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Thread: Partial match fix for fast scan

Partial match fix for fast scan

From
Alexander Korotkov
Date:
Hi,

GIN partial match appears to be broken after fast scan. Following simple test case raises assertion failure.

create extension btree_gin;
create table test as (select id, random() as val from generate_series(1,1000000) id);
create index test_idx on test using gin (val);
vacuum test;
select * from test where val between 0.1 and 0.9;

Attached patch fixes bugs in entryGetItem function.
I would especially point that "continue;" checks "while" condition even if it's postfix "while". That's why I surrounded tbm_iterate with another "while".

------
With best regards,
Alexander Korotkov.
Attachment

Re: Partial match fix for fast scan

From
Fabrízio de Royes Mello
Date:

On Thu, Apr 10, 2014 at 11:09 AM, Alexander Korotkov <aekorotkov@gmail.com> wrote:
Hi,

GIN partial match appears to be broken after fast scan. Following simple test case raises assertion failure.

create extension btree_gin;
create table test as (select id, random() as val from generate_series(1,1000000) id);
create index test_idx on test using gin (val);
vacuum test;
select * from test where val between 0.1 and 0.9;

Attached patch fixes bugs in entryGetItem function.
I would especially point that "continue;" checks "while" condition even if it's postfix "while". That's why I surrounded tbm_iterate with another "while".


Interesting... to me (using current master) your test case doesn't fail...

fabrizio=# select * from test where val between 0.1 and 0.9;
   id   |        val       
--------+-------------------
      1 | 0.554413774050772
      2 | 0.767866868525743
      3 | 0.601187175605446
...


But fail if I change the values of between clause:

fabrizio=# select * from test where val between 0.1 and 0.19;
ERROR:  tuple offset out of range: 8080


Regards,

--
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL

Re: Partial match fix for fast scan

From
Alexander Korotkov
Date:
On Thu, Apr 10, 2014 at 8:22 PM, Fabrízio de Royes Mello <fabriziomello@gmail.com> wrote:

On Thu, Apr 10, 2014 at 11:09 AM, Alexander Korotkov <aekorotkov@gmail.com> wrote:
Hi,

GIN partial match appears to be broken after fast scan. Following simple test case raises assertion failure.

create extension btree_gin;
create table test as (select id, random() as val from generate_series(1,1000000) id);
create index test_idx on test using gin (val);
vacuum test;
select * from test where val between 0.1 and 0.9;

Attached patch fixes bugs in entryGetItem function.
I would especially point that "continue;" checks "while" condition even if it's postfix "while". That's why I surrounded tbm_iterate with another "while".


Interesting... to me (using current master) your test case doesn't fail...

fabrizio=# select * from test where val between 0.1 and 0.9;
   id   |        val       
--------+-------------------
      1 | 0.554413774050772
      2 | 0.767866868525743
      3 | 0.601187175605446
...


But fail if I change the values of between clause:

fabrizio=# select * from test where val between 0.1 and 0.19;
ERROR:  tuple offset out of range: 8080


It must be compiled with --enable-cassert to fail on assertion. 

------
With best regards,
Alexander Korotkov. 

Re: Partial match fix for fast scan

From
Heikki Linnakangas
Date:
On 04/10/2014 10:00 PM, Alexander Korotkov wrote:
> On Thu, Apr 10, 2014 at 8:22 PM, Fabrízio de Royes Mello <
> fabriziomello@gmail.com> wrote:
>
>> On Thu, Apr 10, 2014 at 11:09 AM, Alexander Korotkov <aekorotkov@gmail.com
>>> wrote:
>>
>>> GIN partial match appears to be broken after fast scan. Following simple
>>> test case raises assertion failure.
>>>
>>> create extension btree_gin;
>>> create table test as (select id, random() as val from
>>> generate_series(1,1000000) id);
>>> create index test_idx on test using gin (val);
>>> vacuum test;
>>> select * from test where val between 0.1 and 0.9;
>>>
>>> Attached patch fixes bugs in entryGetItem function.
>>> I would especially point that "continue;" checks "while" condition even
>>> if it's postfix "while". That's why I surrounded tbm_iterate with another
>>> "while".
>>>
>>>
>> Interesting... to me (using current master) your test case doesn't fail...
>>
>> fabrizio=# select * from test where val between 0.1 and 0.9;
>>     id   |        val
>> --------+-------------------
>>        1 | 0.554413774050772
>>        2 | 0.767866868525743
>>        3 | 0.601187175605446
>> ...
>>
>>
>> But fail if I change the values of between clause:
>>
>> fabrizio=# select * from test where val between 0.1 and 0.19;
>> ERROR:  tuple offset out of range: 8080
>>
>
>
> It must be compiled with --enable-cassert to fail on assertion.

I'm actually getting the "tuple offset out of range" with Fabrizio's 
query, even after your fix (not every time, run it a few times, 
launching a new connection each time). So there's another bug lurking 
there. The problem seems to be that even though we've checked in the 
innermost loop that not all of the items on the page are <= advancePast, 
that situation can change later if advancePast is advanced. So on next 
invocation entryGetItem, the loop to skip past advancePast might read 
bogus offsets in the array.

I pushed a patch, which includes Alexander's fix, and also fixes the 
second issue.

- Heikki