Re: WIP: BRIN multi-range indexes

On 3/27/21 7:09 PM, Alvaro Herrera wrote:
> On 2021-Mar-26, Tomas Vondra wrote:
>
>> Hi,
>>
>> I've pushed both the bloom and minmax-multi indexes today.
>
> One thing I've been wondering all along is how useful are these
> BRIN-backed bloom indexes compared to contrib-supplied bloom indexes.
> My guess is that the BRIN implementation has some advantage, or you
> would not have worked so much on it. But what is it?
>

The contrib/bloom indexes are a completely different type of index. They
are not BRIN but a completely separate AM. The bloom filters are per-row
(so the index is larger than BRIN) and it's useful when you have table
with many attributes, and need to test various combinations of them.

create table t (a int, b int, c int);

insert into t select 10 * random(), 10 * random(), 10 * random()
from generate_series(1,1000000) s(i);

analyze t;

create index bloom_idx on t using bloom (a,b,c)
with (length=80, col1=4, col2=4, col3=4);

create index brin_bloom_idx on t using
brin (a int4_bloom_ops, b int4_bloom_ops, c int4_bloom_ops);

test=# \di+
List of relations
Schema | Name | Table | Access Method | Size | Description
--------+----------------+-------+---------------+-------+-------------
public | bloom_idx | t | bloom | 15 MB |
public | brin_bloom_idx | t | brin | 88 kB |
(2 rows)

So it's a completely different kind of animal, perhaps closer to btree
than to BRIN. I'm sure there are cases where contrib/bloom works better
than brin/bloom, but also the other way around.

regards

--
Tomas Vondra
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