Re: POC, WIP: OR-clause support for indexes

On 25.11.2023 19:13, Alexander Korotkov wrote:
> On Sat, Nov 25, 2023 at 1:10 PM Alena Rybakina
> <a.rybakina@postgrespro.ru> wrote:
>> On 25.11.2023 04:13, Alexander Korotkov wrote:
>>
>> It seems to me there is a confusion.  I didn't mean we need to move
>> conversion of OR-expressions to ANY into choose_bitmap_and() function
>> or anything like this.  My idea was to avoid degradation of plans,
>> which I've seen in [1].  Current code for generation of bitmap paths
>> considers the possibility to split OR-expressions into distinct bitmap
>> index scans.  But it doesn't consider this possibility for
>> ANY-expressions.  So, my idea was to enhance our bitmap scan
>> generation to consider split values of ANY-expressions into distinct
>> bitmap index scans.  So, in the example [1] and similar queries
>> conversion of OR-expressions to ANY wouldn't affect the generation of
>> bitmap paths.
>>
>> Thanks for the explanation, yes, I did not understand the idea correctly at first. I will try to implement something
similar.
> Alena, great, thank you.  I'm looking forward to the updated patch.
>
I wrote the patch (any_to_or.diff.txt), although it is still under 
development (not all regression tests have been successful so far), it 
is already clear that for a query where a bad plan was chosen before, it 
is now choosing a more optimal query plan.

postgres=# set enable_or_transformation =on;
SET
postgres=# explain select * from test where (x = 1 or x = 2) and y = 100;
                                                   QUERY PLAN
--------------------------------------------------------------------------------------------------------------
  Bitmap Heap Scan on test  (cost=8.60..12.62 rows=1 width=12)
    Recheck Cond: (((y = '100'::double precision) AND (x = 1)) OR ((y = 
'100'::double precision) AND (x = 2)))
    ->  BitmapOr  (cost=8.60..8.60 rows=1 width=0)
          ->  Bitmap Index Scan on test_x_1_y  (cost=0.00..4.30 rows=1 
width=0)
                Index Cond: (y = '100'::double precision)
          ->  Bitmap Index Scan on test_x_2_y  (cost=0.00..4.30 rows=1 
width=0)
                Index Cond: (y = '100'::double precision)
(7 rows)

While I'm thinking how to combine it now.

BTW, while I was figuring out how create_index_paths works and creating 
bitmapscan indexes, I think I found a bug with unallocated memory (fix 
patch is bugfix.diff.txt). Without a fix here, it falls into the crust 
at the stage of assigning a value to any of the variables, specifically, 
skip_lower_stop and skip_nonnative_saop. I discovered it when I forced 
to form a bitmapindex plan for ANY (any_to_or.diff.txt). I'm causing a 
problem with my OR->ANY conversion patch.

-- 
Regards,
Alena Rybakina
Postgres Professional