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Re: [CFReview] Red-Black Treey

From: Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>
To: Mark Cave-Ayland <mark(dot)cave-ayland(at)siriusit(dot)co(dot)uk>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Teodor Sigaev <teodor(at)sigaev(dot)ru>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [CFReview] Red-Black Treey
Date: 2010-01-29 18:52:07
Message-ID: Pine.LNX.4.64.1001292150010.16860@sn.sai.msu.ru (view raw or flat)
Thread:
Lists: pgsql-hackers
Mark, do you need my data to reproduce results from
http://www.sai.msu.su/~megera/wiki/2009-07-27 ?

Oleg
On Fri, 29 Jan 2010, Mark Cave-Ayland wrote:

> Hi Robert,
>
> I've also spent some time reviewing this patch since it is a
> pre-requisite to the KNNGiST patch. I did have a much more comprehensive
> list of suggestions, but it seems you've managed to resolve most of
> these with your latest re-write. Please find some more comments inline:
>
>> Here's an edited version, which I've now reviewed more fully.  Some
>> more substantive review comments:
>
> Firstly: the re-worked patch that you have posted seems to contain
> remnants of at least 2 other patches. I have extracted the rbtree-only 
> sections and re-attached to this email.
>
> The patch was tested against git head 124a3cc... and applied without any 
> fuzz or other issues.
>
>> 1. I'm pretty satisfied that the rbtree code is generally sane,
>> although I wonder if we should think about putting it in access/common
>> rather than utils/misc.  I'm not sure that I have a sufficiently
>> clearly defined notion of what each subdirectory is for to draw a
>> definitive conclusion on this point; hopefully someone else will weigh
>> in.
>
> I'm happy that the code is a reasonable implementation of an RB-Tree, at
> least with respect to the link to the related public domain source that
> was posted. In terms of location, I think utils/misc is a reasonable
> place for it to live since I see it as analogous to the hash table
> implementation, i.e. it's a template RB-Tree implementation designed to
> be used as required throughout the codebase. backend/access seems to be
> the home of index AMs only.
>
> Other code points:
>
> - The new names for the iterator enum seem much better to me - or at
> least it helped understand the meaning of the iterator code.
>
> - You correctly picked up on the namespace issue, although I noticed
> that you left RED and BLACK as they were. Maybe RBRED and RBBLACK would
> be better, though not that there are any colour related defines around
> in a database backend to make a name clash probable.
>
> - I found the name of the "appendator" method misleading - perhaps
> "updater" would make more sense?
>
>> 2. I'm a little concerned about the performance implications of this
>> patch.  Looking at http://www.sai.msu.su/~megera/wiki/2009-04-03, it's
>> clear that the patch is a huge win in some cases.  But I'm also
>> surprised by how much performance is lost in some of the other cases
>> that you tested.  I suspect, on balance, that it's probably still a
>> good idea to put this in, but I wonder if you've profiled this at all
>> to see where the extra time is going and/or explored possible ways of
>> squashing that overhead down a little more.
>> 
>> 3. In ginInsertEntry(), the "else" branch of the if statement really
>> looks like magic when you first read it.  I wonder if it would make
>> sense to pull the contents of EAAllocate() directly into this
>> function, since there's only one call site anyhow.
>
> God yes. This is not a good example of maintainable code - even with your 
> comment I struggled for a while to try and figure it out :(  I would suggest 
> that this is refactored appropriately before commit.
>
>> I still have not done any performance testing of my own on this code,
>> and it probably needs that.  If anyone else has time to step up and
>> help with that, it would be much appreciated.  It would be useful to
