro, -hackers
> Hi David,
>
> You're probably aware of this, but just to make it explicit: Jakub Wartak was
> testing performance of recovery, and one of the bottlenecks he found in
> some of his cases was dynahash as used by SMgr. It seems quite possible
> that this work would ben
Hi David,
You're probably aware of this, but just to make it explicit: Jakub
Wartak was testing performance of recovery, and one of the bottlenecks
he found in some of his cases was dynahash as used by SMgr. It seems
quite possible that this work would benefit some of his test workloads.
He last
I've attached an updated patch. I forgot to call SH_ENTRY_CLEANUP,
when it's defined during SH_RESET.
I also tided up a couple of comments and change the code to use
pg_rotate_right32(.., 31) instead of adding a new function for
pg_rotate_left32 and calling that to shift left 1 bit.
David
v3-0
On Thu, 29 Apr 2021 at 12:30, Yura Sokolov wrote:
>
> David Rowley писал 2021-04-29 02:51:
> > Another line of thought for making it go faster would be to do
> > something like get rid of the hash status field from SMgrEntry. That
> > could be either coded into a single bit we'd borrow from the h
David Rowley писал 2021-04-29 02:51:
On Thu, 29 Apr 2021 at 00:28, Yura Sokolov
wrote:
The best result is with just:
return (uint32)rnode->node.relNode;
ie, relNode could be taken without mixing at all.
relNode is unique inside single database, and almost unique among
whole
cluster
sinc
On Thu, 29 Apr 2021 at 00:28, Yura Sokolov wrote:
> The best result is with just:
>
> return (uint32)rnode->node.relNode;
>
> ie, relNode could be taken without mixing at all.
> relNode is unique inside single database, and almost unique among whole
> cluster
> since it is Oid.
I admit to hav
David Rowley писал 2021-04-26 09:43:
I tried that and it got a median result of 113.795 seconds over 14
runs with this recovery benchmark test.
LOG: size: 4096, members: 2032, filled: 0.496094, total chain: 1014,
max chain: 6, avg chain: 0.499016, total_collisions: 428,
max_collisions: 3, avg_c
Hi,
On 2021-04-26 22:44:13 +0300, Yura Sokolov wrote:
> Even for Robin Hood hashing 0.9 fill factor is too high. It leads to too
> much movements on insertion/deletion and longer average collision chain.
That's true for modification heavy cases - but most hash tables in PG,
including the smgr one
Andres Freund писал 2021-04-26 21:46:
Hi,
On 2021-04-25 01:27:24 +0300, Yura Sokolov wrote:
It is quite interesting result. Simplehash being open-addressing with
linear probing is friendly for cpu cache. I'd recommend to define
SH_FILLFACTOR with value lower than default (0.9). I believe 0.75 i
Hi,
On 2021-04-25 01:27:24 +0300, Yura Sokolov wrote:
> It is quite interesting result. Simplehash being open-addressing with
> linear probing is friendly for cpu cache. I'd recommend to define
> SH_FILLFACTOR with value lower than default (0.9). I believe 0.75 is
> suitable most for such kind of
On Mon, 26 Apr 2021 at 05:03, Yura Sokolov wrote:
> If your test so sensitive to hash function speed, then I'd suggest
> to try something even simpler:
>
> static inline uint32
> relfilenodebackend_hash(RelFileNodeBackend *rnode)
> {
> uint32 h = 0;
> #define step(x) h ^= (uint32)
David Rowley писал 2021-04-25 16:36:
On Sun, 25 Apr 2021 at 18:48, Yura Sokolov
wrote:
If you read comments in SH_START_ITERATE, you'll see:
* Search for the first empty element. As deletions during
iterations
are
* supported, we want to start/end at an element that cannot be
affected
On Sun, 25 Apr 2021 at 18:48, Yura Sokolov wrote:
> If you read comments in SH_START_ITERATE, you'll see:
>
>* Search for the first empty element. As deletions during iterations
> are
>* supported, we want to start/end at an element that cannot be
> affected
>* by elements being shifte
David Rowley писал 2021-04-25 05:23:
Thanks for having a look at this.
"On Sun, 25 Apr 2021 at 10:27, Yura Sokolov
wrote:
It is quite interesting result. Simplehash being open-addressing with
linear probing is friendly for cpu cache. I'd recommend to define
SH_FILLFACTOR with value lower th
Thanks for having a look at this.
"On Sun, 25 Apr 2021 at 10:27, Yura Sokolov wrote:
>
> It is quite interesting result. Simplehash being open-addressing with
> linear probing is friendly for cpu cache. I'd recommend to define
> SH_FILLFACTOR with value lower than default (0.9). I believe 0.75 i
David Rowley писал 2021-04-24 18:58:
Hackers,
Last year, when working on making compactify_tuples() go faster for
19c60ad69, I did quite a bit of benchmarking of the recovery process.
The next thing that was slow after compactify_tuples() was the hash
lookups done in smgropen().
Currently, we u
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