>> have some plain old benchmarks as well as some profiling data as
>> mentioned above.
>
> As part of my testing, I attempted to duplicate some of the benchmarks
> at http://www.sai.msu.su/~megera/wiki/2009-04-03. Unfortunately I was not 
> really able to reproduce the RND (teodor's) dataset, nor the random array 
> test as the SQL used to test the implementation was not present on the page 
> above.
>
> For each test, I dropped and recreated the database to ensure that any 
> autovacuum impact would be the same.
>
>
> 1) Fixed length random & sequential string arrays
>
> SELECT array_to_string(ARRAY(select '' || a || '.' || b from
> generate_series(1,50) b), ' ')::tsvector AS i INTO seq FROM
> generate_series(1,100000) a;
>
> SELECT array_to_string(ARRAY(select '' || random() from
> generate_series(1,50) b), ' ')::tsvector AS i INTO rnd FROM
> generate_series(1,100000) a;
>
>
> Before patch:
>
> test=# create index seq_idx on seq using gin (i);
> CREATE INDEX
> Time: 103205.790 ms
> test=# create index rnd_idx on rnd using gin (i);
> CREATE INDEX
> Time: 6770.131 ms
>
>
> After patch:
>
> test=# create index seq_idx on seq using gin (i);
> CREATE INDEX
> Time: 87724.953 ms
> test=# create index rnd_idx on rnd using gin (i);
> CREATE INDEX
> Time: 5596.666 ms
>
>
> 2) Identical records, variable length test
>
> select ARRAY(select generate_series(1,len)) as a50  into arr50 from 
> generate_series(1,100000) b;
>
>
> Before patch:
>
> i) len=3
>
> select ARRAY(select generate_series(1,3)) as a3 into arr3 from 
> generate_series(1,100000) b;
>
> test=# create index arr3_idx on arr3 using gin (a3);
> CREATE INDEX
> Time: 324.251 ms
>
>
> ii) len=30
>
> select ARRAY(select generate_series(1,30)) as a30 into arr30 from 
> generate_series(1,100000) b;
>
> test=# create index arr30_idx on arr30 using gin (a30);
> CREATE INDEX
> Time: 2163.786 ms
>
>
> iii) len=50
>
> select ARRAY(select generate_series(1,50)) as a50 into arr50 from 
> generate_series(1,100000) b;
>
> test=# create index arr50_idx on arr50 using gin (a50);
> CREATE INDEX
> Time: 3306.074 ms
>
>
> iv) len=random
>
> select ARRAY(select generate_series(1, (random() * 100)::int)) as arand into 
> arrrand from generate_series(1,100000) b;
>
> test=# create index arrrand_idx on arrrand using gin (arand);
> CREATE INDEX
> Time: 4725.556 ms
>
>
> After patch:
>
> i) len=3
>
> select ARRAY(select generate_series(1,3)) as a3 into arr3 from 
> generate_series(1,100000) b;
>
> test=# create index arr3_idx on arr3 using gin (a3);
> CREATE INDEX
> Time: 299.090 ms
>
>
> ii) len=30
>
> select ARRAY(select generate_series(1,30)) as a30 into arr30 from 
> generate_series(1,100000) b;
>
> test=# create index arr30_idx on arr30 using gin (a30);
> CREATE INDEX
> Time: 2828.424 ms
>
>
> iii) len=50
>
> select ARRAY(select generate_series(1,50)) as a50 into arr50 from 
> generate_series(1,100000) b;
>
> test=# create index arr50_idx on arr50 using gin (a50);
> CREATE INDEX
> Time: 3984.456 ms
>
>
> iv) len=random
>
> select ARRAY(select generate_series(1, (random() * 100)::int)) as arand into 
> arrrand from generate_series(1,100000) b;
>
> test=# create index arrrand_idx on arrrand using gin (arand);
> CREATE INDEX
> Time: 3514.972 ms
>
>
> Summary
> =======
>
> I believe Robert has done a good deal of the groundwork required to get this 
> patch ready for inclusion. With the current version, I was able to see a 
> measurable performance improvement in some test cases with no significant 
> performance regression. It would have been nice to be able to reproduce the 
> whole set of test cases but this was not possible from the information 
> specified.
>
> With perhaps some minor tweaks to some of the names and a rework of the else 
> clause in ginInsertEntry(), I feel this patch is reasonably close to commit.
>
> I shall now continue my review of the associated KNNGiST patch.
>
>
> ATB,
>
> Mark.
>
>

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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